ABSTRACT
An atmospheric window for solar radiation in the 400-700 nm range makes photons of these wavelengths plentiful on Earth. Reflected and scattered in varying degrees from everything in the environment, a directional response to impinging photons can provide information about those things from a distance. Fortunately, such photons have sufficiently low energy to penetrate organic tissue without damage, yet have sufficiently short vibrations to make detailed images possible in optical systems scaled to the dimensions possible with animal cells. Small wonder that most animals have evolved some capacity for directional detection of photons in this wavelength range, which we call light. Ergonomists measure light because humans receive about 90% of their information from the environment by processing visual responses to light.
