In photometry,<unk>  is a measure of the wavelength-weighted power emitted by a light source in a particular direction, based on the<unk> ity function, a standardized model of the sensitivity of the human eye. The SI unit of<unk>  is the candela (cd), an SI base unit.
Photometry deals with the measurement of visible light as perceived by human eyes. The human eye can only see light in the visible spectrum and has different sensitivities to light of different wavelengths within the spectrum. When adapted for bright conditions (photopic vision), the eye is most sensitive to greenish-yellow light at 555 nm. Light with the same radiant intensity at other wavelengths has a lower<unk> . The curve which measures the response of the human eye to light is a defined standard, known as the<unk> ity function. This curve, denoted 
V
(
λ
)
{\displaystyle V(\lambda )}
 or 
y
¯
(
λ
)
{\displaystyle {\overline {y}}(\lambda )}
, is based on an average of widely differing experimental data from scientists using different measurement techniques. For instance, the measured responses of the eye to violet light varied by a factor of ten.<unk>  should not be confused with another photometric unit,<unk>  flux, which is the total perceived power emitted in all directions.<unk>  is the perceived power per unit solid angle.<unk>  is also not the same as the radiant intensity, the corresponding objective physical quantity used in the measurement science of radiometry.
Luminous intensity
Itch
Density
Fluency
Stripping
Palpitation causes
Breathe odor
Intensity 