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Unformatted text preview: Photometric Comparison of LED’s Three light-emitting diodes (LED’s) are viewed in the laboratory. The ﬁrst is a SiC
LED emitting at 480 nm (blue) and is viewed at an angle of 10° from the axis of the device
(the axis of the device being normal to the emitting surface). The second is a GaP:N LED
emitting at 565nm (yellow—green) and is viewed at an angle of 75° from the axis of the
device. The third is an AlGaP LED emitting at 620 nm (orange) and is viewed at an angle
of 20° from the axis of the device. Each of the three LED’s has a total output optical
power of 5mW emitted into a Lambertian distribution. Each of the three LED’S has an
output area of 1 mm x 1 mm. Quantitative measurements of the LED’s are made at these angles with a photodetector that has an area of 4mm2 and is positioned 100 mm from the
LED. Calculate, showing all work, the luminous intensity of each LED for the viewing
angles given. Express your answers in lumens/stemdian accurately to four signiﬁcant
ﬁgures. Which appears the brightest for these viewing angles? Which appears the least
bright for these Viewing angles? Calculate the luminance of each LED. Express your 2 answers in lumens/steradian mm accurately to four signiﬁcant ﬁgures. Put your answers in the spaces provided. Luminous intensity of the ﬁrst LED (blue) 2 lm/sr.
Luminous intensity of the second LED (yellow—green) = lm/sr.
Luminous intensity of the third LED (orange) 2 lm/sr.
Luminance of the ﬁrst LED (blue) 2 lm/sr mmz. Luminance of the second LED (yellow-green) = lm/sr mm2. Luminance of the third LED (orange) 2 lm/sr mmz. Photometric Comparison of LED’s Differential area on surface of sphere dA = (7" d0)(r sinngb) Differential solid angle d9 = d??— = 51710030qu Total power emitted by LED 7r/2 271'
0:0 ¢=0 Pt 7r/2 21r SW20
2 <15 IRO O O
= WIRO Radiant intensity at 0 : 0° P
[R0 =—. _‘
71' H 1.5915mW/s7‘ Radiant intensity at 0 IR 2 [1300080
1R1 = 1.5674mW/sr 02100 0.4119 mW/sr (9 = 750 :0“
H 1.4956 mW/sr 6 = 20° 5
n Luminous Efﬁciencies A = 480nm LE 2 0.139
/\ = 565nm LE 2 0.9735
A = 620nm LE = 0.381 Luminous intensity at 0 [Li = IRi LEz‘ “380%“ 1W
1000mW Luminance L1- = 1R0 c080 (LEi) (680%) ( é“
II 0.27268 1771/31" 9
|| 0.1504 lm/sr mm2
1.0536 lm/sr mm2 0.41234lm/s7‘ mm2 1W
1000mW 0.14515 lm/sr least bright 0.38747 lm/sr brightest )/As cos 0 ...
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- Spring '08