Sensitivity of the Human Eye (2024)

Abstract

DR. SELIG HECHT, professor of biophysics at Columbia University, has recently made a tour of American colleges and universities, during which he has lectured to fifteen different Chapters of the Society of the Sigma Xi. His lecture gave some interesting data, arising from his own researches, on the sensitivity of the eye. Under the most favourable conditions, the smallest amount of light which the human eye can detect is 58–148 quanta, representing an energy of 2–6 × 10^-10 ergs. This 58–148 quanta is the amount of light falling on the cornea, but only about 10 per cent (5–14 quanta) of this is actually absorbed by the retina; the rest is lost by corneal reflexion (4 per cent), absorption by ocular media (50 per cent) and passing on beyond the retina (36 per cent). In the particular experiments described, this 5–14 quanta were absorbed by an area of retina which contained about five hundred receptor cells (rods). It seems reasonable to suppose, therefore, that each quantum was absorbed by a separate receptor cell. Chemical studies have shown that one quantum of light changes (bleaches) one molecule of visual purple. The conclusion reached is that we can see a light when the energy from it is sufficient to bleach one molecule of visual purple in each of 5–14 separate receptor cells.

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