Spectral sensitivity of the human eye

Spectral sensitivity is the relative efficiency of detection of light or other signal, as a function of the frequency or wavelength of the signal.

There are two basic types of retinal photo-receptors

Cones cell -> responding to bright-light condition (Photopic vision).
Rod cell -> responding to low-intensity light condition (Scotopic vision).

Depending on their spectral sensitivity, belong to either

Long-wavelengths sensitive (L)
Mid-wavelengths sensitive (M)
Short-wavelengths sensitive (S)

By combining their inputs, the brain can create colors. Mostly, the cones are concentrated in the center of the retina (Fovea).

Eye spectral sensitivity is influenced by light intensity to which is exposed. Light intensity determines the level of activity of cones & rods. And the light intensity also determines main characteristic of human vision.

Visible spectrum, what is sensitivity of cones & rods varies with the wavelength, ranging from 370 nm to 730 nm. Energy level equivalent the wavelength of light wave stimulates eye photo-receptors, which send received stimulus to the brain. This can be produce an input from which the brain create perception of color.

Sensitivity of human eyes to light increase exponentially with the decrease in light intensity. In day-light condition, the wavelength of peak sensitivity is 550 nm. And then, in darkness, the wavelength of peak sensitivity is 507 nm. So, as light intensity decreases, cone function changes more effective light collection.

Whereas, decreasing light intensity stimulates accumulation of rhodopsin in rods. Rhodopsin is washed out at higher light intensity. In activates rods, enabling the eye to respond to light stimuli of much lower intensity.

Sources : Gigahertz-Optic : http://www.light-measurement.com/spectral-sensitivity-of-eye/ Wikipedia : http://en.wikipedia.org/wiki/Spectral_sensitivity Naver : http://endic.naver.com/enkrEntry.nhn?entryId=59b4cdfcbb25434ba38c5c79f0d3c82f Naver : http://terms.naver.com/search.nhn?query=spectral+sensitivity&where=&x=0&y=0