shifts to a higher luminance when: The
peripheral luminance (luminance of the lamp
excluding the LEDs) approaches the lumi-
nance of the LED luminaire and the number
of LEDs increases in a fixed area.
Furthermore, they concluded that the BCD
shifts to lower luminance when: The lamp size
increases, but keeping the same number of
LEDs and the lamp size increases, but keep-
ing the separation constant. In addition, Lee
et al.
15
studied uniform fluorescent tubes
and LED modules at 20 8 vertically. The
LEDs were circular. The results showed
that non-uniform LED modules lead to
more glare perception. Moreover, contrary
to Kasahara’s conclusion, discomfort glare
increases when the distance between neigh-
bouring LEDs decreases. Additionally,
Hibino et al.
16
studied visual stress caused
by LEDs with different geometric patterns,
such as matrix, stripe and checker at the line
of sight. It revealed that matrix arrangement
leads to significant higher discomfort than
checker arrangement when keeping the same
interval, 5 mm.
Finally, Tashiro et al.
17
tried to modify
UGR to apply it to non-uniform LED
luminaires. They investigated LED discom-
fort glare with many types of distributions at
8.5 8 above the line of sight. They included a
raw LED matrix, a LED with a lens and a
LED with a diffuser. They revealed that non-
uniform glare sources produce more discom-
fort glare than uniform ones when keeping
L
ave
of the glare sources the same.
Furthermore, they proposed a term ‘effective
glare luminance’ (L
eff
) to replace L
ave
. The
less uniform the glare source, the higher L
eff
will be, even keeping the L
ave
of glare source
the same. After replacing L
ave
with L
eff
to
modify the UGR, there has been a large
improvement in the fit to the data.
Although previous studies have demon-
strated that non-uniform LED luminaires
lead to more discomfort glare than uniform
conventional light sources, there is a need to
conduct a comprehensive study between vari-
ous luminance distributions of LED lumin-
aires under different background lighting
conditions and positions of glare sources.
The aims of this study are:
To compare the discomfort glare caused by
different types of LED luminaires of typical
luminance distribution.
To test UGR’s performance in predicting
discomfort glare caused by them, and
To produce a comprehensive database for
the modification of UGR or for developing
a new glare model.
This paper is the first part of a series. The
work is distributed according to the above
three goals.
2. Experiment
2.1 Experimental conditions
Figure 2 shows the experimental setup in
an office-like room. The LED panel was hung
on a white wall and the wall was 2.5 m in
front of observer’s eyes. There were two kinds
of orientation angles of the LED panel, 10 8
and 20 8 above the line of sight for a 1.7 m
observer sitting on a chair. This was easily
realised by adjusting the height of the LED
panel. There were two different background
luminances, bright and dark. They were
realised by turning on and off the fluorescent
tubes on the ceiling, these tubes having a
correlated colour temperature (CCT) of
5500 K.
The observers were asked to look at a
display showing neutral grey and images of
the paintings of Monet. The distance between
observer and display was 60 cm. The centre of
the display had the same height as the
observer’s eyes. The display was set to a
white point of about 6500 K at 100 cd/m
2
measured under dark ambient. It was
1.2 cd/m
2
brighter under bright ambient.
These luminances were measured by a
JETI
Õ
Specbos 1211 UV spectroradiometer.
4 Y Yang et al.
Lighting Res. Technol. 2015; 0: 1–16
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