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Unformatted text preview: Brightness Comparison In the laboratory, the output of two lasers are viewed (with the eye) under iden-
tical conditions. The laser beams are incident on a diffusing screen. The ﬁrst laser is a
10 mW helium-cadmium of freespace wavelength 441.6 nm. The second laser is 1.5 mW
helium-neon laser of freespace wavelength 632.8 nm. All conditions are identical except
for the wavelengths and radiant powers. Calculate, showing all work, the luminous power for each laser. Express the lu-
minous power in lumens accuartely to three signiﬁcant ﬁgures. State which laser would
appear brighter. Helium-cadmium laser luminous power = lumens.
Helium-neon laser luminous power = lumens. The brighter laser is Brightness Comparison Helium-cadmium laser
A = 441.6 nm
Luminous Efficacy = 0.023 + (0.16)(0.038 — 0.023) = 0.0254 Luminous Power = (Radiant P0wer)(680lumens/watt)(0.0254) = 0.173lumens Helium—neon laser
A = 632.8 nm
Luminous Efficacy = 0.265 + (0.28)(0.265 — 0.175) = 0.2398 Luminous Power = (Radiant Power)(680lumens/watt)(0.2398) = 0.245 lumens Therefore the helium-neon laser appears brighter. ...
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- Spring '08