ArticlePDF Available

Abstract and Figures

Solar protection is an important public health issue because solar UV exposure can cause acute and chronic damage in skin. Seeking shade is a convenient and commonly practiced sun avoidance measure. Shade works by physically shielding skin from direct UV rays; however UV rays can also reach skin from other angles. It is not clear how protective are the widely-used shade structures like umbrellas and walls under actual use conditions. In this study, a sky view model was applied to systematically assess the influence of different factors to umbrellas and walls, including the transmission of the shade materials, the reflectivity of the ground or the wall, diffused UV to total UV irradiance ratio, shade geometry, a person’s positions and orientations in the shade. We measured the sunburn protection factor (SPF) with a calibrated UV meter at different positions in the shades of umbrella at different times of the day and compared the measurement results to the modeling. We found that shade structures like umbrellas and walls are more effective when the ratios of diffused UV to total UV irradiance are smaller (mid-day). The effectiveness increases with more coverage, less surface reflectance, and more centralized positions in the shade. The SPF value for a typical umbrella, is probably between 3 and 7 in real-life. The low sun protection level offered by a typical shade highlights the importance of educating the public about how to properly protect skin from the sun and the importance of applying a combination of sun protection measures during extended sun exposures.
Content may be subject to copyright.
Photochemical &
Photobiological Sciences
PAPER
Cite this: Photochem. Photobiol. Sci.,
2017, 16, 1537
Received 9th June 2017,
Accepted 10th August 2017
DOI: 10.1039/c7pp00214a
rsc.li/pps
Sun protection by umbrellas and walls
Hao Ou-Yang * and Thomas Shyr
Solar protection is an important public health issue because solar UV exposure can cause acute and
chronic damage to the skin. Seeking shade is a convenient and commonly practiced sun avoidance
measure. Sha de works by physically shielding the skin from direct UV rays; however UV rays can also
reach the skin from other angles. It is not clear how protective the widely-used shade structures like
umbrellas and walls are under actual use conditions. In this study, a sky view model was applied to
systematically assess the inuence of dierent factors to umbrellas and walls, including the trans-
mission of the shade materials, the reectivity of the ground or the wall, d iused UV to total UV ir-
radiance ratios, shade geometry, a persons positions and orientations in the shade. We measured the
sunburnprotectionfactor(SPF)withacalibratedUVmeteratdierent positions in the shades of an
umbrella at dierent times of the day and compared the measurement results with the modeling. We
found that shade structures like umbrellas and walls are more eective when the ratios of diused
UV to total UV irradiance are smaller (mid-day). The eectiveness increases with more coverage , less
surfac e reectance, and more centralized positions in the shade. The SPF value for a typical umbrella
is probably between 3 and 7 in real-life. The low sun protection level oered by a typical shade high-
lights the importance of educating the public about how to properly protect the skin from the sun
and the importance of applying a combination of sun protection measures during extended sun
exposures.
Introduction
UV exposure from the sun may induce erythema, pigmenta-
tion, pre-mature skin aging, and skin cancer. Since many of
these conditions can be prevented or delayed by reducing sun
exposure, it is critical for the public to employ appropriate sun
protection measures, especially during extended outdoor
periods. Commonly practiced sun avoidance measures include
limiting the time under the sun during mid-day (when the UV
index is higher than 3); wearing cover-up clothes and hats;
applying broad spectrum sunscreen, and seeking shade. Shade
works as a physical barrier between the sun and the skin
surface to shield direct UV rays. However, studies have shown
that there is a significant diuse component in the UV radi-
ation in the environment
14
that may reach the skin outside
the angles covered by shade structures.
There is a lack of standard metrics for protection by shade
vs. the sun protection factor (SPF) for sunscreen and the ultra-
violet protection factor (UPF) for cloth. Measurements show
that the UV intensity diers significantly in various shades.
59
Factors including the transmission of the shade material, the
geometry of the shade and diuse UV irradiance can all sig-
nificantly aect the measurement and lead to dierent protec-
tion levels.
1,911
Because shade not only blocks UV rays but also visible
and infrared rays, it provides a desirable cooling eect for
outdoor activities and a false impression that most rays are
suciently blocked while staying in the shade. This false
sense of security and the lack of a clear understanding about
the protection a shade structure may provide under actual use
conditions can lead to significant over exposure. In this study,
we applied a sky view model developed by Utrillas et al.
12,13
to
systematically assess how dierent factors can impact the pro-
tection levels of typical shades. We hope to gain quantitative
knowledge of the range of protection a typical shade structure
may achieve and how the protection varies with dierent
parameters.
Shade structures can be viewed as either one of the two
basic types or the combination of the two types: (a) the shade
structures present over a person, such as beach umbrellas,
trees, or canopies, and (b) the shade structures present beside
a person, including buildings, walls, sidings etc. We focused
on discussing the first type and used umbrellas as an example
for experimental validation. A similar approach is also applied
to simulate wall shades.
Johnson and Johnson Consumer Inc., Skillman, NJ 08558, USA.
E-mail: houyan4@its.jnj.com; Tel: +(908)-874-2722
This journal is © The Royal Society of Chemistry and Owner Societies 2017 Photochem. Photobiol. Sci.,2017,16,15371545 | 1537
Materials and methods
Sky view model for an umbrella
For the umbrella shade, when a person lies down under the
umbrella as demonstrated in Fig. 1a, the UV rays that reach
the horizontal skin surface (I
horizontal
) can be divided into two
parts: irradiance that goes through the umbrella (I
umbrella
) and
irradiance that is unobstructed from the sky (I
sky
). SVF (sky
view factor) represents the projected area on the unit sphere
detector that corresponds to the unobstructed rays relative to
the whole detection area (π). UVF (umbrella view factor)
represents the projected area (as a percentage of π) that is
related to the rays passing through the umbrella. By definition
SVF + UVF = 1.
Ihorizontal ¼Isky ðSVFhorizontal ÞþIumbrella ðUVFhorizontal Þ
¼Idiffuse ð1sin2θÞþIdiffuse sin2θtr þIdirect tr:
ð1Þ
I
umbrella
is aected by the transmission (tr) of the umbrella
and includes both diuse UV and direct UV components,
referred to as I
diuse
and I
direct
above. The coverage of the
umbrella in this case is characterized by sin
2
θand θ= arctan
(R/H), where Rand Hare the radius of the umbrella and the
distance between the skin and umbrella plane (i.e. the
umbrella height).
When the skin surface is perpendicular to the ground or
the umbrella plane (Fig. 1b), the UV intensity (I
vertical
), based
on the incident angles, can be divided into SVF, UVF and GVF
(ground view factor), since UV can now also be reflected from
the ground. GVF is 0.5 in this case because ground reflectance
makes up 50% of the projected area on the detector. We have
SVF = 0.5 UVF.
Ivertical ¼Iumbrella ðUVFvertical ÞþIsky ðSVFverticalÞ
þIground ðGVFvertical Þ¼Idiffuse ðUVFvertical Þ
tr þIdirect tr þIdiffuse ð0:5UVFvertical Þ
þIdiffuse albedoground 0:5
ð2Þ
where ground albedo (albedo
ground
) and umbrella transmission
(tr) have been incorporated. The UVF
vertical
for this scenario
can be written as a function of Rand Hof the umbrella
(Fig. 1c).
UVFvertical ¼1=πðφ¼acrtan R
H
ðÞ
φ¼0ð1ðcos βÞ2Þdφ
and
β¼acrtan Rsin α
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
H2þðRcos αÞ2
q
0
B
@1
C
Aand tan φ¼Rcos α
Hð3Þ
When the umbrella has a circular shape UVF
vertical
can be
simplified as
UVFvertical ¼1=πðarctanðR=HÞ0:5sinð2arctanðR=HÞÞÞ
ð4Þ
The protection factor (PF) for the umbrella can then be
defined as
PFðhorizontalÞ¼Ihorizontal=Itotal and PFðverticalÞ¼Ivertical =Itotal
ð5Þ
Since I
total
=I
diuse
+I
direct
and I
horizontal
or I
vertical
is a func-
tion of I
diuse
, it becomes clear that PF is a function of R/H
(parameter for coverage), tr (umbrella transmission), ground
albedo, and the diuse UV to total UV irradiance ratio (dr),
where dr = I
diuse
/I
total
. We noted that this model is based on
the person located at the center under the umbrella. A scen-
ario when the person is located away from the center under
the umbrella is discussed in the Appendix.
Sky view model for a wall
Horizontal PF. When a person is facing up on the ground
positioned at a distance Dfrom the middle width of a wall
(height = H, width = W, Fig. 2a), UV photons can reach the skin
directly from the sky or through reflectance from the wall (we
assume that the wall has no UV transmission but can reflect
light). We can write the reflectance section (wall view factor or
Fig. 1 Beach umbrella as shade: (a)-top: the subject lies down under
the umbrella with the skin surface facing up to the umbrella plane (hori-
zontal orientation). Ris the umbrella radius and His the distance
between the skin surface and umbrella plane. θ= arctan(R/H)denes
the coverage angle of the umbrella. UVF and SVF are the projected areas
on the plane of the unit sphere detector; (b)-bottom: the subject stands
up under the umbrella with the skin surface facing sideways (vertical
orientation). The angles α,ϕ, and βindicate respectively the variables on
the umbrella plane, the projected detection plane, and the plane that is
perpendicular to the umbrella plane. UVF, SVF and GVF are the umbrella
view factor, sky view factor and the ground view factor.
Paper Photochemical & Photobiological Sciences
1538 |Photochem. Photobiol. Sci.,2017,16, 15371545 This journal is © The Royal Society of Chemistry and Owner Societies 2017
WVF
horizontal
) like in the case of vertical UVF for the umbrella
as
WVFhorizontal ¼1
πðα¼tan1W=2
D
α¼0ð1R2Þdα;
R¼cos β¼cos tan1H
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
D2þx2
p

ð6Þ
where x=D× tan αis a variable on the Wdirection and βis
the projection angle. We use albedo
wall
to indicate the
reflectivity of the wall surface and can write irradiance in the
shade as
Iwall;horizontal ¼Idiffuse ð1WVFhorizontal ÞþIdiffuse
WVFhorizontal albedowall ð7Þ
Vertical PF. The total UV irradiance for vertical orientation
(I
wall, vertical
) facing a wall (height = H, width = W, distance = D)
is the sum of the irradiances from the sky (I
sky, vertical
), irradi-
ance reflected from the wall (I
wall reflectance, vertical
), and irradi-
ance reflected from the ground (I
ground, vertical
). The weights of
these 3 components are characterized by SVF, WVF and GVF
respectively.
Iwall;vertical ¼Idiffuse SVFvertical þIdiffuse WVFvertical
albedowall þIdiffuse GVFvertical albedoground
ð8Þ
The WVF
vertical
can be divided into 4 regions (Fig. 2c).
WVF1 ¼1
2πðθ¼tan1Ha
B
θ¼0
cos tan1Dcos θ
B

2
dθ
WVF2 ¼1
2πðθ¼π
2
θ¼tan1Ha
B
cos tan1Dsin θ
Ha

2
dθ
WVF3 ¼1
2πðθ¼tan1Hb
B
θ¼0
cos tan1Dcos θ
B

2
dθ
WVF4 ¼1
2πðθ¼π
2
θ¼tan1Hb
B
cos tan1Dsin θ
Hb

2
dθ
WVFvertical ¼2 WVF1 þWVF2 þWVF3 þWVF4ðÞ
ð9Þ
where B=W/2. H
a
or H
b
refers to the height of the wall above
or below the skin position (Fig. 2b).
Since SVF
vertical
is only from the top half and GVF
vertical
is
only from the bottom half, we have
SVFvertical ¼0:52ðWVF1 þWVF2Þ
GVFvertical ¼0:52ðWVF3 þWVF4Þð10Þ
Measurement of the umbrella SPF
The UV transmission of a range of commercial umbrellas was
measured by using a UV spectrophotometer (UV-1000S from
LabSphere, North Sutton, NH), and we found that the trans-
mission of the umbrella materials varies from 0.01% to 10%.
For outdoor PF measurement, we selected an umbrella with
0.1% transmission throughout the UV spectrum. We therefore
assume tr = 0 in the model for this umbrella. The radius of the
Fig. 2 (a) Side view (left) and top view (right) of shade projection on a
horizontal surface of the unit sphere detector by a wall of height Hand
width W, and positioned at distance Dfrom the wall. (b) Side view of a
person standing at a distance Dfrom a wall of heights (H
a
above and H
b
below the point of interest). The detected irradiance on the skin surface
is from the sky, from the diuse irradiance reected othe wall, and the
reected diuse irradiance from the ground. (c) Top, front view of a half
unit sphere detector facing a wall at a distance D. The half width of the
wall is B=W/2. The height of the wall is dened by H
a
and H
b
as in
Fig. 2b. The angle θhelps dene the edge of the wall and can be divided
into four regions. Bottom, side view of the wall projected on the
detector.
Photochemical & Photobiological Sciences Paper
This journal is © The Royal Society of Chemistry and Owner Societies 2017 Photochem. Photobiol. Sci.,2017,16,15371545 | 1539
umbrella was 50 cm. Two dierent positions under the
umbrella were tested: R/H= 1 which corresponds to position-
ing the detector at 50 cm under the umbrella plane (typical
coverage) and R/H= 2 corresponding to 25 cm under the
umbrella plane (excellent coverage).
We measured the UV irradiance by using a calibrated
erythema UV meter (Model 3D v.2 from Solar Light, Glenside,
PA) on three separate cloudless days (May 29
th
to May 31
st
2012) at two open parking lots close to the Los
Angeles International Airport (latitude 33.9
°
N). The output
of the detector was a UV intensity weighted by the CIE erythe-
mal action spectrum (MED per h). The detector was
either facing up or facing sideways for horizontal or vertical
orientations, respectively, under the umbrella for R/H=1or
R/H= 2 coverage. The total UV irradiance was measured
hourly by holding the meter horizontally at a height of 1.9 m.
The ratio of total UV irradiance over the UV
irradiance under the umbrella was considered as the SPF of
the umbrella. On each of the three days, we measured the UV
irradiance throughout the day from 8 AM to 5 PM (with the
solar zenith angle ranging from around 12 to 68 degrees). We
made several readings within each hour period and averaged
all the data collected on dierent days and at dierent
locations but within the same hour and with the same
R/Hcoverage.
The UV ground albedo of the parking lots (the two
parking lots having similar asphalt surfaces) was measured
by using the same erythemally weighted UV meter following
the procedure outlined in the literature.
14
We determined
that the ground albedo is close to 0.06 for these ground
surfaces. We didnt measure directly the diuse component
of the erythemal UV irradiance for these days, and we lever-
aged the data reported in the National Solar Radiation
Database for Los Angeles (NSRDB, 19912005 typical meteo-
rological year data http://rredc.nrel.gov/solar/old_data/nsrdb/
1991-2005/tmy3/by_state_and_city.html). For each hour of
the day, diuse solar irradiance to global solar irra-
diance ratios from dierent months were averaged. Since the
ratios are not erythemally weighted and not specific to UV
wavelengths, they were only used as estimates for modeling
dr.
The same experiment was repeated on June 21, 2012 from
10 AM to 4 PM (with the solar zenith angle ranging from
around 10.7 to 54.0 degrees) at one of the parking lots for both
the R/H= 1 and R/H= 2 positions. This time, we fixed a few
variables that we didnt account for previously: (a) we fixed the
height of the detector from the ground in all the measure-
ments to about 1.6 m; (b) we fixed the orientation of the detec-
tor for vertical measurement (always facing north); (c) we con-
ducted all four measurements (R/H= 1 and = 2 for vertical and
horizontal, respectively) at the same time and at the same
location; and (d) we avoided any direct UV for measurements
under the umbrella as much as possible. When the trans-
mission of the umbrella is negligible, based on eqn (1) and (2)
we can experimentally determine the erythemally weighted
diuse UV to total UV irradiance ratio (dr) at dierent times of
the day (t) for either horizontal (H) or vertical (V) orientation
as:
Erythemal drðHorV;tÞ¼
IR
H¼1;HorV;t

IðR=H¼2;HorV;tÞ
SVF R=H¼1;HorVðÞSVFðR=H¼2;HorVÞ½Iðtotal;tÞ
ð11Þ
The numerators in eqn (11) are the I
horizontal
or I
vertical
values of the two coverage scenarios and were measured at the
same time and same orientation under the umbrella. The
corresponding sky view factors (SVF) in the denominators
solely depend on the R/Hvalues of the umbrella. The I
total
value in the denominators was also measured at the same
time in the same experiment.
Results
Results from modeling
Fig. 3ad show the PFs of an umbrella under dierent scen-
arios. When the skin is positioned horizontally (i.e. facing up,
Fig. 3a), PF increases with the R/Hratio (coverage) and
decreases monotonically with dr. For a typical umbrella cover-
age such as R/H= 1, the PF varies approximately from 3 to 7
for dr ranging from 0.3 to 0.7. The calculations assume tr = 0
and the PF decreases significantly when tr starts to increase
from zero (data not shown). When skin is positioned vertically
(i.e. facing sideways, Fig. 3bd), the PF also increases with the
coverage and decreases with dr. For a typical coverage of R/H=1,
the vertical PF varies approximately from 2 to 8. In addition, ver-
tical PF decreases with the surfaces of higher albedo. Fig. 3bd
show the vertical PFs with the albedo values of 0, 0.05 (resem-
bling asphalt surfaces), and 0.9 (resembling snow-covered
ground). The impact of increasing the ground albedo from 0 to
0.05 is small, but the impact of the ground reflection on the ver-
tical PF can be significant when the ground is highly reflective.
The influence of the position under the umbrella on the PF is
depicted in Fig. 4, in which xrepresents the distance (as a per-
centage of radius R) away from the central position. A detailed
geometric model for this case can be found in the Appendix.
Both the UVF
horizontal
and the horizontal PF decrease signifi-
cantly with x, indicating that the movement and o-center
locales under the umbrella have a strong negative influence on
the coverage and protection level oered by the umbrella.
The horizontal PF values of the walls were simulated with
four scenarios (Table 1): wall albedo at 0.03 or 0.12 and dr at
0.3 or 0.5. It has been reported that the diuse component of
erythemal UV radiation in a cloudless day is around 50% on
average
4
so the two dr ratios represent both a typical and an
extreme (mid-day, more direct light) situations. The PF
increases only slightly with H/Dand W/Das shown in Table 1.
This is because even when the wall is infinitely high and
wide, the side of the detector that is away from the wall will
always be exposed and the maximum WVF
horizontal
is only
Paper Photochemical & Photobiological Sciences
1540 |Photochem. Photobiol. Sci.,2017,16, 15371545 This journal is © The Royal Society of Chemistry and Owner Societies 2017
approaching 0.5 (eqn (6)). The maximal horizontal PF will be
1/(dr × 0.5), assuming that albedo
wall
= 0. We have confirmed
this observation with multiple measurements in dierent wall
shades in Los Angeles in the summer of 2012 and found that
horizontal wall PFs were always less than 7 (corresponding to
dr > 0.3 as shown in Fig. 6).
PF values for skin facing the walls were simulated with the
same four scenarios (Table 2): wall albedo at 0.03 or 0.12 and
dr at 0.3 or 0.5. In these cases, we set H
b
/Dto 1 and ground
albedo to 0.12 and increased the sizes of the wall in both
Hand Wdimensions. The model predicts good protection for
sides facing the wall, provided that the size of the wall oers
sucient coverage. However, we need to remember that the
wall doesntoer any protection to the vertical side that is
facing outside and that is fully exposed.
Measurement of the umbrella SPF and comparison with
modeling
Fig. 5a and b show the diurnal variations of the measured
umbrella SPF on May 2931 2012. The PF values based on the
sky view model are included in the figures as well. The eec-
tiveness of the umbrella was greatest at mid-day (11 AM to 2
PM), when the direct sun was the strongest. The umbrella was
less eective during the morning or the afternoon when dr
was relatively high. The SPF for horizontal orientation under-
neath the umbrella varied from 2 to 6 for normal coverage (R/
H= 1) and from 7 to 16 for excellent coverage (R/H=2)
throughout the day, whereas the SPF for vertical orientation
varied from 2 to 6 for normal coverage (R/H= 1) and from 2 to
9 for excellent coverage (R/H= 2). There is overall agreement
between the measured umbrella SPF and the model-predicted
PF for both horizontal and vertical orientations (Fig. 5c). The
discrepancy seems to occur mostly in the late afternoon (e.g. at
5 PM), when the measurements conducted under the umbrella
may include some direct solar light.
Experimentally measured diuseUVtototalUVirradianceratios
Fig. 6 shows the experimentally determined erythemal diuse
UV to total UV irradiance ratios (erythemal dr) at dierent
times of the day on June 21, 2012 at Los Angeles. The ratios
determined by applying either I
horizontal
or I
vertical
for the same
time of the day (eqn (11)) were overall consistent with each
other, although the ratios determined with vertical data were
slightly higher than the ratios determined with horizontal data,
especially for the morning and late afternoon. This was probably
because the diuse UV radiation was not completely isotropic at
these time points (caused by obstructions, i.e. buildings sur-
rounding the parking lots).
Fig. 7a and b show the corresponding horizontal and vertical
SPF values determined by the actual measurement of UV inten-
sities and by applying the sky view model with the measured
erythemal dr values throughout the day of June 21, 2012. The
Fig. 3 Protection factor as a function of umbrella coverage (R/H)atdierent orientations and diuse UV to total UV irradiance ratios (dr) on
grounds of dierent reectivities (albedo) based on the sky view model (assuming zero transmission for the umbrella). (a) Top left; (b) top right; (c)
bottom left; (d) bottom right.
Photochemical & Photobiological Sciences Paper
This journal is © The Royal Society of Chemistry and Owner Societies 2017 Photochem. Photobiol. Sci.,2017,16,15371545 | 1541
Fig. 4 Horizontal umbrella view factor (UVF) and the horizontal protec-
tion factor (PF) decrease when skin under the umbrella is o-center. For
calculation of PFs, dr is set as 0.5. Xaxis represents the distance away
from the central position under the umbrella.
Table 1 Horizontal PF for walls under four scenarios: wall albedo =
0.03 or 0.12 and dr = 0.3 or 0.5. The range of the height to distance
(H/D) and the range of the width to distance (W/D) represent a variety of
wall sizes
dr = 0.3 dr = 0.5
Wall albedo = 0.03
W/Dratio W/Dratio
H/D
ratio 0.1 1 5 10 25
H/D
ratio 0.1 1 5 10 25
0.1 3.3 3.3 3.3 3.3 3.3 0.1 2.0 2.0 2.0 2.0 2.0
1 3.4 3.6 3.9 3.9 3.9 1 2.0 2.1 2.3 2.3 2.3
5 3.4 3.9 5.0 5.4 5.5 5 2.0 2.3 3.0 3.2 3.3
10 3.4 3.9 5.2 5.6 5.9 10 2.0 2.3 3.1 3.4 3.5
25 3.4 3.9 5.3 5.8 6.1 25 2.0 2.3 3.2 3.5 3.7
Wall albedo = 0.12
W/Dratio W/Dratio
H/D
ratio 0.1 1 5 10 25
H/D
ratio 0.1 1 5 10 25
0.1 3.3 3.3 3.3 3.3 3.3 0.1 2.0 2.0 2.0 2.0 2.0
1 3.4 3.6 3.8 3.8 3.8 1 2.0 2.1 2.3 2.3 2.3
5 3.4 3.8 4.8 5.1 5.1 5 2.0 2.3 2.9 3.0 3.1
10 3.4 3.8 5.0 5.3 5.5 10 2.0 2.3 3.0 3.2 3.3
25 3.4 3.8 5.0 5.4 5.7 25 2.0 2.3 3.0 3.2 3.4
Table 2 Vertical PF for positions facing the walls under four scenarios: wall albedo = 0.03 or 0.12 and dr = 0.3 or 0.5. The range of the height to
distance (H
a
/D) and the range of the width to distance (W/D) represent a variety of wall sizes. The ground albedo was set as 0.12 while the H
b
/Dwas
set as 1
dr = 0.3 dr = 0.5
W/Dratio W/Dratio
Wall albedo = 0.03
H
a
/Dratio 0.1 1 5 10 25 H
a
/Dratio 0.1 1 5 10 25
0.1 3.4 3.6 3.9 3.9 3.9 0.1 2.0 2.2 2.3 2.3 2.3
1 3.5 5.1 9.5 10.0 10.1 1 2.1 3.0 5.7 6.0 6.0
5 3.5 5.7 22.6 31.8 35.2 5 2.1 3.4 13.6 19.1 21.1
10 3.5 5.7 23.5 34.8 40.2 10 2.1 3.4 14.1 20.9 24.1
25 3.5 5.7 23.7 35.3 41.6 25 2.1 3.4 14.2 21.2 25.0
dr = 0.3 dr = 0.5
W/Dratio W/Dratio
Wall albedo = 0.12
H
a
/Dratio 0.1 1 5 10 25 H
a
/Dratio 0.1 1 5 10 25
0.1 3.3 3.5 3.6 3.6 3.6 0.1 2.0 2.1 2.2 2.2 2.2
1 3.4 4.7 7.2 7.5 7.5 1 2.1 2.8 4.3 4.5 4.5
5 3.5 5.1 12.1 13.9 14.5 5 2.1 3.1 7.2 8.4 8.7
10 3.5 5.1 12.3 14.4 15.2 10 2.1 3.1 7.4 8.7 9.1
25 3.5 5.1 12.3 14.5 15.4 25 2.1 3.1 7.4 8.7 9.2
Paper Photochemical & Photobiological Sciences
1542 |Photochem. Photobiol. Sci.,2017,16, 15371545 This journal is © The Royal Society of Chemistry and Owner Societies 2017
validity of the modeling approach for estimating the SPF of the
umbrella was confirmed by the excellent consistency (R
2
=0.97,
Fig. 7c) between the measured and model-predicted values.
Discussion
Outdoor activities are essential parts of a healthy lifestyle, but
appropriate sun protection measures should be employed to
reduce the risk of skin cancer and premature skin aging
caused by harmful UV. Seeking shade and applying sunscreens
are the two most widely used measures for sun protection.
15
Fig. 5 Horizontal SPF (a) and vertical SPF (b) as functions of the time of
the day for two coverage scenarios (R/H= 1 and R/H= 2) for May 2012,
Los Angeles. Both measured SPF values and estimated values based on
modeling are presented. There is good agreement between the model
prediction and experimental results (c).
Fig. 7 Horizontal SPF (a) and vertical SPF (b) at dierent times of the
day on June 21, 2012 in Los Angeles. Two umbrella coverage scenarios
(R/H= 1 and R/H= 2) are included for experiments and modeling.
Measured erythemal dr ratios in Fig. 6 were applied for modeling the
SPF values. There is good agreement between the model prediction and
experimental results (c, R
2
= 0.97).
Fig. 6 Experimentally determined erythemally weighted diuse UV to
total UV irradiance ratios (erythemal dr) at dierent times of the day on
June 21, 2012 in a parking lot close to the Los Angeles International Airport.
Photochemical & Photobiological Sciences Paper
This journal is © The Royal Society of Chemistry and Owner Societies 2017 Photochem. Photobiol. Sci.,2017,16, 15371545 | 1543
Several measurements of various shade devices have shown
that the protection factor of shade is generally low.
8,10,11
A side-by-side clinical study demonstrated that a beach
umbrella oered very poor sunburn protection under actual
use conditions and was less eective than a high SPF sun-
screen for an extended outdoor stay.
16
There are multiple factors that may impact a shades actual
protection level: (a) the UV absorption/reflecting properties of
the shade material and the coverage size of the shade (physical
factor of the shade); (b) the percentage of the diuse UV to
total UV irradiance ratio which may depend on the solar
zenith angle, wavelength and cloudiness etc., and UV albedo of
the ground and/or wall surface since the eectiveness of the
shade changes with the environment (environmental factor);
and (c) the position and orientation under the shade (human
behavior factor). This study is among the first to systematically
investigate the impact of all these factors. We found that the
PF of an umbrella decreases with the UV transmission of the
umbrella materials and SVF (i.e. higher SVF means less cover-
age). PF also decreases with greater dr ( for both horizontal and
vertical orientations). The model not only allows us to under-
stand the range of protection levels a typical shade structure
may provide, but also allows us to estimate the optimal PF that
a shade device can achieve. For an umbrella exhibiting zero UV
transmission located on a non-reflecting ground surface, the
optimal PF is determined mainly by the SVF and dr:
Optimal PF of umbrella ¼1=ðSVF drÞ
Shade is most eective when dr is the lowest (0.3 in Fig. 6),
so for typical coverage (R/H=1orapproximately4050% cover-
age) the optimal PF can be 78, and for excellent coverage
(R/H=2orapproximately7080% coverage) the optimal PF can
be 1217. The findings were experimentally confirmed by actual
measurements of UV intensities with and without the umbrella.
Under actual use conditions, umbrella PF can be much lower
than optimal due to the movement of people (Fig. 4).
The current model does not take into consideration the variation
of body shapes and curvatures, surface textures, or interactions
between dierent body parts. In addition, diuseUVirradianceis
not isotropic
17
as implied in the current model so a more accurate
calculation will need to incorporate knowledge of the angular dis-
tribution of diused UV rays. Nevertheless, our approach provides
a simple and quantitative way to help understand the protection
levels oered by umbrellas and walls as observed. It also helps to
enable the proper design, selection, and use of shade structures
for optimal sun protection. While shade remains a convenient
method for sun protection, it is not foolproof and certainly does
not oer full protection. People may still need to wear sunscreen
or protective clothing when in the shade for extended outdoor stays.
Abbreviations
PF Protection factor
tr Transmission
UVF Umbrella view factor
SVF Sky view factor
GVF Ground view factor
dr Diuse UV to total UV irradiance ratio or diuse ratio
MED Minimal erythema dose
SPF Sun protection factor
CIE International commission on illumination
Conicts of interest
The authors are employed by Johnson & Johnson Consumer Inc.
Appendix: O-center umbrella
coverage (horizontal scenario)
For applying the sky view model, we assume that the skin is
located at the center of the shade under the umbrella;
however, that is not always the case in real-life. Here we
explore how moving away from the center can impact horizon-
tal PF (Fig. 8).
The shade projection on the detector (R) is dependent on
R, which ranges from (RX)to(R+X), where Xis a variable.
R′′ ¼sin tan1R
H

Rcan be described as a function of γ(Fig. 9) because
R
sin γ¼X
sin β¼R
sin α
β¼sin1Xsin γ
R

R¼
Rsin πsin1Xsin γ
R

γ

sin γ
The UVF can be calculated by integrating the shade projec-
tion based on R.
UVF ¼1
2πð2π
γ¼0
R′′2dγ
Fig. 8 Side view of umbrella projection on the detector when it is o-
center by X.
Paper Photochemical & Photobiological Sciences
1544 |Photochem. Photobiol. Sci.,2017,16, 15371545 This journal is © The Royal Society of Chemistry and Owner Societies 2017
Fig. 10 shows an example of umbrella shade projection on the
unit detector where R/H=1,andX/R= 0.5. The shade projection
is no longer symmetrical and is closer to the umbrella edge.
References
1 A. V. Parisi and D. J. Turnbull, Shade provision for UV mini-
mization: A review, Photochem. Photobiol., 2014, 90, 479
490.
2 A. V. Parisi, M. G. Kimlin, J. C. Wong and M. Wilson,
Diuse component of the solar ultraviolet radiation in tree
shade, J. Photochem. Photobiol., B, 2000, 54, 116120.
3 M. P. Utrillas, M. J. Marin, A. R. Esteve, F. Trena, J. Canada,
V. Estelles and J. A. Martinez-Lozano, Diuse UV erythemal
radiation experimental values, J. Geogr. Res., 2007, 112,
D24207.
4 A. A. Silva, The diuse component of erythemal ultraviolet
radiation, Photochem. Photobiol. Sci., 2015, 14, 1941
1951.
5 A. F. Moise and R. Aynsley, Ambient ultraviolet radiation
levels in public shade settings, Int. J. Biometrorol., 1999, 43,
128138.
6 D. J. Tunbull, A. V. Parisi and J. Sabburg, Scattered UV
beneath public shade structures during winter, Photochem.
Photobiol., 2003, 78, 180183.
7 D. J. Turnbull and A. V. Parisi, Annual variation of the
angular distribution of the UV beneath public shade struc-
tures, J. Photochem. Photobiol., B, 2004, 76,4147.
8 P. Gies and C. Mackay, Measurement of the solar UVR
protection provided by shade structures in New Zealand
primary schools, Photochem. Photobiol., 2004, 80, 334
339.
9 A. V. Parisi, D. J. Turnbull, C. de Byl, P. Schouten, J. Turner
and N. Downs, Influence of cloud and solar zenith angle
on the diuse solar erythemal UV short wavelength cut-os
and maximum spectral irradiance wavelengths, Radiat.
Prot. Aust., 2009, 26,29.
10 D. J. Turnbull and A. V. Parisi, Increasing the ultraviolet
protection provided by shade structures, J. Photochem.
Photobiol., B, 2005, 78,6167.
11 D. J. Turnbull and A. V. Parisi, Eective shade structures,
Med. J. Aust., 2006, 184,1315.
12 M. P. Utrillas, J. A. Martinez-Lozano and M. Nunez,
Ultraviolet radiation protection by a beach umbrella,
Photochem. Photobiol., 2010, 86, 449456.
13 A. I. Kudish, M. Harari and E. G. Evseev, The solar UVB
radiation protection provided by shading devices with
regard to its diuse component, Photodermatol.,
Photoimmunol. Photomed., 2011, 27, 236244.
14 M. de Paula Correa and J. C. Ceballa, UVB surface albedo
measurement using biometers, Rev. Bras. Geofis., 2008, 26,
411416.
15 J. K. Robinson, D. S. Rigel and R. A. Amonette,
Summertime sun protection used by adults and their
children, J. Am. Acad. Dermatol., 2000, 42(5Pt1), 746
753.
16 H. Ou-Yang, L. Jiang, K. Meyer, S. Q. Wang, A. S. Farberg
and D. S. Rigel, Sun protection by beach umbrella vs. high
SPF sunscreen, JAMA Dermatol., 2017, 153(3), 304308.
17 C. Kuchinke and M. Nunez, An anisotropy correction
method for all-sky measurement of diuse UV-B erythemal
irradiance, J. Atmos. Oceanic Technol., 2003, 20, 1523
1533.
Fig. 9 Top view of the umbrella with radius, R, with the detector
beneath it with a distance, X, from the center.
Fig. 10 Example of UVF projection on the detector (R/H= 1 and X/R=
50%).
Photochemical & Photobiological Sciences Paper
This journal is © The Royal Society of Chemistry and Owner Societies 2017 Photochem. Photobiol. Sci.,2017,16, 15371545 | 1545
... There are few clinical outdoor studies that specifically evaluate the UV protectiveness of shade. In a recent study, Ou-Yang et al. showed that shade from a beach umbrella provided less effective sun protection than did a high-SPF sunscreen [233,234]. Shade, recommended by many groups for the prevention of skin cancer, is effective in reducing the amount of exposure to UV rays in general, but the magnitude of reduction and clinical effectiveness may be less than expected. Tizek et al. compared the unique sun exposure patterns and sun protection behavior of foresters with those of other outdoor workers and their relation to the keratinocyte carcinoma risk. ...
Chapter
Full-text available
Since time immemorial, people protected themselves from solar radiation. Limiting time in the sun by seeking shade or wearing clothing was a matter of course. In the early 20th century, tanned skin - a result of exposure to sunlight - was associated with good health. At the same time, however, one also had to protect oneself against the potential of excessive exposure to avoid sunburns. Around 1945, the first sunscreen products for protection against solar radiation became available. In the years to follow and up to the recent past, a vast number of different sunscreen filters were developed and incorporated into a wide variety of product formats. Frameworks regulating filter substances and preparations and methods to characterize sunscreen products' performance parameters were developed. Over the past 50-70 years, the perception regarding the tasks of sunscreen products changed several times. It was initially promoted as a lifestyle product and had the task of preventing sun-related erythema (tan without burn). Later, the prevention of skin cancer was added. Only in recent times, sunscreen products have been increasingly advertised and perceived as beauty and lifestyle products again. Also, the use of sunscreen products for antiaging purposes is now commonplace. The different intended purposes (averting harm and prevention) and the widespread use of topical sunscreen products have promoted many investigations and generated a vast and ongoing need for consumer and patient information and education. In the following review, we analyze and discuss current topics from conflicting areas, such as sun protection products (e.g., ideal sun protection products, sun protection metrics), product safety (e.g., nanoparticulate sunscreen filters, regulatory issues), application in everyday life (e.g., wish to tan, vulnerable cohorts), as well as controversies and future challenges (e.g., risks and benefits of UV radiation).
... In all skin cancers, exposure to ultraviolet radiation (UVR) is the main environmental risk factor and an initiator of carcinogenic mutations [5][6][7][8]. Thus, skin cancer is often referred to as highly preventable, as primary preventive measures can be directed at promoting accurate sun protection to individuals, or groups of individuals, with the highest risk due to phenotypic, environmental, and behavioural factors [9][10][11][12][13][14][15][16][17]. In order to be able to do so, there is a need for valid and reliable tools to measure sun exposure habits and sun protection behaviour, both in order to identify individuals with a risky behaviour with regard to skin cancer, as well as to be able to communicate individually tailored sun protection advice [18][19][20]. ...
Article
Full-text available
The Sun Exposure and Protection Index (SEPI) is a brief instrument for scoring of sun exposure habits and propensity to increase sun protection, previously validated in English and in Swedish, as well as in two different outdoor sun intensity environments (Australia and Northern Europe). The aim of the present study was to study reliability and validity of a German translated version of the SEPI to be used in German-speaking populations. Data was collected at University of Flensburg and at Hamburg University of Applied Sciences from November 2018 to April 2019. Participants (n = 205) filled out the SEPI and also a selection of corresponding questions from the Austrian Vienna UV Questionnaire in German. After three weeks, the participants filled out the SEPI once again in order to assess test–retest stability. Of the 205 participants completing the baseline questionnaire, 135 participants completed it once again after three weeks. Internal consistency, by Cronbach’s alpha, for the baseline responses was 0.70 (95% C.I: 0.63–0.76) for SEPI part 1 (sun exposure habits) and 0.72 (95% C.I: 0.66–0.78) for part 2 (propensity to increase sun protection). Test–retest stability was high, with weighted Kappa >0.6 for all items but one, and the instrument correlated well with the previously validated German-language UV Skin Risk Survey Questionnaire. In conclusion, the German version of SEPI can reliably be used for mapping of individual sun exposure patterns.
... Integration of nanostructured biocompatible organic and inorganic materials on the flexible substrates such as textiles, paper, kapton, aluminum foil and plastics has strong emphasis on the design of multifunctional materials for applications like self-cleaning (Qi and Xin, 2010), antimicrobial activity (El-Molla et al., 2011;Wang et al., 2016), durability (Ibrahim et al., 2015), flame retardancy (El-Hady et al., 2013), water repellency (Xue et al., 2008), wearable electronic applications (Athauda et al., 2013), wearable, bio sensor (Magenes et al., 2011) and flexible gas sensor , thermochromic sensor (Gao et al., 2017), electrochromic sensor (Molina, 2016) and coloration (Athauda et al., 2013;Emam and Abdelhameed, 2017). The surface modified textiles have been suggested by dermatologists and cancer society (Gordon, 2009) for protecting people from UV radiation (280e400 nm) (Xiao et al., 2015), which can cause several skin diseases like sunburn, tanning, eye damage, skin cancer, premature aging of the skin, suppression of the immune system (Kullavanijaya and Lim, 2005;Osterwalder and Herzog, 2010;Ou-Yang and Shyr, 2017). ...
Article
The surge in skin cancer cases across the globe has forced the scientific community to develop solutions to protect humans against the ill effects of ultraviolet (UV) radiation. Nowadays, functionalized cotton textiles are employed to protect humans against UV radiation. In this context, nanostructured ZnO modified cotton fabrics towards the enhancement of ultraviolet protection factor (UPF) as well as to develop wearable gas sensors have been developed. The surface of carbon cellulosic fabric was modified by sol-gel and sputter seed layer-coated sol-gel techniques. ZnO grown fabrics were characterized using X-ray Diffractometer (XRD), Field Emission Scanning Electron Microscope (FE-SEM), Thermogravimetric Analysis (TGA), X-ray Photoelectron Spectrometer (XPS) and Fourier Transform Infrared Spectrometer (FTIR). Subsequently, UV-blocking and gas sensing properties of the modified textile samples were investigated. The seed layer initiated sol-gel modified cotton fabric showed a maximum UV protection factor (UPF) of 378. Also, room temperature gas-sensing performance of the functionalized cotton fabric towards volatile organic compounds such as acetaldehyde, ammonia and ethanol vapours was investigated.
Article
Full-text available
Importance: Sun-protective behavior affects skin cancer prevention. Shade works by physically shielding skin from direct harmful UV rays; however, skin may still remain exposed to reflected and indirect UV rays. There is no current standard metric to evaluate shade for its effectiveness in sun protection, and there is insufficient clinical evidence that a beach umbrella alone can provide adequate sun protection. Objective: To directly measure sunburn protection offered by a standard beach umbrella compared with that provided by sunscreen with a high sun protection factor under actual use conditions. Design, setting, and participants: A single-center, evaluator-blinded, randomized clinical study was conducted from August 13 to 15, 2014, in Lake Lewisville, Texas (elevation, 159 m above sea level), among 81 participants with Fitzpatrick skin types I (n = 1), II (n = 42), and III (n = 38). Participants were randomly assigned to 2 groups: 1 using only a beach umbrella, and the other using only sunscreen with a sun protection factor of 100. All participants remained at a sunny beach for 3½ hours at midday. Clinical sunburn evaluation of each individual for all exposed body sites was conducted 22 to 24 hours after sun exposure. Interventions: The shade provided by a beach umbrella or protection provided by sunscreen with a sun protection factor of 100. Main outcomes and measures: Sunburn on all exposed body sites 22 to 24 hours after sun exposure. Results: Among the 81 participants (25 male and 56 female; mean [SD] age, 41 [16] years) for all body sites evaluated (face, back of neck, upper chest, arms, and legs), the umbrella group showed a statistically significant increase in clinical sunburn scores compared with baseline and had higher postexposure global scores than the sunscreen group (0.75 vs 0.05; P < .001). There was a total of 142 sunburn incidences in the umbrella group vs 17 in the sunscreen group. Thirty-two of the 41 participants (78%) in the umbrella group showed erythema in 1 or more sites vs 10 of the 40 participants (25%) in the sunscreen group (P < .001). Neither umbrella nor sunscreen alone completely prevented sunburn. Conclusions and relevance: A beach umbrella alone may not provide sufficient protection for extended UV exposure. It is important to educate the public that combining multiple sun protection measures may be needed to achieve optimal protection. Trial registration: isrctn.org Identifier: ISRCTN19177299.
Article
Full-text available
Occulting disk or shadowband arrangements are often applied to both spectral and broadband sensors in order to retrieve the total diffuse irradiance. However, there is difficulty in the application of a suitable diffuse correction due to the instrument cosine response. Generally, the sky radiance distribution is assumed isotropic during the correction, although it has been shown in most studies to be nearly always anisotropic. This study presents a method for using a measurement of the actual anisotropy of the UV-B sky in order to derive correction factors to account for the integral of this anisotropy and the nonideal cosine functions in the response of instruments; the method being applicable when the instruments carry out synchronous spectral or broadband measurements. In situ erythemal sky radiance distribution data are obtained from a variable sky-view platform (VSP). The VSP consists of a Solar Light Company 501-A UV biometer that moves up and down within a vertically aligned fixed shading cylinder, therefore causing the sky-view factor to vary in discrete steps. VSP output is used to correct for the cosine error of instruments that measure diffuse erythemal radiation data (less than 400 nm), for both clear-sky and cloudy conditions. Results show that an isotropic diffuse correction overestimates the real diffuse signal by a maximum of 4%-6% for clear skies, with this magnitude decreasing with an increase in solar zenith angle (SZA). This is in accordance with the increase in sky isotropy at large SZAs. In contrast, the overestimate at small to mid-SZAs for stratocumulus and cumulus cloud conditions ranges from approximately 2%-5% for moderate cloud cover to 0%-10% for high cloud cover. Here, the overestimate variability can be significant at large SZAs. Results under cloudy skies are affected by both variability in cloud sky distribution and VSP signal error resulting from loss of sensitivity. Overall, it is expected that cloud distribution masks the effect of increased sky isotropy.
Article
Full-text available
Measurements of diffuse UV erythemal radiation (UVER) using a shadowband have been corrected using the models proposed by Drummond (1956), LeBaron et al. (1990), and Batlles et al. (1995). Two different methods were used to validate these models: intercomparison with an Optronic OL754 spectroradiometer and comparison with the values simulated by two radiative transfer codes, SMARTS and SBDART. For this comparison only clear days have been used. The corrected experimental values were analyzed in order to study the average values of the diffuse UVER fraction in relation to the clearness index kt. These varied between 62%, for kt close to 0.8, and 93% for kt of 0.2-0.3. Finally, a study of the monthly average and extreme values of the UV Index for diffuse radiation is presented, showing a maximum value of 6 in June.
Article
Full-text available
This work describes ultraviolet-B albedo measurements performed over several surfaces and different atmospheric conditions. These results provide a complement to previous studies as Blumthaler & Ambach (1988), widely used as albedo reference for the main UV radiative transfer models. A custom-built albedometer composed of a pair of Solarlight UVB501 biometer was used to measure the albedo over the following surfaces: green and yellowish grass, sand, wood (natural and painted), formica (synthetic plate), and iron. Influence of clouds and the sensor's response to temperature variations are also discussed. Presence of clouds on surface albedo measurement seems negligible, but a thermo-regulated instrument is indispensable to an accurate analysis. Comparison with previous works shows the need for studies on the detailed characterization of the type of surface.
Article
The diffuse (Dif) component of ultraviolet radiation (UVR) plays an important role in the daily exposure of humans to solar radiation. This study proposes a semi-empirical method to obtain the Dif component of the erythemal dose rate, or the erythemally weighted irradiance, (EDRDif) calculated from synchronized measurements of the Dif component of UVR (UVDif) and the global (G) irradiances of both UVR (UVG) and the erythemal dose rate (EDRG). Since the study was conducted in the tropics, results involve a wide range of solar zenith angles to which EDRDif is seasonally dependent. Clouds are the main atmospheric agent affecting Dif radiation. The ratio between Dif and G (Dif/G) showed a quadratic dependence on cloud cover with a coefficient of determination r(2) = 0.79. The maxima of EDRDif were mainly above the moderate range (>137.5 mW m(-2)) of the UV-Index and reached the extreme range (>262.5 mW m(-2)) for the spring-summer period. The fraction of the global daily erythemal dose (daily EDG) corresponding to Dif radiation (daily EDDif) ranged from 936 J m(-2) to 5053 J m(-2) and averaged 2673 J m(-2). Daily EDDif corresponded to at least 48% of daily EDG for a practically cloudless sky. Therefore, Dif radiation is a real threat. Lighter skin people (types I and II) can get sunburnt in a couple of minutes under such an incidence of radiation. Moreover, accumulative harm can affect all skin types.
Article
Minimising exposure to ultraviolet (UV) radiation is an essential component of skin cancer prevention. Providing and using natural and built shade is an effective protection measure against harmful UV. This article describes the factors that must be addressed to ensure quality, effective, well designed shade and recommends best practice approaches to improving the protection factor (PF) of shade structures. It identifies examples of interventions to increase shade availability and use, and examples of effective shade based on measured protection factors or measured reductions in UV exposures. Finally, this article considers examples of best practice for undertaking shade audits. The article is based on refereed papers and reviews, reports, conference papers, and shade practice and policies from reports and on web sites. Articles for the Australian setting are considered first, followed by those in an international setting. This article is protected by copyright. All rights reserved.
Article
Broadband field measurements were conducted beneath three different-sized public shade structures, small, medium and large, during winter in the Southern Hemisphere. These measurements were compared with the diffuse UV to quantify the relationship of the UV under and around the shade structures to the diffuse UV. For the shade structures, a relationship between the diffuse UV and the UV in the shade has been provided for clear skies and solar zenith angles (SZA) of 49–76°. This allows the prediction of the UV in the shade of these structures if the diffuse UV is known. The ultraviolet protection factors for the three shade structures ranged from 1.5 to 5.4 for decreasing SZA. For the greater SZA of 70–76°, the erythemal UV in the shade was 65%, 59% and 51% of that in full sun for the small, medium and large structures, respectively. For the smaller SZA of 50–53° the erythemal UV in the shade was 35%, 41% and 18% for the small, medium and large shade structures, respectively. From this research it can be concluded that the UV radiation levels in the shade in winter could cause erythema and other sun-related disorders.
Article
Background: The composition of the incident solar global ultraviolet B (UVB) radiation with regard to its beam and diffuse radiation fractions is highly relevant with regard to outdoor sun protection. This is especially true with respect to sun protection during leisure-time outdoor sun exposure at the shore and pools, where people tend to escape the sun under shade trees or different types of shading devices, e.g., umbrellas, overhangs, etc., believing they offer protection from the erythemal solar radiation. The degree of sun protection offered by such devices is directly related to the composition of the solar global UVB radiation, i.e., its beam and diffuse fractions. Methods: The composition of the incident solar global UVB radiation can be determined by measuring the global UVB (using Solar Light Co. Inc., Model 501A UV-Biometer) and either of its components. The beam component of the UVB radiation was determined by measuring the normal incidence beam radiation using a prototype, tracking instrument consisting of a Solar Light Co. Inc. Model 501A UV-Biometer mounted on an Eppley Solar Tracker Model St-1. The horizontal beam component of the global UVB radiation was calculated from the measured normal incidence using a simple geometric correlation and the diffuse component is determined as the difference between global and horizontal beam radiations. Results: Horizontal and vertical surfaces positioned under a horizontal overhang/sunshade or an umbrella are not fully protected from exposure to solar global UVB radiation. They can receive a significant fraction of the UVB radiation, depending on their location beneath the shading device, the umbrella radius and the albedo (reflectance) of the surrounding ground surface in the case of a vertical surface. Conclusions: Shading devices such as an umbrella or horizontal overhang/shade provide relief from the solar global radiation and do block the solar global UVB radiation to some extent; nevertheless, a significant fraction of the solar global UVB radiation does penetrate this supposedly 'protective or comfort zone'. As a result, it is imperative to either apply sunscreen or cover up the exposed body surfaces even when under such shading devices.
Article
A beach umbrella intercepts all direct UV irradiance, but only part of the diffuse component. Using a simple sky view factor model, we have determined the fraction of the hemispheric diffuse irradiance that is not intercepted by the umbrella. Assuming a sensor at the surface and close to the center of the umbrella, isotropic diffuse irradiance and for an umbrella of 80 cm radius and 100 cm high, our results show that approximately 34% of the incident horizontal irradiance is not intercepted by the umbrella. These results agree with irradiance measurements conducted with and without the umbrella. The model is next extended to examine receipt of UV radiation by a human figure in a vertical position, either standing or sitting.