The role of glass as a barrier against the transmission of ultraviolet radiation: An experimental study

Abstract

Excessive exposure of the skin to sunlight may cause many symptoms and skin cancer. The aim was to measure the transmission of ultraviolet (UV) A and UVB radiation through glasses of different types, according to the distance from the light source.
The baseline radiation from UVA and UVB sources was measured at different distances from the photometers. Next, the radiation from the same sources was measured at the same distances, but transmitted by different types of glass. The baseline values were compared with the results after protection using glass.
Laminated glass totally blocked UVA radiation, while smooth ordinary glass transmitted the highest dose (74.3%). Greater thicknesses of glass implied less radiation transmitted, but without a significant difference. Green glass totally blocked UVA radiation, while blue glass transmitted the highest dose of radiation (56.8%). The presence of a sunlight control film totally blocked UVA radiation. All glasses totally blocked UVB radiation.
The main characteristics of glass that make it a photoprotective agent are its type (especially laminated glass) and color (especially green), which give rise to good performance by this material as a barrier against the transmission of radiation.

Full text

ORIGINAL ARTICLE
The role of glass as a barrier against the transmission of ultraviolet
radiation: an experimental study
Ida Duarte, Anita Rotter, Andrey Malvestiti & Mariana Silva
Department of Dermatology, Santa Casa de Miseric ´
ordia de Sa
˜o Paulo, Sao Paulo, Brazil
Key words:
glass; radiation; sunlight; ultraviolet rays
Correspondence:
Ida Duarte, Department of Dermatology, Santa Casa
de Miseric´ordia de Sa
˜o Paulo, Rua Monte Alegre,
523/101, Sao Paulo 05014-000, Brazil.
Tel: 155 11 3871 4018
Fax: 155 11 3871 4018
e-mail: idaduarte@terra.com.br
Accepted for publication:
25 February 2009
Conflicts of interest:
None declared.
Summary
Background/Purpose: Excessive exposure of the skin to sunlight may cause many symptoms
and skin cancer. The aim was to measure the transmission of ultraviolet (UV) A and UVB
radiation through glasses of different types, according to the distance from the light source.
Methods: The baseline radiation from UVA and UVB sources was measured at different
distances from the photometers. Next, the radiation from the same sources was measured at
the same distances, but transmitted by different types of glass. The baseline values were
compared with the results after protection using glass.
Results: Laminated glass totally blocked UVA radiation, while smooth ordinary glass
transmitted the highest dose (74.3%). Greater thicknesses of glass implied less radiation
transmitted, but without a significant difference. Green glass totally blocked UVA radiation,
while blue glass transmitted the highest dose of radiation (56.8%). The presence of a
sunlight control film totally blocked UVA radiation. All glasses totally blocked UVB radiation.
Conclusion: The main characteristics of glass that make it a photoprotective agent are its type
(especially laminated glass) and color (especially green), which give rise to good
performance by this material as a barrier against the transmission of radiation.
The effects on the skin from short- and long-term exposure
to ultraviolet (UV) radiation have already been extensively
dealt with in the literature (1–4). The main acute effects are
erythema, feelings of heat, edema, pain and pruritus. Other
events include late bronzing, thickening of the epidermis and
dermis, immunosuppression and vitamin D synthesis. On the
other hand, the chronic effects of this exposure consist of early
aging of the skin and carcinogenesis (5–7).
Nowadays, huge amounts of time in our daily lives are spent
in closed environments and in vehicles. Although the adverse
effects of UV radiation are well known, the function of the glass
for photoprotection has little coverage in the literature (8–10).
Recent advances in the glass industry have resulted in the
manufacture of window glass that provides broad protection
against UV radiation, but without causing losses in visible light
transmission. Some characteristics of glass material may have an
influence on the properties of protection against UV radiation,
such as the type, color, layers and coating of the glass (9).
Clear ordinary glass: This is transparent and colorless. Its main
characteristic is its capacity to provide protection against the
outside elements, while at the same time allowing transmission
of visible light into the interior. Depending on the thickness,
clear glass can transmit 490% of visible light (between 400 and
780 nm) and up to 83% of solar heat (9). It is also possible to
obtain imprinted glass by means of continuous melting of the
vitreous mass. Metal rollers are used to print a wide variety of
textures onto its surface.
Laminated glass: This is produced by associating two laminae of
glass with a layer of plastic (PVB – polyvinyl butyral), under heat
and pressure. Once the glass-and-plastic composite has been cast,
the result is a single lamina that is generally very similar to clear
ordinary glass. The benefit of laminated glass is that, if it breaks,
the fragments continue to adhere to the PVB layer, instead of
becoming scattered, thereby reducing the risk of accidents. PVB
filters approximately 99% of UV radiation without diminishing
the transmission of visible light (9).
Tempered glass: This is obtained by gradually heating the glass
and then abruptly cooling it in a vertical or a horizontal
tempering furnace. This is essentially a type of safety glass. In
the event of breakage, it shatters into very small pieces that are
not sharp (9).
Variation in the thickness of the glass has limited influence
with regard to blocking UV radiation, according to studies (9).
Tinted glass contains special colored components that absorb up
to 50% of the incident solar energy, thereby reducing the
undesired heat gain and transmitting less UV and visible light, in
comparison with ordinary glass (9). A study on the penetration
of UV radiation through car window glass demonstrated that this
transmission depended on whether the glass was tinted or not.
The results demonstrated that the colored sample completely
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removed the UVB spectrum and only allowed a small proportion
of UVA to pass (10).
UV transmission through vehicle window glass depends on
the type and tinting of the glass. For safety reasons, all
windscreens are made of laminated glass, which is able to filter
out practically all of the UVA. However, the glass for the side and
rear windows is normally tempered and therefore some of the
radiation is able to pass through. Plastic film to control sunlight,
which is often applied to these windows, results in 20–35%
visibility (transmission of visible light) and filters out the UVA of
wavelengths o380–370 nm (9).
The aim of the present study was to measure the transmission
of UVA and UVB radiation through samples of various types of
glass used in the windows of vehicles and houses, taking into
consideration the following variables: type, thickness and color
of the glass, application of sunlight control film and distance
between the light source and the glass.
Materials and methods
The following materials were used in the experiment:
(1) Glass
a. Window glass from built environments, with the following
variables: type (smooth ordinary, imprinted ordinary,
tempered and laminated), thickness (from 0.4 to 0.8 cm)
and color (colorless, green, wine, yellow and blue).
b. Window glass from vehicles, taking into consideration the
type (laminated and tempered) and application of sunlight
control film of the brand Insulfilm
TM
, type G50 (which
allows 50% visibility).
(2) Handisol
TM
UVA(315–400nm) and UVB(280–320nm)
emission sources, UVA-400C (315–400nm) and UVB(280
–320nm) photometers and goggles for protection against
UV radiation, all manufactured by National Biological
Corporation (Beachwood, OH, USA).
Firstly, the baseline radiation from the UVA emission source
was measured. This was measured after the source had been
switched on for 15 min, at distances of 0, 25, 50 and 100 cm,
without any glass as a barrier. The same procedure was then
followed using the UVB emission source.
The transmission of UVA and UVB radiation was then
measured through the different glass samples, taking the
following variables into consideration: type, thickness and color
of the glass, application of sunlight control film and distance
from the light source to the glass, up to the distance of 50 cm.
Lastly, the percentages of radiation transmitted through the glass
were calculated from the baseline values, thereby allowing these
materials to be evaluated as photoprotection agents.
Results
From the measurements of baseline radiation from the UVA
emission source, it was found that the initial radiation at the
distance of 0 cm from the photometer was 7.4 W/cm
2
; it was
0.6 W/cm
2
at 25 cm; 0.1 W/cm
2
at 50 cm; and no radiation was
detected by the photometer at 100 cm. UVB radiation without
glass protection gave the following results: 0.92 mW/cm
2
at
0 cm; 0.06 mW/cm
2
at 25 cm; 0.01 mW/cm
2
at 50 cm; and no
radiation was detected by the photometer at 100 cm.
In measuring the intensity of the radiation from the UVA
source, a considerable reduction in the quantity detected by the
photometer was observed as it was moved away from the source.
At a distance of 25 cm, the measurement was 0.6 W/cm
2
, which
corresponded to only 8% of the baseline UVA. This signifies a loss
of 92% of the irradiation when the measuring instrument was
moved away. With the photometer at a distance of 50cm, 0.1 W/cm
2
was detected, corresponding to 1.3% of the UVA radiation
transmitted by the source.
Tables 1–4 show the radiation detected by the photometer
after introducing the protective barriers of glass. With regard to
the types of glass used in buildings (Table 1), it was found that
laminated-glass totally blocked the UVA radiation, independent
of the distance from the source. At 0 cm from the source, smooth
ordinary glass was the type that transmitted the greatest amount
of radiation (74.3%), followed by tempered glass (71.6%) and
imprinted glass (44.6%). At a distance of 50 cm, all four samples
totally blocked the radiation.
Analysis of the smooth ordinary glass alone (Table 2) showed
that greater thicknesses blocked the passage of radiation more,
but without reaching statistical significance. At a distance of
50 cm, all the samples of smooth ordinary glass totally blocked
the radiation.
With regard to the color of imprinted ordinary glass (Table 3),
it was found that green glass totally blocked the UVA radiation,
independent of the distance from the source. At 0 cm from the
source, blue glass transmitted the greatest dose of radiation
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Table 1. Radiation from UVA emission source that was transmitted by different types of glass, according to distance from source
Type of glass
Radiation transmitted according to distance from source
0 cm (7.4 W/cm
2
) 25 cm (0.6 W/cm
2
) 50 cm (0.1 W/cm
2
)
W/cm
2
% W/cm
2
% W/cm
2
%
Smooth ordinary glass (4 mm) 5.5 74.3 0.4 66.6 0 0
Imprinted ordinary glass (4 mm) 3.3 44.6 0.3 50 0 0
Tempered glass (4 mm) 5.3 71.6 0.4 66.6 0 0
Laminated glass (8 mm) 0 0 0 0 0 0
Q2
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(56.8%), followed by colorless (36.5%), wine (31.1%) and
yellow (1.3%). Once again, at 50cm, all the samples analyzed
totally blocked the emitted radiation.
With regard to UVB radiation, for all the variables analyzed
(type, thickness and color of the glass), it was observed that the
samples totally blocked the UVB radiation at any distance from
the emission source.
Among the types of vehicle window glass (Table 4), it was
found that laminated glass totally blocked UVA radiation,
independent of the distance from the source. Tempered glass
for vehicle win dows transmitted 17 .6% of the radiation at 0 cm
from the source and totally blocked the radiation at greater
distances. Application of G50 sunlight control film to the
tempered glass totally blocked the UVA radiation emitted by
the source.
For all the variables analyzed (type of glass and application of
G50 sunlight control film), it was observed that the samples
totally blocked the UVB radiation, at any distance from the
emission source.
Discussion
Some studies have reported the importance of glass for blocking
UVB radiation and a certain wavelength range of UVA radiation (2).
Others have proven the importance of glass as a photoprotective
agent against undesirable biological effects. Bernstein et al.(8)
demonstrated that the decreased transmission of UV radiation
caused by glass drastically reduced the cytotoxicity measured using
the neutral red uptake photoprotection assay. However, little is
known about the influence of each characteristic of glass samples
on photoprotection (such as the type, thickness and color of the
glass and, in the case of vehicles, the application of sunlight control
film) and the impact of these effects on different skin phototypes.
In the present study, it was observed that all of the types of
glass decreased the transmission of UVA. Glass of laminated type
was the most efficient for totally blocking the UV radiation. This
may be explained by its production characteristics: an association
between two glass laminae and a layer of plastic (PVB), which
makes it an effective barrier against UVA (9).
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Table 2. Radiation from UVA emission source that was transmitted by smooth ordinary glass of different thicknesses, according to distance from source
Thickness of smooth
ordinary glass (cm)
Radiation transmitted according to distance from source
0 cm (7.4 W/cm
2
) 25 cm (0.6 W/cm
2
) 50 cm (0.1 W/cm
2
)
W/cm
2
% W/cm
2
% W/cm
2
%
0.2 5.6 75.7 0.5 83.3 0 0
0.3 5.5 74.3 0.4 66.6 0 0
0.4 5.5 74.3 0.4 66.6 0 0
0.5 4.7 63.5 0.4 66.6 0 0
0.6 4.5 60.8 0.4 66.6 0 0
0.8 3.8 51.4 0.3 50 0 0
1.0 3.8 51.4 0.3 50 0 0
Table 3. Radiation from UVA emission source that was transmitted by imprinted ordinary glass of different colors, according to distance from source
Color of imprinted ordinary glass
Radiation transmitted according to distance from source
0 cm (7.4 W/cm
2
) 25cm (0.6 W/cm
2
) 50cm (0.1 W/cm
2
)
W/cm
2
% W/cm
2
% W/cm
2
%
Colorless (3 mm) 2.7 36.5 0.2 33.3 0 0
Blue (3 mm) 4.2 56.8 0.3 50 0 0
Wine (3 mm) 2.3 31.1 0.2 33.3 0 0
Yellow (3 mm) 0.1 1.3 0 0 0 0
Green (3 mm) 0 0 0 0 0 0
Table 4. Radiation from UVA emission source that was transmitted by vehicle window glass of different types, according to distance from source
Type of glass
Radiation transmitted according to distance from source
0 cm (7.4 W/cm
2
) 25 cm (0.6 W/cm
2
) 50 cm (0.1 W/cm
2
)
W/cm
2
% W/cm
2
% W/cm
2
%
Tempered vehicle window glass (3 mm) 1.3 17.6 0 0 0 0
Tempered vehicle window glass with G50
protective film
000 00 0
Laminated glass (8 mm) 0 0 0 0 0 0
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The differences related to the UVA-laminated glass transmition
may be explained by the different manufacturers and the
technique utilized to obtain the measures. But as we know the
laminated glass is efficient to protect from the UVA radiation (9).
Some works published showed that the UV exposition through
car or home windows may favor the skin damage with the
windows opened, without the presence of glass protection
(11–13).
The transmission of radiation decreased with increasing
thickness of the glass, but not significantly, thus demonstrating
that this variable has little influence on blocking the radiation, in
comparison with the other variables analyzed. On the other
hand, the color of the glass had a huge influence on the
transmission of radiation. The sample of green glass totally
blocked the radiation and yellow glass only allowed the passage
of 1.3%, which may have occurred because of the properties of
the tinting pigments present. In glass manufacturing, colored
additives can be used, such as Fe
31
, which confers a brownish
yellow color, or a mixture of Fe
31
and Fe
21
, which provides a
green color. The Fe
21
ion absorbs light in the infrared region,
while Fe
31
absorbs light in the UV region. Thus, samples
containing Fe
31
in the tinting pigment are more efficient in
diminishing the transmission of UVA (14).
As already demonstrated in other studies, application of a
protective film to vehicle window glass gives rise to lower UVA
transmission than in the window glass alone (9). The results
from the present study demonstrated that the glass with the G50
sunlight control film totally blocked the UVA radiation.
The UVB radiation was totally blocked in the presence of all of
the glass samples used, at any distance from the emission source,
because its power of penetration is lower than that of UVA (2). It
can be affirmed that glass is an excellent filter for this type of
radiation, independent of its type, thickness or color.
Furthermore, the distance of the glass from the emission
source significantly influenced the quantity of baseline
radiation, such that the greater the distance, the lower the
irradiation and therefore the lower the transmission of UV
through the glass. This may be explained by the huge
dissipation of energy that occurs at greater distances under
environmental conditions.
Applying the above results to a situation within day-to-day
life, the UVB radiation incident on an individual inside a car with
closed windows is zero. Even in the case of UVA radiation, the
transmission would be insufficient to produce actinic damage,
given that not only does the glass block a large proportion of the
radiation but also small changes in the distance from the
emission source significantly decrease the irradiation.
Therefore, internal environments protected by glass can be
considered safe with regard to photoprotection. This observation
is also important within the field of occupational medicine, in
which the use of glass in vehicles used professionally would be a
preventive health measure for workers. Even taking into account
the radiation produced by artificial light bulbs within closed
environments, such as homes and offices, there is no risk of
phototoxicity. Even if these bulbs transmit some quantity of UV
radiation, this radiation is blocked by the glass of the light bulb
or the lamp itself, along with the distance between the source and
the individual.
It can be inferred that window glass may act as a photopro-
tective agent to prevent skin damage, by blocking the
transmission of UV radiation. This conclusion has a positive
impact on society, given that this material has a constant presence
in day-to-day life because of its versatility. The use of glass within
the fields of architecture, civil construction and the car industry
implies optimization of care relating to photoprotection.
There is a new type of glass called UV-blocking coated glass
(9). It is almost indistinguishable from standard clear glass and
blocks 498% of UV radiation while transmitting all the visible
light. It can be combined with a variety of other glass products,
often resulting in nearly complete UV blockage. This show the
industry’s concern for human health.
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