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A whitened shirt looks dramatically brighter outdoors than under a shop lamp chiefly because

  • A.the whitener degrades under the heat of the artificial lamp itself
  • B.daylight contains far more ultraviolet radiation than the lamp does
  • C.the illuminance out of doors is very much higher than it is indoors
  • D.the observer adapts differently to daylight than to artificial light

Answer: B

Fluorescent emission is proportional to the ultraviolet energy absorbed. Daylight is rich in ultraviolet whereas most incandescent and many fluorescent lamps carry very little, so the whitener contributes far less indoors.

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