F

Fading
A change in colour, usually to a lighter and less saturated colour.

Fechner's law

Federal colour card (for paint)

Flat

Fluorescence
A process by which radiant flux of certain wavelengths is absorbed and reradiated nonthermally at another, usually longer wavelengths.

Fluorescent
Exhibiting fluorescence.

Fluorescent whitening agent
Fluorescent dye or pigment that absorbs near ultraviolet radiant flux and re-emits the power as visible light (violet-blue), causing a whiter appearance when added to a yellowish-white material.

Flux (luminous)
The time rate of flow of light energy; luminous power.

Flux (radiant)
The time rate of flow of radiant energy; radiant power

Fong equation
An equation that convers the Y tristimulus value into a more visually linear scale, used in the BFD(l:c) colour difference formula. The equation is as follows:

Foss colour order system

Fovea pit

Fresnel law of reflection
Sometimes referred to as Weber's law or Weber-Fechner's law states that to be just noticeably brighter, one patch of light must exceed in luminance that of another by a constant fraction. If one patch of light has a luminance L and the other a luminance L + dL, where dL is a just noticeable difference, the ratio dL/L is constant.

Friele line element

Full colour

Full radiator
See Blackbody.

Full shade