Acuity by Night

Night driving is risky enough, warns St. Louis' Dr. Paul W. Miles in the Archives of Ophthalmology, but colored glasses or tinted windshields can make it downright dangerous. The big trouble: the loss of visual acuity because too much light is cut out.

Taking plain and colored glass in turn. Dr. Miles lists their effects. If ordinary daytime vision is 20/20, then visual acuity at night, through clear glass, is cut to 20/32. A popular "night glass" of light yellow reduces visual acuity only to 20/34. But Dr. Miles found that a second popular shade, pink, cut visual acuity to 20/40. Finally, a green windshield reduced nighttime acuity to 20/46, but in combination with the pink glasses, it slashed vision to a deadly 20/60.

Dr. Miles's advice: green filters for sun glare should be lifted out of the way at night, and colored glasses should be left in the glove compartment.

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