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How to calculate CRI and CCT values for a light emitting material ? I have the PL data at ambient temperature, PLQE values and CIE co-ordinates.
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Sir i found different formula for CCT
CCT : -437 n^3 + 361 n^2 - 6861 n + 5541.31
which one is correct?
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I've recently been interested in studying Perovskite LEDs. The structure i used was ITO/PEDOT:PSS/MAPbBr3/ZnO:PEI/Gold.
(i) I am getting very low current for V-I characteristics curve.Is it okay?
(i)The luminous power is given in W/cm .How to convert it in watt /m^2
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divide BY THE DEVICE WIDTH
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I am trying to simulate a Single Quantum Well green LED using Silvaco. I want to see the effect of adding an insulator to the sidewall of the structure. However, when I do that, the current in I-V characteristics increases by 1 order of magnitude and I can observe a band bending in the insulator and the semiconductor. How do I resolve this issue to obtain a reasonable band diagram after adding insulator?
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The band bending and change of current is due to the surface states and surface recombination. Try to eliminate this by proper passivation
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Hello everyone,
I've been searching for 555nm(peak wavelength) high power LED for a long time. There are almost no types that can satisfy my needs. Well, the size should not be less than 3mm*3 mm because of the heat problem. Can anybody recommend any types?
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That's quite far away from 550nm...
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Dear Colleagues,
I need help in measuring the irradiance of blue light (455 nm) from LEDs in W/cm2 on petri dishes and surfaces using the following information.
Time f exposure to blue light is 60 minutes.
I determined that the used blue LED light was 455 nm.
The distance from the led arrays to the surface is 22 cm.
The surface area of the petri dish is 56.7 cm2.
Luxmeter measurement = 666 lux
Using a wattmeter, I confirmed that the wattage of the light is around 9 watts.
The box of the LED light has the following information:
Wattage = 9 W.
100 Lumen per watt
Lumen = 900l
Is there an equation or method that I can use to measure the irradiance ?
I appreciate your guidance and support..
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Dear Hassan,
let me try to help from a radiometric point of view.
First : please forget all photometric stuff such as lumens and lumen per watt for blue LEDs. The v(lambda) curve shows considerable variations in the blue and be sure that the wavelength of your blue LEDs does vary too for every piece.
So we stay with the radiant flux (= optical power) measured in Watt. Irradiance is radiant flux per area in W/m2. So I would suggest to take your wattmeter, put it at the same distance from the LEDs as the petri dishes, measure incident radiant flux and divide it by the area of the wattmeter's head area. That's irradiance.
Time is irrelevant for this considerations; if you multiply radiant flux by time you obtain the dose or radiant energy.
Hope this helps
Henning
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the following is a link containing the classification of the commercially available LEDs's semi-conductors and their approximate wavelength spectrum: https://www.researchgate.net/profile/Snehasish-Dutta-Gupta/publication/257761181/figure/tbl1/AS:392793823432709@1470660753744/Commercially-available-LEDs-with-colors-wavelength-range-and-material-used.png
the following is the link for some of the LED's wavelength emission spectrum classified by their semi-conductors: https://toshiba.semicon-storage.com/us/semiconductor/knowledge/e-learning/discrete/chap5/chap5-3.html
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Almost all commercially available LEDs (Especially in the range of the visible spectrum) are phosphor-converted LEDs, The table that you provided is for the spectrum of emitted light of the different semiconductor materials.
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I am calculating Responsivity of a pn junction photodiode by irradiating radiation from LED sources. For this purpose, i have two LEDs, one UV and another green LED.
For UV, manufacturer has given radiant power (~20mW). For Green LED, luminous intensity is given (in mcd). Viewing angle is 120°. Now, i have converted mcd into lumens by considering half of viewing angle as apex angle of a cone. Then, i did convert lumens into watts.
My question is, in literature, authors usually mention intensity in watts/cm^2. I got the values in watts, now how do i get to watts/cm^2? am i suppose to divide the power of LED in watts by the area of the photodiode exposed to radiation from LED? I have also seen some convert like this : "X mcd / m^2 into watts / cm^2.
Please explain how do i get from watts to watts/cm^2
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You've already figured out how to convert between radiometric and photometric units, which is often a point of confusion. That's a good start. So let's stick with radiometric units in specifying the characteristics of an LED. There are three quantities to consider (along with their photometric counterparts). First is radiant intensity R, measured in Watts / steradian (corresponding to photometric luminous intensity, lumen / sr). Then there's irradiance E, measured in Watts / m^2 (corresponding to illuminance in lm / m^2). And finally, there's radiance L, measured in Watts / m^2-steradian (corresponding to luminance in lm /m^2-steradian). LED manufacturers who are careful with their spec sheets, like Osram for example, usually spec their products carefully in terms of radiant intensity, e.g., 1.2 W/sr at 1A drive current measured on-axis over a small solid angle, e.g., 0.1sr. They also describe the divergence pattern that gives the half angle of the emission. You can convert from radiant intensity R to irradiance E at distance d (in meters) assuming that the emitter is a point source using E = R / d^2. That's a useful thing to use if you want to know the irradiance (W / m^2) on a target due to a given LED. Radiance can be used to discuss eye-safety since it measures the power per emitter area that ends up going into a given solid angle. Therefore, an LED with wide divergence and one with the same power per area at the emitter aperture but narrow divergence will have different radiance (narrow divergence -> higher radiance) and different effect on your eyes. Finally, you can integrate the total power over a sphere using the divergence pattern given by the manufacturer to understand the radiant intensity at a given angle into a given (reference) solid angle. Use polar coordinates to stay sane. That will ensure that the total radiant power (total optical power) is the sum of the power at each angle. Do this as a check. At that point, you will understand the emission of your LED and you can use E = R / d^2 to figure out what the irradiance (power per area) at any angle relative to the center axis will be. Hope this helps. See also, https://en.wikipedia.org/wiki/Category:Units_of_photometry and https://en.wikipedia.org/wiki/Radiometry for reference on units.
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In all the papers and books that I read, only the DC channel gain of the VLC system is studied without any further justification. How can we know for sure that the channel doesn't affect the frequency of the light? What would the spectrum of the channel look like with an LED modulated in OOK?
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The PD peak gain may be detected with just DC to measure the line loss as baseband frequency response is not usually the limiting factor except in extreme cases then using "eye patterns"
But the minimum signal for high speed is often >5% of peak to prevent reverse saturation. Thus there may be two Signal/Noise or SNR ratios for a 1,0 logic levels. The choice of levels for OOK depends on the SNR for each levels with noise and path loss and speed effects from Tx modulation methods and diode capacitance at 0V.
Jahid is overlooking that 630 nm to >1 um Red to IR is certainly the carrier like RF that has a loss factor [dB/km] and the photodiode, PD is the baseband detector to convert wavelength power to current.
If we can use "RG", then we can use OOK because those familiar will understand. But in all technical presentations, all abbrev.'s are defined first to avoid errors.
Generally, open loop DC gain and unity gain BW are both needed for baseband transimpedance amplifiers (TIA) to find the product of DC gain and unity gain fmax to get a gain-bandwidth (GBW) specification.
Unless it is a video broadband uncompensated amplifier, it will have an internal integrator cap that creates this GBW with very high gain and common Op Amp breakpoints are 10 Hz as a LPF..
Once does not really need DC gain for some bandband protocols such as bi-phase, FM, PSK, but OOK needs sufficient transitions to restore DC or actual DC coupling.
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I need white LED as an optical source in a Lumerical FDTD simulation. The LED light also needs to be of a certain CCT. Can anyone suggest me as to which sources to use and in what way? Thank you.
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Maybe this youtube video from Lumerical about OLED may help you.
OLEDs - FDTD - Lumerical Solutions - YouTube
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I am look to run experiments to test the effect of high energy visible light on biological or chemical samples (for example, illumination of biological ir chemical samples with Blue LED). Any tips or ideas for the setup would be great. Also suppliers of light and experimental setup.
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Here is the pptx....
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We were using the apparatus, the led was working fine and we were testing a rat. At one point the led shutdowns and then we couldn’t turn it back on....not even manually
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Looking at the item in question, I do not think it is advisable or perhaps even possible to dig into i enough to either diagnose or fix this problem. I think you have to send it back to Doric or buy another.
There are several things that could have gone wrong. First let’s consider things outside the light source. I assume you’ve checked to make sure your control voltage is still doing what you want. You hint that you have a multi channel source and only one channel isn’t working, so I’ll assume your applied power hasn’t failed. Similarly, I’m guessing the power-on led and any monitor screen show that the unit is alive. Perhaps your output fiber broke. Did you check for output light right at the output of the source? Several Doric models have current monitor outputs. Does the current monitor follow the control input correctly? If so, and there is no light at the output, most likely your LED failed in a shorted condition. If not, then probably your diode failed in an open condition, but several other electronic components also could have failed. You could have lost a supply voltage in the power control, but, again, other working channels says that’s not the problem. You could have blown an amplifier that follows the control voltage or more likely blown a transistor that regulates the led current. In any case, unless you are very handy with electronics (and don’t mind voiding any remaining warranty) I really think your only choice is to return it for repair or replace it.
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I need to use Rhodamine B dye in water for my project. The light source I am using is a blue LED. I wanted to know that if the excitation and emission wavelength of the Rhodamine B dye is same for all kinds of light like green laser light or blue LED light. If not, then what would be the excitation and emission wavelength of Rhodamine B dye in blue light?
Thanks in advance
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@Abbishek Gururaj, I am facing the same problem. Can you please tell me what happened afterwards.
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I'm starting to work with photodynamic therapy and photosensitizers (singlet oxygen generation etc.). Lights with a wavelength of 600-640 nm are suitable for the type of Phthalocyanine I have. Will any LED lamp at this wavelength that I can find anywhere (amazon etc.) work for me? Is there another important parameter I should consider?
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Dear Cansu Akyol thank you for sharing this very interesting technical question with the RG community. As a synthetic inorganic chemist I'm certainly not a proven expert in the field of photophysical studies. However, to the best of my knowledge you need an LED laser to study the photosensitizer properties of chloro aluminum phthalocyanine. You should also carefully study the relevant current literature about this topic to get an overview of what has already been done in this field. For example, please have a look at the following potentially useful articles which might help you in your analysis:
Evaluation of photodynamic treatment using aluminum phthalocyanine tetrasulfonate chloride as a photosensitizer: New approach
and
Photophysical studies of zinc phthalocyanine and chloroaluminum phthalocyanine incorporated into liposomes in the presence of additives
Fortunately these two articles have been posted by the authors as public full texts on RG. Thus you can freely download them as pdf files. Also please see:
Chloro-aluminium phthalocyanine loaded in ultradeformable liposomes for photobiology studies on human glioblastoma
This article is not yet accessible as public full text. However, all three authors have RG profiles. Thus you can easily contact one of them directly via RG and request the full text.
I hope this helps. Good luck with your work and best wishes, Frank Edelmann
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Is it possible to use filtered LED light to induce plasmon resonance, and thus heating of e.g. Au-NR, like using a pulsed or CW laser source?
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To answer your question: the photothermal temperature depends on the rate of energy input and the rate of energy loss to the surrounding. Although plasmonic nanoparticles have very high absorption cross sections, the heat generated is also lost immediately to the surrounding. Theoretically, an isolate Au or Ag nanoparticle in water requires quite high laser intensity at the resonance wavelength 1 mW/μm2 to achieve a local temperature of, let's say, 50 oC. This is like a million times the sun intensity. I did these calculations in two of my papers:
It has also been shown that a nanorod or a nanotriangle will have higher photothermal temperature than nanospheres due to higher absorption cross section. But this will still requite such a high intensity light source. The interesting aspect of plasmonic photothermal heating is the intense heating at nanoscale for targeted thermal therapy.
Now, whether you can achieve such a temperature with LED light depends on what is the mechanism you are putting in place to retain the heat. If you thermally isolate the nanoparticles (colloid or embedded in an insulating solid matrix), then a low power light source will also eventually heat up to a high temperature. This will not be any different from solar cookers for instance where a black surface can be used to capture heat and a glass box to reduce radiation losses. So it is possible, but the use of plasmonic nanoparticles for the heating needs to be justified.
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Hello,
For a project aiming to produce Spirulina production for human use, I am lokking for a pilot scale (around 10 or 20 thousand liter capacity) PBR supplier..
I will appriciate if you suggest a good company producing LED light integrated tubular PBR in Europe or Asia.
thanks alot for your help
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Thank you for all of yours suggestions, Schott proveide really high tech products but it is really expensive. BBI is no longer produce reactors in pilot or industrial scale. I didnt know algoliner, I will contact them. Thnaks again.
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Could you please clarify the theories related to energy and environmental pollution, I have to build arguments on the relationship between coal, oil, gas, and pollution.
1- Energy cost theory?
2- Energy LED theory?
3- EKC theory?
4- any other (please specify)?
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Other theories of energy and environmental pollution can "bridge" energy production and environmental and ecosystems conservation, like that of:
a) renewable energy sources (RES) for energy production, like cultivation of energy crops towards biofuels production. Here, the decision and social planning of land use (being a definite asset), they are prominent.
b) circular economy (CE), referring to energy savings from reusing degraded materials for a second round of use while alleviating/preventing natural resources depletion.
c) linking ecosystem service valuation (ESV) with circular economy valuation (CEV).
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Greeting for everybody
My question for estimating cooling load for any building consist of lighting
so how can calculate the cooling load for lighting ( LED lighting)
with my respect
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the amount of heat Qi produced by an individual lamp i is equal to the electrical power Pi *) picked up by this lamp times the operating time ('switch on' time) ti:
Qi = Pi * ti
This amount of heat is irrespective on the type of the lamp.
The total amount heat Q produced by all the lamps will be the sum over all Qi:
Q = sum(Qi)
Best regards
G.M.
*) the nominal electrical power (normally in W) is given in the data sheet of the lamp and is as well printed onto the lamp housing
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I turned on an LED and found the chip architecture was imaged onto the wall. this could lead a big trouble when I wanted to use this LED, but I couldn't know this via reading the spec. did anyone have the similar experience, how to resolve this problem ?
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Steven Ou LED design have many factors to be considered and these depend on various applications of the light, colour and temperature and few factors depending on the brightness and efficiency are also tdecided beforehe designing part.
This link shows some more details
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I have tried to use the conversion factor of 0.0079 which tends to work for sunlight but I'm aware that although the sad lamp is meant to mimick sunlight it isn't exactly the same, hence when trying to calculate power conversion efficiency ratings I'm getting ridiculous values. Any suggestions would be appreciated.
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Hi,
I am trying to get information on the UV module LED diode itself. If you have specs for the diode and a potential supplier, I would love to hear from you. Also, is there an instruction on how to change the diode without destroying the module?
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I'm wondering if you were able to find a replacement bulb and any instructions on how to replace it into the module?
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Many literatures use different sources of light.  I would like to ask whether 10W LED lamp or 300W xenon lamp is better.
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I think it depends on two things: the LED spectrum and the photocatalyst absorption spectrum. But in general, considering the power for photocatalytic applications, I guess it could be about two 10W LED lamps for one 300W xenon lamp.
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I' m considering building integrated LEDs on a standard CMOS technology.
What I do know: I can modify the bandgap energy if I use quantum dots in the range of 2..5nm.
What I need to learn:
How can I create an LED with such quantum dots. (Is it sufficient to simply create a PN junction that is only 2..5nm wide?)
Who can recommend literature how to calculate energy and momentum of the electrons is such quantum dots.
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Thanks for the overview Article of Quantum dot LEDs.
Looks like I have to add more precision to my question:
I don't want to use a III-V semiconductor and enhance it with quantum dots. I want to use Silicon itself and manipulate the bandgap by micro-structuring the silicon.
I have seen a publication of Frauenhofer Institute where the described using silicon pillars some nm wide to make silicon emit light. But unfortunately I don't have any further details.
Using avalanche Bremsstrahlung is an option I'm not really convinced of. Avalanching is destructive for the lattice and leads to fast aging of the components. I don't think a device based on avalaching will survive 10000h or more of operation.
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Light from an LED has a Lambertian radiation pattern, and the radiation pattern depends on the Lambertian order. And Lambert's mode number depends on the semi-angle of the LED. I have a clear understanding of the semi-angle of LED. But I am not able to understand the significance of Lambert's mode number and can't figure out that why we need this factor. Please anyone clarify.
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Kapila Wijaya Sri Palitharathna explains the function of the Lambert mode number m. Simply you need to draw curves for cos^m phi with m increases an integer say 1,2,3 and so on. You will see theta the radiation pattern becomes more concentrated near the angle phi =0.
Therefore m represents the directivity of the radiation of the light source in space.
Best wishes
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I think CuS is p-type direct band-gap semiconductor while LED is based on PN junction. So I hardly ever read papers in which CuS is used for light emission. If you have read correlative papers, please tell me.
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Unlike Enclosed fixtures that do not allow for proper ventilation can have a significant impact on the temperature of the LED bulb, causing it to overheat and shortening its lifespan. That's why some bulbs warn against using them in enclosed ceiling fans or fully enclosed porch light fixtures.
Best Regards
Dr. Fatemeh Khozaei
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In PhotoBioMedicine the units used are dose in J/m2 or irradiance in W/m2. But in the electrical it seems to be Illuminance and lux/m2 or lumen. I am wanting to measure the received dose from a Panel of 640nm and 850nm LED's. It will need to be measured at a precise distance, I understand, as it is divergent light.
Is there a simple light measuring tool to give me a reading in W/m2?
Is there a calculation to convert lumen/lux to W/m2 (at the specific wavelength)?
I am not looking for a calculation for lumen produced for a given watt of energy input.
Thanks for your help as I am getting out of my usual area.
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Dear Jayson,
Complicated but important question! All quantities related to the optical power using the unit [W = Watt], like the irradiance [W/m2] are radiative quantities and thus proportional to the number of emitted photons emitted by a surface or perceived by a surface. The area dose [J/m2] is the irradiance multiplied by the irradiation time. The integral power of a light/radiation source can be determined by an Ulbricht sphere and is expressed in W.
The illuminance is a photometric quantity and thus dependent on the spectral sensitivity function of the receiver, here the human eye. To this end, one need the eyes sensitivity curve, which is dependent on the illumination level. However, the illuminance [lux = lm/m2] is the visible light which illuminates a surface. For the calculation, you need the emission spectrum of the light source and the radiative flux. An example: A single LED with 1 W optical power and an emission spectrum with a luminous efficacy of 300 lm/W has a luminous flux of 300 lm, which is an integral quantity! If this LED illuminates an area of 1 m2 one obtains 300 lm/m2, which is 300 lux. (Remark: The angle dependent luminous intensity is expressed in Candela [Cd].
In other words, you cannot convert radiative quantities such as W/m2 or J/m2 without the knowledge of the emission spectrum into photometric quantities. More can be found in my lectures, which I add to this answer.
All the best for your research!
Thomas
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Good day everyone, I have a question concerning the DMIL LED Fluo / DFC7000 T Leica microscope. We want to perform an immunofluoresce assay by using this type of microscope with LED illumination for transmitted light. However we do not know what type of secondary antibody to acquire in order to perform the assay.
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Hi Karyna,
It depends which filters your microscope has equipped, what wavelengths they allow to pass through them and as Sebastian posted which wavelength your LED light is emitting at. Some LEDs are white light and will emit a broad spectrum for excitation (similar to a traditional mercury bulb). Others can emit specific colours. Most microscopes (including ours) blue (or UV) green (FITC) and red filters (TRITC) so DAPI, Alexa 488 and Alexa 594/633 are commonly used for imaging different primary antibodies. The Alexa antibodies (Thermofisher) are quite reliable, with low background (used at a dilution of 1:100-200) and Vectorshield mounting media can be bought with DAPI in it for nuclear localisation. That would give you suitable separation between antibodies if you are using multiple primary antibodies from say rabbit and mouse. If you are just using one primary antibody use the Alexa 488 which will work reliably on any green/FITC/GFP filter.
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In most of the studies of patients with osteogenesis Imperfecta (OI), application of bisphosphonates led to a beneficial increase in bone density (measured by DXA). What is your experience in this topic?
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In our research, we found that Bisphosphonates increased oral bone volume in osteogenesis imperfecta. These findings corroborate with the findings in the medical field about the increase in bone volume with bisphosphonate treatment.
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frequency response of an LED
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Excellent considerations
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I am currently using a simple 8mm focal length lens from Carlco to focus my light from a single small LED into a bundle of fibers that have a total diameter of 9mm. The problem I am having is that I have a high intensity of light at the center of the bundles and the light falls of by at least a factor of 2 at the edge of the bundle.
I make a commercial product and need a lens that is not more than USD10 in cost if possible.
Can any one point me in a good direction please?
Thanks, Michael Groves
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A homogeneous coupling of light arising from an LED into a fiber (or fiber bundle) is best achieved by two lenses. First an aspherical lens with a focal length of e.g. 10-20 mm and an NA of 0.6-0.8, second a lens with a focal length that is somewhat longer to re-project an image of the LED die into the fiber entry. In your example (9 mm fiber bundle), a 1x1 mm² LED die would be best collimated with a 17.5 mm aspherical and re-projected with a f=160-200 mm lens. In the infinity space between both lenses, dichroic mirrors may be inserted to combine various LED colors for fiber coupling.
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Is there any photosensitizer that can generate different types of ROS upon different light irradiation? I understand my question is kinda confusing so I added an example below this.
(E.g., When the photosensitizer is irradiated by white LED light, it generates singlet oxygen mostly. On the other hand, when it is irradiated by green LED light, it generates radicals mostly.)
I want to find something about detection of ROS content produced by different light irradiation to the photosensitizer.
If you guys can find any journals that can answer my question, pls let me know! thank you.
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Photosensitizer based Journal about conversation and storage
International Journal of energy research, International Journal of Electrical power and energy system, energy source A,etc.
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Are there linearly polarized LEDs already available on the market?
If you wonder, normal led emits non-polarized light, or has different elliptic polarization depending on the direction. But almost 10 years ago people started researching configurations, emitting light with uniformly arranged linear polarization in main direction. Some circularly polarized LEDs were reported.
But I still can not find any manufacturer offering linearly polarized LED for money.
Please do not be confused by "(un)polarized LEDs" trade name. Unpolarized LEDsare just dual-LED assembly allowing flipping "+" and "-", which are also compatible with AC; "polarized" stands for normal diode.
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I'm also looking for the polarized LED, actually polarized micro-LED for display applications. If you found any solution, please let me know.
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How much power (in watt, equivalent to one joule per second) we need to improve fluorescence emission of indocyanine green (ICG) using a 780nm LED? Is there a minimum power for that?
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No, there isn´t. You just have to take in account the small stokes-shift and quantum efficiancy. You need good steep filter sets and good sensitivity on detection channel.
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I am growing Solstice wheat under LED grow-lights and the leaf tips are drying out and going brown. The watering is the same as before they were moved to this grow-room, which makes me think it's an issue with the lighting - is this a problem others have encountered before?
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Hello all,
I have some idea on how to measure the external quantum efficiency for my perovskite LEDs, but I want to calibrate that setup for which I want to measure the External Quantum effficiency of a normal 5 mm LED. How should I go forward with it? All suggestions/ help would be appreciated. Thank you
Jitesh Pandya
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Adding to the colleagues above, you can use a standard solar cell in the shortcircuit mode pf operation where the out put photon flux of the diode can be recieved by the solar cell provided that the area of the solar cell is made large enough to receive the whole flux of the LED.
If the spectral response S(lambda) in mA/ photonic power of the solar cell is measured at the wavelength of the diode then one can get the the input photon flux what is that emitted from the diode at the same time, one can calculate the
input photonic power as Pphotonic= I/ S where I is the measured current and and S is the sensitivity at the intended wavelength.
If elaborated this method can work well in spite of its simplest.
Best wishes
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Greetings everyone , I've managed to control LED light with simple brain waves ( emotive epoc x ) . But I need to control the value for example ; the value range is from 0 to 1 so when the brain reading of a simple task goes above 0 the LED light turns on but sometimes even when its 0.00 the light turns on , any idea how do we control this range .
I will upload the code ...
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Abdulrahman Alsulaimani I'm hoping for the best! Let me know if it works, anxious for news!!
Don't need to apologize. I hope to hear from you soon, Roberto Ceccato
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The switches are to switch the leds on in an order.... When order of switcjes is altered the leds don't switch on
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Statemachine...
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In the structure of light-emitting diode construction, people talk about the active region in between p and n-type semiconductors. Why do we require that active region? Is that active region just the depletion layer of pn junction diode? If so why do we need an active layer in LED?
Can someone help me in understanding this concept?
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In principle, the active region of LED could consist of depletion region between n- and p-type layers of the same material. For examples, the first blue LEDs were of this type (GaN codoped with Zn and Si). However, modern LEDs use some type of heterostructure (quantum wells or quantum dots) as an active region sandwiched between n- and p-type material. For example, blue LEDs consist of nGaN, InGaN/GaN quantum wells/barriers (= active region), and pGaN (+ some other layers like AlGaN electron blocking layer etc.). The advantage of this concept is mainly:
1. InGaN alloy has smaller bandgap than GaN. Therefore, the light emitted from InGaN QWs has lower energy than GaN bandgap and is only weakly reabsorbed in the GaN material.
2. InGaN QWs form potential minima for electrons and holes. Therefore, excited carriers tend to accumulate in QWs. High concentration of carriers means high probability of radiative recombination. The non-radiative recombination through deep non-radiative centers is relatively suppressed in comparison to bulk material as the concentration of non-radiative centers inside QWs is limited but the concentration of accumulated carriers is high. On the other hand, high concentration of carriers can lead to non-radiative Auger recombination.
3. In the case of InGaN/GaN heterostructure, the InGaN alloy is very beneficial to suppress the non-radiative recombination through dislocations which are usually present in high concentrations.
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I would like to do an experiment that uses white LED lights set in different intensities for each group of plants.
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Not a simple answer. As always you need to learn more about stuff you are using to achieve your goal.
Actually it wrong terminology. Probably you need to provide different illumination delivered to the plants.
(A) you can use the same LED intensity (Power) setting but need to change the distance from plant. Need to use illumination meter to record illumination.
(B) you can use the same distance bu change LED Intensity (power - driving current). Also you need illumination meter to calibrate set-up.
Good luck,
Branko
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Hello,
As a part of my research project, I am trying to create a 1mm(w)*3mm(l) rectangular (beam) of collimated light. I am using LED as a light source because I need a wavelength range of 300nm to 1100nm for my spectral calculations. I tried to collimate the light with the help of a parabolic mirror.
I could collimate the light for 10mm dia circular slits. The beam divergence is very small around these diameters. But when I try to pass the light through a 3mm*3mm vertical slit I can see that the beam divergence is very larger compared to the previous circular slit. A 9mm*9mm rectangular projection appeared on a projector which is around 100 cm away from the vertical slit.
There was a funny phenomenon when I tried to use a 1mm*3mm vertical slit. There were 2 bright lines on the projector screen with a gap between them. I used the same setup which I used for circular slits but I couldn't understand the reason behind this behaviour.
Ideally, I need 1mm*3mm rectangular collimated light with this setup (for over a distance of 100cm). But I would be happy if I can achieve at least a 3mm*9mm collimated light (beam).
I have attached the photos of the Light setup with a parabolic mirror. I would kindly request any information or solution that can help me to resolve this issue.
Many thanks in advance.
I would be happy to provide any further information.
Best regards,
Vayalthota Gopikishore
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(1) Any collimated light has a divergence that depends of light source size and collimator focal length. In this case there is no clear data about collimator divergence. For that you want to achieve your collimator should have divergence less than 6 mRads.
(2) When narrow slit is illuminated with collimated beam you can have diffraction effects that contribute to additional beam changes.
(A) You need to learn more about collimation and rearrange your set-up to get proper collimation.
(B) you need to study in more details diffraction effects to understand what is happening.
(C) you need to reconsider the purpose of your experiment and analyze how mentioned effects affect your purpose.
Good luck
Branko
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Hello all
I am currently working on lead halide perovskites that are bromine-based. The issue with my material is that it falls out of phase very quickly under ambient settings, and I am trying on ways to keep it more stable, such that its PL also does not degrade. Any suggestions on how I can solve this problem?
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Dear Jitesh Pandya many thanks for your very interesting technical question. te synthesis and processing of lead-perovskites is an important current research topic worldwide. Thus there is a large body of scientific literature available worldwide. From the outside it is difficult to solve your specific problem without knowing the detailed reaction conditions (target compound, starting materials, solvent etc.). For an alternative synthesis of methylammonium lead bromide perovskite nanocrystals using ionic liquids please have a look at the following relevant article:
A facile, environmentally friendly synthesis of strong photo-emissive methylammonium lead bromide perovskite nanocrystals enabled by ionic liquids
Unfortunately this paper has not been posted as public full text on RG. However, the Supplementary Information is freely available (see attached pdf file).
Also please have a look at this potentially useful paper:
Blue-luminescent organic lead bromide perovskites: highly dispersible and photostable materials
There are also a number of interesting references describing the crystallization of lead bromide perovskite materials. For example, please go thorough the following Open Access articles:
Synthesis of centimeter-size free-standing perovskite nanosheets from single-crystal lead bromide for optoelectronic devices
and
Optical Characterization of Cesium Lead Bromide Perovskites
Moreover, I strongly suggest that you use the "Search" function of RG to find and access relevant articles in this field. As an example, you could search e.g. for the term "lead bromide perovskite" and then click on "Publications":
This will provide you with a long list of useful articles.
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Hi, I am wondering if anyone has used Light emitting diode (LED) as a photon detector for measuring fluorescence life time ? Previously I used to use either a fast photodiode or a gated CCD camera for such a measurement, but i don't have these detectors anymore and i am searching for a cheaper alternative. I will appreciate any suggestion. Thanks!!!
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The intrinsic risetime 10/90% of 25MHz oscilloscope should be order of 14nsec (the proportional rule is 50MHz --> 7nsec).
However, the coax cable capacitance is 100pF/meter, typical LED may have zero-bias capacitance of tens of pF plus few tens ohms of series resistance. Zero-bias is not good way for high speed operation, one needs strong reverse bias.
You may also have a look at vaccum phototubes like (if you want large area at high speed) https://www.ebay.co.uk/itm/124522822494?hash=item1cfe237b5e:g:4UoAAOSwcbhf~CnX
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I have some red, blue and white LED bulbs (5 watt) I want to know the actual light intensity values (lumens/PPFD) and wavelengths of red blue and white light spectrums. Is that possible?
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Dear Udara,
The spectral power distribution can be determined by a typical fluorescence spectrometer, e.g. from Edinburgh Instruments or Ocean Optics. In order to determine absolute values you need a calibrated Ulbricht (integrating) sphere as pointed out beforehand. However, you have to keep in mind, that the spectra of LEDs shift and quench with temperature and drive (power density). Thus the results will depend on the adjusted measurements conditions.
All the best for your research,
Thomas
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Greetings,
I have noticed that some of chickpea leaflets started to develop a whitish color on the edges while the top portion of the leaflet is still green, could this be due to some sort of a deficiency?
The experience was conducted in pots (containing a mixture of soil, sand and compost) which were kept indoor under LED light (70% red, 30% blue), pictures are linked below.
Thank you.
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It can be photobleaching. Prolonged exposure to excess light causes photoinhibition, that is decrease in photosynthetic activity, followed by chlorosis – bleaching of chlorophylls. (see )
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Please any one can suggest me, that how to calculate the EQE of an OLED from the available data of Luminance (cd/m2) and I-V or J-V curve data of an LED with out using an integrating sphere? I went through few previous conversation, but not clear for me. It will be quite helpful, if any one can help me in this regards.......
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Guo, Haoqing, Qiming Peng, Xian-Kai Chen, Qinying Gu, Shengzhi Dong, Emrys W. Evans, Alexander J. Gillett et al. "High stability and luminescence efficiency in donor–acceptor neutral radicals not following the Aufbau principle." Nature materials 18, no. 9 (2019): 977-984.
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I would like to know is working in the field using LED light traps to monitor and to reduce populations of Lepidoptera pests in forest plantations.
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Hello José:
I use Led black light to monitor Coleoptera (Melolonthidae) and Lepidoptera with great success. The advantage of led light is that it consumes much less energy and the 12 volt battery lasts longer (8 hours) one night. The largest catch in one night were 10,000 individuals of Phyllophaga, Cyclocephala, Anomla and Plectris among other orders and families.
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Hello all,
I am working on perovskite LEDs currently, . I observe that testing the LED at a voltage sweep from 1-5 V, the perovskite LED s glow once, but they eventually die down. Also I cannot maintain a constant voltage on the LED. What could be the reason? I am using SnO2 ETL and TFB HTL. I wanted to know how to make sure that I can maintain a constant voltage and also ensure that the LED is operationally stable?
Any help is appreciated
Thanks
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There are two main reasons for such behavior of your device!
- The first cause may be due to damaging your device by too high constant voltage source!.
In order to test diodes it is required to test the diode with constant current source
rather than consatnt voltage source.
If you use a voltage source then you have to limit the current in the diode by a proper series resistance with the diode!
- The other less probable cause is device instability because of the moisture and oxygen effect on the perovskite material.
This can be overcome by a test environment free of moisture and oxygen.
Please if you made investigations please report to us!
Best wishes
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Hi,
I am trying to measure the change of the refractive index (RI) of my sample by measuring the OPD with a QWLS wavefront senor. For this aim I have two different setups. My first setup is the combination of a routine upright microscope and my wavefront sensor, and the second setup is a simple combination of a light source (LED), a collimator, and the sensor.
The results obtained show that the measured value for Δn in these two setups are different. The comparison of the obtained values with the theoretical values confirms the values obtained with the second setup, but not the values obtained with the first one. Furthermore, I have obtained different OPD values for the measurement with different magnification, which I cannot understand.
I would be thankful if anyone could explain me, what is exactly happening in the measurement with the microscope, and how the different microscope parameters like magnification, NA,... affect the OPD.
Best regards,
Fatemeh
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Anouar Jbeli Thank you very much for your guidance.
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Hello,
I am a device-level engineer and am looking for a time-of-flight measurement kit that contains time-to-digital converters (TDCs) so that I just connect my fabricated PD & LED to this kti and perform the depth ranging capability.
I found one product like this:
but, it's now obsolete and not available. Purchasing only the TDC component does not fully resolve this issue because additional external passive electric parts, packaging, and hardware-level programming schemes are required. Is there any product for this project? Thank you!
Best,
Ted
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Dear Aparna,
Sorry for the late notice of your post. The product you posted already contains packaged laser & photodiode. I may need to substitute them with my fabricated LED & PD, which is the tricky part. Thank you for the suggestion though!
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As the title says,only the LED turn on voltage of cspbbr3 is 4v,but the hybrid pbcl startup voltage becomes smaller between 2-3v。
Theoretically, the cspbbcl band gap is relatively large, so the turn on voltage should be larger.
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The mixed two semiconductors form intermediate energy levels, comparing with the pure material emitter, thereby lowering the charge carrier injection barriers. It leads to decrease the turn on voltage.
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rare earth ( Yttrium / europium and gallium) are known as embedded in larde TV screen. ( or jumbotron devices).
to compute the global impact, I need good sources providing the individual content of 1 LED , the number of LED, and the estimated amount of screens sold.
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Dear Thierry Hanau thank you for your interesting technical question. For a general overview on the various technical application of rare-earth elements please have a look at the following review article entitled
Rare earth elements: A review of applications, occurrence, exploration, analysis, recycling, and environmental impact
Also please see this relevant review article:
Taking Advantage of Lanthanide Luminescent Ions
Both papers are freely available as public full texts on ResearchGate.
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I need a tesla coil at least like 3 or 4 times larger than what I currently have (a 15V/2A output) it WORKS but my LED must be like within an inch of the keychain sized tesla coil! …all the kits are to build SMALL SAME SIZE OUTPUTS OR ARE WAY TO BIG (and dangerous, not to mention expensive as hell too!!!)!!!
Please if anyone has some guidance or hep on how to know like if i make 1 from scratch how do i know how may turns of Wire do I need in my coil and things like resistor sizes and ALL of that if it is not in a ore assembled "kit" but again, they do not build what I need, or build WAY TO COMPLICATED and dangerous stuff to even attempt to be honest...)
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I advise you not to trust the advertising promises of the kit manufacturers. A long procedure of tuning the transmitter and receiver into resonance awaits you. No guarantee of successful completion. If you have problems reinstalling the mains plug, then I do not advise you to engage in any experiments with the Tesla coil.
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Hi All,
I have placed an order to purchase tissue culture rack with fluorescent bulb (Tube light), but the company recommends that they will offer me a LED unit with the same price.
So I would like to know anyone uses the tissue culture rack with the LED lighting systems? then please share your experiences?
Advantages and disadvantages of LED tissue culture racks as well.
Thanks in advance.
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LEDs are more preferable as they have long lifespan, low energy consumption and they provide specific wavelength of light. Again, due to lower thermal emission, the LEDs can be placed much closer to the plant and this close proximity can provide greater concentration of photons leading to better photosynthetic productivity. Moreover, the disposal of LEDs is more environmental friendly than the mercury containing Fluorescent bulb.
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I would like to make photoluminescence measurements of GaN material at room temperature. At the moment I do not have a laser that I could use for this purpose. Can I replace the laser with an LED?
What are the disadvantages of such a solution?
Thank you very much for your help!
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I will not repeat what has been said by the colleagues.
You can use LED array and collimate their light by a lens.
This will give you nearly monochromatic light with high intensity.
You can use also power LEDS. It can also excite the electrons from the valence band to conduction band according to its yellow and blue mixed light.
I would advise you to try them you will not loose nothing, you will gain.
Best wishes
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Regarding patent: PCT/IB2020/053346
I have found several kinds of millimetric-size UV-C lamps having a price of $2-$4 (retail) that makes
the implementation of this kind of respirator commercial and enough small. output power is several watts. on the other hand laser and LED UV C emission doesn't produce emission.
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very good question
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I want to illuminate a scene (small space) using LED to capture photographs or videos of some tiny objects inside the space. But am not sure if I should use a Laser LED, or simple LED or power LED. The volume (space) that needs illumination is about 125 cm^3. The walls will be painted white in matt finish to maximise illumination under minimised shining effect. Instead of of using a camera I may want to detect an object as an obstacle in front of the beam of light emitted by the diode. Which diode shall suite the most ?
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Dear @ NandKishor,
welcome!
Laser are concentrated light beams with high coherency. It is not used to illuminate areas. To illuminate areas and volumes you use power LEDS they are intended for such applications. For photography and video may be the best type of light sources for small volumes is to use white power LEDS.
Best wishes
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I'm wondering if anyone can helps to download this tool, we aim to use this tool to explain to students how the led device works, also to realise some examples in 1D and 2D.
Thank you very much in advance & Regards
Hichem
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you can send an email to the support of this software
The license is not available in a single file or can be sent online
instead, it is a dongle based
so, you have to send a request to them and wait for them to send you the dongle USB
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Recently MCI now NMC has made it mandatory to use only Non mercury Sphygmomanometer for teaching practicals to MBBS students. So I want ask which is technically better option, Android or Non-Mercurial LED Sphygmomanometer for teaching?? Please share experiences from those who have already used either of them.
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Mercrial sphygmomanometer is a good choice for students training
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I need to know how to control LED based on a camera barcode scanner.
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What is the tools you have to accomplish this target ?
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I have seen many papers where the authors synthesize luminescent materials, and then coat those materials on top of UV LED chips and publishing them as phosphor LEDs. I want to make such a device. Can anyone tell me where I can purchase these UV LED chips in India?
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Hey all,
I need to make an LED light (5x5mm) that can produce an 80mm diameter beam from about 450cm away using a 20mm lens.
From what i've read, I can use a plano-convex lens to collimate light from a light source. If I use a 20mm lens, a perfect light point at the lens's focal length would produce a 20mm diameter beam correct? However, since it's not a point, the light would slightly diverge. I wanted to use that to my advantage to create a beam as mentioned above.
I read you can use the focal length as well as placing the LED in away from the focal length in order to produce a larger beam diameter at a certain distance away, but I couldn't figure out the calculations. I was wondering if anyone can help me figure this out.
Thanks so much!
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The glass is indeed an optical planar window glass (bk7 glass) and its refractive index is also 1.5.
The incoming light has an angle, says 30 degree respect to surface of this glass.
We would think the moved positions from the mirror going out of the surface of the glass and also the both scattered and reflected light reaching to surface of the glass might be cancelled out.
Having said that as much as light from the glass to mirror is moved to the left hand side, the scattered/reflected light from the mirror to the surface of the glass will be moved to the right hand side.
Therefore we will get neglectable moved position in total when the light is coming to the second lens and then to the photodiode.
I would be happy to hear your points regarding this matter.
I am managing this project and would be happy to discuss further the rest of the details with you via skype or email.
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77
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Tachometer can be used for speed detection.
Instead of Led, we can use sensors and actuators for bicycle.
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Hello, I am a recent graduate and I recently joined a company that makes street lighting lamps. All good and beautiful until I was told that I had to look for a driver for LEDs that would convert a direct current of 12 to 24 volts into a direct current of 36 volts. The main question is what device do I need to control the power? For example, the LEDs would draw 36 volts, how I can change the output current so that they can adjust the power they consume, for example 50w or 30w. The power supply would be made by two 12v batteries connected in series, which output 4 amps at 24v. Any links would be helpful, thanks!
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Firstly, terminology: Current is measure in Amps, not Volts and we use caps because those units are named after people - Ampere and Voltaire. Also W for Watts. Pardon my pedantry ...
Secondly, search the internet for a "DC to DC converter". Try to find one with a smooth output - cheap converters can have a chopped output waveform which is not really "DC".
There's some converters here:
Good luck ...
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How far Infrared sources are eye safe while working with Vehicular Communication? I read two research papers by Isumu Takai etal. where Infrared LED array consisting of 100 LEDs is used as the Light source(870 nm LEDs) .how far is this practice eye safe ? even if u consider 1550nm LED's they are hardly available in India. Whether we should consider IR LEDs or Visible LEDs for vehicular communication? Incase if we use IR LEDs are there any precautionary measures to be taken to avoid damage to eye ? Please Let me know
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This sounds like the perfect question for an animal model study. Also, some work at Mitsubishi on MIR emission from arc lamps.
As an ignoramus, I would not want to be too close to a power LED at 870 nm. In a car application, severla feet = probably OK (?); security app, ditto.
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Hello,
I'm a university student who is currently doing a plant incubator project, which requires LED grow light system. One of the project objectives is to provide a wavelength-tunable light source, so I plan to combine 4 LEDs (with different wavelengths) into a single source. One of the example I saw from papers is they design a freeform TIR lens for color uniformity via commercial software. But I was wondering if there is any other way to combine and collimate the LED beam via lens/optics?
Thank you.
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Dear all,
I agree on Henning! In other words for horticulture lighting you do not need to regard the CRI, but a good overlap with action curves (photosynthesis rate, chlorophyll formation and so on) of the specific plant. You can find some relevant action curves in the DIN regulation 5031-10.
All the best,
Thomas
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We have 10 glass boxes with 6 inches width and 12 inches depth. How many LED bulbs or halogen lamps will be required to achieve irradiance of 150 umol/s/m2.
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I am using the light source as LED spotlight 50W (MFG part no: MASTER LED ExpertColor LED MR16 ExpertColor 7.2-50W 927 10D ). Hence i am planning for lens mechanism to convert the divergence rays to collimated one. The beam divergence angle of the light chosen is about 10 degrees. It would be nice if someone suggest the lens mechanism for collimation. I thought of using Plano- convex lens. Kindly suggest me which one to prefer.
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You can use camera objective lenses with variable f ratio or simply by using a conical lens
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Hello all
Thanks for answering my previous questions. I am making perovskite LED and intend to use PEIE on zinc oxide layer as ETL. But I am not sure what version of PEIE to us. There is the one with Mw 70000 g/mol which is not available , but the one with Mw = 110000 is available. But I am reluctant as I do not what effect high molecular weight will have on the performance of LED. I anyone could guide me with this it would be helpful.
Thanks
Jitesh
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The ETL must satisfy specific requirement to function properly:
- The electron concentration must be as high as possible.
- The mobility of electrons must be also as high as possible.
- The energy levels must must match those of perovskite.
The lumolevel of the ETL must be lower than the conduction band of the active layer.
What is the effect of the molecular weight on these parameters must be known to judge which material alternative will be more suitable.
I would propose that you pragmatic on the issue and make planned experiments with the materials to evaluate it. Or you can measure the electronic properties of the material to assess its properness.
Best wishes
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I have fabricated ZnO based p-n homojunction diode with turn-ON around 4V current at 80mA. PL spectra shows strong emission in UV region (375 nm). But I am unable to view any UV/visible emission during electroluminescence study? What could be be the probable reasons? The device structure is as follows:
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Sure I came very late to this question. Hope you succeeded to get electroluminescence from you structure.
It is normal to get photoluminescence from the any homogeneous semicondcutor.
In order to get electroluminescence you must have a diode structure.
The easiest method is to measure the I-V characteristics both in the forward and and in reverse direction. The type of conduction can be easily determined by the hot probe method.
For more information please follow the link:
Best wishes
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For some research purposes, there is a need to acquire high-quality YAG phosphor powder with known optical properties and particle diameters. I would be pleased if you can share your knowledge on providers or manufacturers which we can buy powder in small quantities.
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Hi Azarifar,
You may make an inquiry at Alfa Chemistry, they offer kinds of good-quality chemicals.
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Conventional light sources have a penetration depth of a few nanometers in metal layers and cannot be used for spectroscopic ellipsometry purpose to measure layer thicknesses of a few 100 nanometres.
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Hello Ernst,
I think there is no chance to measure metal layer thickness of a few 100 nm by ellipsometry in the spectral range where conventionnal instruments operate today that is from VUV to IR, whatever the source.
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Thanks a lot for your answers.
I have one more question: after synthesizing ZnO nanoparticles , I am not able to separate from the original solution (dispersion actually). The recipe is as follows:
1.5 mmol Zinc acetate dihydrate in 15 ml DMSO stirred at 30 degree celsius. then 2.8 mmol tetraethylammonium hydroxide pentahydrate (TMAH.5H20) in 5 ml ethanol is dropped in the solution. The solution is kept stirring 24h prior to the precipitation process. The ZnO nanoparticles were precipitated by ethyl acetate, and washed with ethyl acetate and ethanol for one more time. Finally, the obtained ZnO nanoparticles were dispersed in 8mL ethanol and filtered with 0.45 micron filter before use.
I have some major questions in this process:
1. How can I separate the ZnO NPs for washing? I tried centrifugation at 6000 rpm but i could not get rid of the solvents (DMSO and ethanol).
2. What is the volume of ethyl acetate to be dropped for the precipitates?
Please it would be great if anyone could help me resolve this issue.