Spectral sensitivity of the human eye and related quantities

The sensitivity of the human eye to light of a certain intensity varies strongly over the wavelength range between 380 and 800 nm. Under daylight conditions, the average normal sighted human eye is most sensitive at a wavelength of 555 nm, resulting in the fact that green light at this wavelength produces the impression of highest “brightness” when compared to light at other wavelengths. The spectral sensitivity function of the average human eye under daylight conditions (photopic vision) is defined by the CIE spectral luminous efficiency function. Only in very rare cases, the spectral sensitivity of the human eye under dark adapted conditions (scotopic vision), defined by the spectral luminous efficiency function, becomes technically relevant. By convention, these sensitivity functions are normalized to a value of 1 in their maximum.

As an example, the photopic sensitivity of the human eye to monochromatic light at 490 nm amounts to 20% of its sensitivity at 555 nm. As a consequence, when a source of monochromatic light at 490 nm emits five times as much power (expressed in watts) than an otherwise identical source of monochromatic light at 555 nm, both sources produce the impression of same “brightness” to the human eye.

Quantities related to senstivity of human eye

Units like Lumens (lm) take into account eye perception while radiometric units like Watts (W) only take into account physical aspects.

Luminous flux (lm): energy per unit time over visible region-weighted average of radiant flux for eye sensitivity. At 555 nm, radiant power of 1 W corresponds to 683 lm (photopic version).

Luminous intensity (lm sr-1, cd): 1 lm = 1/4π cd.

Luminous efficacy (lm W-1): a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt.

人眼敏感度曲线（txt数据 第一列为明视觉，第二列为暗视觉）

380    2E-4        5.89E-4
390    8E-4        0.00221
400    0.0028     0.00929
410    0.0074     0.03484
420    0.0175     0.0966
430    0.0273     0.1998
440    0.0379     0.3281
450    0.0468     0.455
460    0.06         0.567
470    0.091       0.676
480    0.139       0.793
490    0.208       0.904
500    0.323       0.982
510    0.503       0.997
520    0.71         0.935
530    0.862       0.811
540    0.954       0.65
550    0.995       0.481
560    0.995       0.3288
570    0.952       0.2076
580    0.87         0.1212
590    0.757       0.0655
600    0.631       0.03315
610    0.503       0.01593
620    0.381       0.00737
630    0.265       0.00333
640    0.175       0.0015
650    0.107       6.77E-4
660    0.061       3.129E-4
670    0.032       1.48E-4
680    0.017       7.15E-5
690    0.0082     3.533E-5
700    0.0041     1.78E-5
710    0.0021     9.14E-6
720    0.00105   4.78E-6
730    5.2E-4     2.546E-6
740    2.5E-4    1.379E-6

（参考资料：http://onlinelibrary.wiley.com/doi/10.1002/0470024275.app7/pdf           https://light-measurement.com/spectral-sensitivity-of-eye/  ）

The colors of the visible spectrum can be broken up into the approximate wavelength values:

      violet and indigo        400-450 nm

      blue and aqua            450-500 nm

      green                          500-570 nm

      yellow-orange            570-610 nm

      red                              610 to approximately 750 nm

      near ultraviolet n-UV  320-400 nm