American Board of Opticianry (ABO) Practice Test

Which wavelengths of light activate photochromatic lenses?

1. The muscle that moves the eye inward

2. The red numbers on a lens clock

3. Differing refractive errors for the two eyes

4. Ultraviolet radiation

The correct answer is: Ultraviolet radiation

Photochromatic lenses are lenses that automatically darken in bright lights and clear up in normal or dim light. The lenses work by responding to UV light, causing a chemical reaction that darkens the lenses. This is why only ultraviolet (UV) radiation is able to activate photochromatic lenses. Option A is incorrect because it refers to the muscles that move the eye inward, which has nothing to do with the activation of photochromatic lenses. Option B is incorrect because it refers to the red numbers on a lens clock, which are used for adjusting the lenses and have no effect on their activation. Option C is incorrect because it refers to differing refractive errors for the two eyes, which is a condition that affects vision and is unrelated to the activation of photochromatic lenses.