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Specific blue-red spectrum LED light sources have generally been used for horticultural lighting applications within interior environments. However, this small-scale qualitative pilot study comparing two plant-growth profiles reports that white LED light sources normally used for architectural lighting applications are biologically and visually more effective for horticultural lighting applications within interior environments. First profile involved three vegetable species namely, lettuce, parsley and tomato under three LED light spectrums-specific blue-red spectrum (460+630+660nm), full-range blue-red-white spectrum (380-730nm), and white full-spectrum (400-750nm). Second profile involved a collection of ornamental plant species under two colour temperatures of white LED light-warm-white (3000-kelvin) and neutral-white (4000-kelvin). Overall observations suggest that spectral properties of white LEDs, which mimic certain qualities of natural sunlight, have more advantages over blue-red LEDs such as stimulating plant metabolism for improved growth and better health, while rendering a natural appearance to plants. These observations may encourage the use of white LED light sources for both architectural and horticultural lighting applications within interior environments.
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International Journal of Horticultural & Crop Science Research.
ISSN 2249-4243 Volume 9, Number 2 (2019), pp. 83-93
© Research India Publications
http://www.ripublication.com
White LED Light Sources Merging Architectural
and Horticultural Lighting Applications within
Interior Environments
1Amardeep M. Dugar, PhD
Lighting Research & Design
Flat#3 Bhavana Apartment
F-142 8th Cross Street, Anna Nagar (East)
Chennai 600 102 TN India.
2Manju Dileep
Ruud Lighting Arabia
Dubai, UAE.
3Hussain Burhani
Hazel Lighting
Mumbai, India.
Abstract
Specific blue-red spectrum LED light sources have generally been used for
horticultural lighting applications within interior environments. However, this
small-scale qualitative pilot study comparing two plant-growth profiles reports
that white LED light sources normally used for architectural lighting
applications are biologically and visually more effective for horticultural
lighting applications within interior environments. First profile involved three
vegetable species namely, lettuce, parsley and tomato under three LED light
spectrums specific blue-red spectrum (460+630+660nm), full-range blue-
red-white spectrum (380-730nm), and white full-spectrum (400-750nm).
Second profile involved a collection of ornamental plant species under two
colour temperatures of white LED light warm-white (3000-kelvin) and
neutral-white (4000-kelvin). Overall observations suggest that spectral
properties of white LEDs, which mimic certain qualities of natural sunlight,
have more advantages over blue-red LEDs such as stimulating plant
metabolism for improved growth and better health, while rendering a natural
appearance to plants. These observations may encourage the use of white LED
light sources for both architectural and horticultural lighting applications
within interior environments.
Keywords: LEDs; white light; full-spectrum; architectural lighting;
horticultural lighting
84 Amardeep M. Dugar, Manju Dileep, Hussain Burhani
1.0 INTRODUCTION
The practice of horticulture1 enabling cultivation of plants for food (fruits,
vegetables) and ornamental use (cut flowers, potted plants, shrubs, trees and green
walls) within interior environments has been prevalent for several years. Of the
many resources required for growing plants within interior environments, light is one
of the most important2 apart from photosynthesis, it is required for several
physiological processes in overall plant development such as photomorphogenesis
and reproductive stage development3. While natural sunlight has the perfect balance
of fluence and wavelengths necessary for plant growth4; greater control over the
growth and development of plants is possible by the appropriate use of artificial light2.
Research5 from the Illumination for Plant Health Alliance at the Lighting Research
Centre at Rensselaer Polytechnic Institute has shown that precise doses of artificial
light can be used to combat the many pests and pathogens that reduce crop yields as
well as increase plant health.
Agronomically, light-emitting diode (LED) technologies have the potential to cover
fluence and wavelength requirements of plants, while allowing specific wavelengths
to be enriched, thus supplying the light quantity and quality essential for different
phases of plant growth4,6,7. The idea that plant growth under natural sunlight could be
mimicked using blue and red LEDs has generally led to blue-red combinations being
used in artificial growing systems4: red (650-665nm) wavelengths perfectly fit with
the absorption peak of chlorophylls and phytochromes6,8; supplemented blue (460-
475nm) wavelengths allow higher photosynthetic activity by providing better
excitation of different types of photoreceptors6,9. However, research confirms that
specific blue-red spectrum LEDs used for functionalistic food production cannot be
applied for the lighting of ornamental plants: the spectrum enables fast growth for
market consumption usually making plants appear unnatural; whereas illumination of
ornamental plants in an interior environment should help them grow at an appropriate
speed, which reduces maintenance costs, and provide them with a natural
appearance10. Additionally, plants appear purplish grey under blue-red spectrum,
which makes visual assessment of plant health difficult11.
This small-scale qualitative pilot study argues that white LEDs normally used for
architectural lighting applications offering all the main bands of wavelengths in the
photosynthetically active radiation (PAR) spectrum (390-700nm) enable plant-growth
at an appropriate biological speed, while rendering a natural visual appearance to
plants within interior environments. The study explores the advantages of full-
spectrum (400-750nm) white LEDs over conventional blue-red combination LEDs in
terms of energy and information for plant-growth, thereby ensuring better
manipulation of plant metabolism. Additionally, as specific blue-red spectrum LEDs
makes plants appear unnatural, the study explores how white LEDs render plants their
natural visual appearance thereby making them more conducive to the people living in
these environments.
White LED Light Sources Merging Architectural and Horticultural Lighting 85
2.0 MATERIALS AND METHODS
Two different potted plant-growth profiles were established for two different types of
qualitative assessments. The first profile was designed to assess which of the
following three different LED spectral combinations is biologically more effective for
horticultural lighting applications: specific blue-red spectrum (460+630+660nm), full-
range of blue-red-white spectrum (380-730nm), and neutral-white (4000-kelvin) full-
spectrum (400-750nm). The second profile was designed to assess which of the
following two different colour temperatures of white LED light normally used for
architectural lighting applications is visually more effective for rendering a natural
appearance to the plants: warm-white (3000-kelvin) and neutral-white (4000-kelvin).
2.1 Materials and Methods Profile-1
A service room within a residential apartment in the city of Dubai, UAE that did not
have any penetration of natural sunlight was selected for this plant-growth profile.
Three different vegetable species were selected namely, lettuce, parsley and tomato
based on their differing requirements of photoperiodism or light hours for flowering
as depicted in Table-1. Each of these types of plants were sown in pots and placed in
identical canopy boxes of dimensions (60x60x60cm) as shown in Table-2: Case-A
was illuminated using a 12W Essential Choice grow-light source comprising clusters
of 12 LED sources (3x Red 660nm, 6x Red 630nm, 3x Blue 460nm) providing
specific blue-red spectrums (460+630+660nm); Case-B was illuminated using a 28W
Esbay Bulbs grow-light source comprising clusters of 28 LED sources (15x Red, 7x
Blue, 1x IR, 1x UV, 2x daylight-white 5600K, 2x warm-white 3000K) providing a
full-range of blue-red-white spectrums (380-730nm); Case-C was illuminated using a
20W CREE light source comprising a single LED chip providing neutral-white (4000-
kelvin) full-spectrum (400-750nm). A photosynthetic photonic flux density (PPFD) of
200μmol/m2s was maintained for each of the three cases for an average time-period of
14 hours everyday for 60 days. The 14-hour time-period was determined from the
approximate light exposure time required for plants10. The temperature and humidity
levels in the room were maintained at 25 degrees Celsius and 40 per cent respectively.
The growth patterns of the different plant species were qualitatively observed and
documented over this period based on two stages: germination and vegetation.
Table 1: Photoperiodism requirements of plants in Profile-1
Sr. No:
Plant Species
Photoperiodism
Flowering
1
Lettuce
Day Long
Requires long light hours
2
Parsley
Day Short
Requires short light hours
3
Tomato
Day Neutral
Not related to light hours
86 Amardeep M. Dugar, Manju Dileep, Hussain Burhani
Table 2: Experimental setup and light spectrums of the three cases in Profile-1
Case-A
Blue-Red Spectrums
(460+630+660nm)
Case-C
White Full-spectrum
(400-750nm)
2.2 Materials and Methods Profile-2
A multipurpose room inside a basement office space in the city of Mumbai, India that
did not have any penetration of natural sunlight was selected for this plant-growth
profile. Nine different ornamental plant species as listed in Table-3 were selected
based on their general popularity of use within interior environments from a
preliminary market survey. Two of the most prominently used colour temperatures for
architectural lighting applications within interior environments are: warm-white
(3000-kelvin) and neutral-white (4000-kelvin). Two sets of 2m-long parallel tracks
were mounted on the ceiling with three 30W LED track luminaires from Hazel
Lighting on each track and a total of six luminaires for each set so as to bathe the
space in these two colour temperatures as shown in Table-4. Two identical sets of
these ornamental potted plants were placed under each of these luminaire
arrangements so as to be bathed in the two different colour temperatures: Case-X in
warm-white and Case-Y in neutral-white. The plants were positioned in a manner that
is similar to any natural outdoor environment with a mix of small and large plants so
as to study the effect of the shadow of bigger plants on the life cycles of smaller
plants. An average lux level of 1000lux at a nominal height of 0.75m was maintained
for both cases for an average time-period of 10 hours everyday for 90 days. The 10-
hour time-period was based on the fact the office would be operational for a period of
10 hours from 8:00AM to 7:00PM. The temperature and humidity levels in the room
were maintained at 25 degrees Celsius and 40 per cent respectively.
White LED Light Sources Merging Architectural and Horticultural Lighting 87
Table 3: Plant species in the Profile-2
Dracena
Scindapsus
Syngonium
Zamioculcus
Aglaonema
Calathea
Spathiphyllum
Sansevieria
Bird Nest
Table 4: Experimental setup of the two cases in Profile-2
Design of the multipurpose room with two parallel sets
of track lighting for the two cases
Case-X: Plants in warm-white (3000K)
light
Case-Y: Plants in neutral-white (4000K)
light
A qualitative survey interview questionnaire was designed to assess how the
installation of illuminated ornamental plants impacted the overall views of the
multipurpose room as depicted in Table-5. A total of 25 users (13 from the office, 5
88 Amardeep M. Dugar, Manju Dileep, Hussain Burhani
from the neighbouring offices and 7 regular office visitors) were interviewed twice:
once before, and once 45 days after the installation. The first interview documented
their aspirations about the installation with questions pertaining to: whether they
would like such an installation in their office, if yes why, what kind of plants, and in
what spatial arrangement; whether they will sacrifice some of their workable office
space to accommodate such an installation. The second interview documented their
experience after the installation with questions pertaining to: whether the installation
met their aspirations in terms of the kind of plants and spatial arrangements; whether
they will sacrifice some of their workable office space to accommodate such an
installation; whether the installation provided any improvement in their health,
productivity and wellbeing; and finally their preference for which of the two colour
temperatures for lighting the installation.
Table 5: Office users’ views of Profile-2
View in the multipurpose
room
View of the multipurpose room from the office
3.0 RESULTS AND DISCUSSION
The plant-growth results listed in this section are purely on the basis of qualitative
observations and literature references. Considering the pilot nature of this small-scale
study, no other forms of scientific analysis or assessment has been done.
3.1 Results and Discussion Profile-1
The results of the germination stage for the first profile are outlined in Table-6. Case-
A reported the fastest germination time for lettuce and parsley due to the high content
of red spectrum, which speeds the process. Case-B reported the slowest germination
time for lettuce due to the low content of red spectrum, which slows the process.
Case-C reported an average germination time for lettuce due to the combined
White LED Light Sources Merging Architectural and Horticultural Lighting 89
presence of red and far-red spectrums, where red spectrum speeds the process and far-
red spectrum slows the process. There was no difference in germination time between
all the three cases for tomato.
Table 6: Germination stage results of Profile-1
Case
Germination
Lettuce
Parsley
Tomato
A
Blue-Red
Spectrums
(460+630+660nm)
Time
2 Days
8 Days
5 Days
Reasoning
Fastest germination time for lettuce and parsley
high content of red spectrum speeds
germination process
B
Blue-Red-White
Spectrums
(380-730nm)
Time
3 Days
9 Days
5 Days
Reasoning
Slowest germination time for lettuce and parsley
low content of red spectrum slows germination
process
C
White
Full-spectrum
(400-750nm)
Time
2.5 Days
9 Days
5 Days
Reasoning
Average germination time for lettuce
combined presence of red and far-reds spectrums
balances germination process
The results of the vegetation stage divided under seedling growth, leaf and plant
growth, and growth till blooming for the first profile are outlined in Table-7. Case-A
reported a seedling growth that is slowest for lettuce and parsley, and fastest for
tomato; unhealthiest leaf and plant growth for all three vegetables; and fastest
blooming time for tomato. This can be attributed to the fact that the specific blue-red
spectrum (460+630+660nm) light source has low content of blue spectrum that
diminishes vegetative growth for leafy vegetables like lettuce and parsley; and high
content of red spectrum that leads to elongated and weak stems, increases the inter-
nodal distance, and aids blooming for tomatoes12. Case-B reported a seedling growth
that is average for lettuce and parsley, and slowest for tomato; leaf and plan growth
that is healthy for lettuce and parsley and unhealthy for tomato; and no blooming for
tomato. This can be attributed to the fact that the full-range blue-red-white spectrum
(380-730nm) light source has higher content of blue spectrum that aids vegetative
growth for leafy vegetables like lettuce and parsley; and lower content of red
spectrum that diminishes blooming for tomatoes12. Case-C reported a seedling growth
that is fastest for lettuce and parsley, and average for tomato; healthiest leaf and plant
growth for all three vegetables; and average blooming time for tomato. This can be
attributed to the fact that the full-spectrum (400-750nm) light source has a slightly
better balanced content of all the spectrums than the other cases, which aid vegetative
90 Amardeep M. Dugar, Manju Dileep, Hussain Burhani
growth thereby leading to overall healthy plants10. However the overall growth for
lettuce in all the three cases was much less compared to naturally grown lettuce. This
can be attributed to the fact that all three light sources have a low content of green
spectrum (500-600 nm), which enhances the growth of lettuce plants11.
3.2 Results and Discussion Profile-2
All plants reported good growth and health over the entire 90-day period. All 25
participants (100%) in the survey interview before the installation expressed their
preference plants in the office space. However, only 10 participants (40%) were
willing to sacrifice their space for plants and 20 participants (80%) refused to take any
responsibility for taking care of these plants. In the survey interview after the
installation, 22 participants (88%) were willing to sacrifice their space to
accommodate plants as well as personally take care of these plants. All 25 participants
(100%) confirmed that having plants in their surroundings provided improvements in
their health, productivity and wellbeing. This can be attributed to biophilia, meaning
the beneficial characteristics of the natural world to improve human health,
productivity and wellbeing, in relation specifically to interior ornamental plants13. All
25 participants (100%) confirmed that lighting in terms of lux level was comfortable,
and they preferred neutral-white (4000K) light for the plant installation. This can be
attributed to the fact that neutral-white has the closest property to daylight, which
renders a natural appearance to plants10.
Table 7: Vegetation stage results of Profile-1
Case
Vegetation
Lettuce
Parsley
Tomato
A
Blue-Red
Spectrums
(460+630+660nm)
Seedlings
Growth
Slowest
growth
6mm per day
Slowest
growth 3mm
per day
Fastest growth
18mm per day
Leaf &
Plant
Growth
Slowest but
improper
formation of
leaves
Tallest but
weakest with
slender and
elongated stem
leaning
towards the
light source
Tallest but weak
with slender and
elongated stem
leaning towards
the light source,
and highest inter-
nodal distance
Growth till
Blooming
NA
NA
Fastest blooming
≤ 5 weeks
Reasoning
Low content of blue spectrum diminishes
vegetative growth especially for leafy vegetables
like lettuce and parsley. High content of red
spectrum leads to an elongated and slender stem,
increases the inter-nodal distance, and aids
blooming especially for tomatoes.
White LED Light Sources Merging Architectural and Horticultural Lighting 91
B
Blue-Red-White
Spectrums
(380-730nm)
Seedlings
Growth
Average
growth
9mm per day
Average
growth 6mm
per day
Slowest growth ≤
10mm per day
Leaf &
Plant
Growth
Fastest with
proper
formation of
leaves
Shortest but
healthy with
thick and
sturdy stem,
and large
leaves
Shortest and
weakest with
thinnest stem,
unable stay
upright without
support
Growth till
Blooming
NA
NA
No blooming
Reasoning
High content of blue spectrum aids vegetative
growth especially for leafy vegetables like lettuce
and parsley. Low content of red spectrum
diminishes blooming for tomatoes.
C
White
Full-spectrum
(400-750nm)
Seedlings
Growth
Fastest
growth
12mm per
day
Fastest growth
≤ 9mm per day
Average growth
≤ 12mm per day
Leaf &
Plant
Growth
Average but
formation of
largest and
healthiest
leaves
Average but
healthiest with
thickest and
sturdiest stem,
and largest
leaves
Average but
healthiest with
thick and sturdy
stem, and largest
leaves
Growth till
Blooming
NA
NA
Average
blooming 6
weeks
Reasoning
Continuous spectrum with appropriate blue
content aids vegetative growth for leafy
vegetables like lettuce and parsley, red content
aids blooming for tomatoes, and other spectral
contents such a green ensures better overall health
of all three plants.
4.0 CONCLUSION
The overall observations of both plant-growth profiles reveals that plants can be
installed and maintained in interior environments with white LED light sources used
for architectural lighting applications. However, the horticulture industry seems to
have overlooked the use of white light because it was believed that plant illumination
92 Amardeep M. Dugar, Manju Dileep, Hussain Burhani
should emit mostly blue and red light as it is assumed they provide the most effective
photosynthesis reaction. But precise and independent measurements of photosynthetic
activity under different wavelengths have demonstrated that the green spectrum (500-
600nm) is nearly as effective as blue spectrum for a considerable number of plant
species12. Additionally, the green light would make the plant leaves appear green and
normal, similar to a natural setting under white light, thereby offering psychological
benefits for humans11. Therefore for plants grown purely under artificial lighting,
which can impact their visual appearance and biological function, it is advisable to
consider the characteristics of broad-spectrum solar radiation via LED lighting
technology10. As the optical characteristics of luminaires used for humans and plants
in this small-scale pilot study are similar, it is possible to design lighting for both
architectural and horticultural applications.
ACKNOWLEDGEMENTS
The authors thank Hazel Lighting and Ruud Lighting for technical support during the
experimental procedures.
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94 Amardeep M. Dugar, Manju Dileep, Hussain Burhani
... Measurable improvements to the human condition in terms of health, well-being and productivity have been reported by the use of green elements such as green walls in interior environments [7]- [11]. Robust This small-scale qualitative pilot study argues that white LEDs normally used for architectural lighting applications offering all the main bands of wavelengths in the photosynthetically active radiation (PAR) spectrum (390-700 nm) enable plant-growth at an appropriate biological speed, while rendering a natural visual appearance to green walls within interior environments [22]. Photosynthetic photon flux (PPF) derived from the total amount of PAR has the most effect on plant growth as more PPF means more photons and more power, and is a parallel to lumens. ...
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