Optical trivia

luminous flux

The energy radiated by a light source to the surrounding space per unit time and causing visual effects is called luminous flux. Light is expressed in lumens (lm). The luminous flux is related to both the radiation intensity of the light source and the wavelength. The human eye is most sensitive to yellow and green light with a wavelength of 555nm.

brightness

The luminous intensity and brightness of a luminous body in a given direction per unit projected area, denoted as L, in candela per square meter. ( CD/M2 )

The brightness of the luminous body in the direction of the sun is L=l0/Scos θ

The brightness of an object is related to the intensity of the light source and also to the object's reflection ability.

color temperature

When the color emitted by a light source is the same as the color emitted by a blackbody heated to a certain temperature, it is called the color temperature of the light source, abbreviated as color temperature.

Color Rendering Index

The average value of the CIE1974 special color rendering index for a set of eight color samples, commonly known as the color rendering index. The symbol is Ra. Cold light sources use chemical and electrical energy to excite light sources, such as LED, HID, EL, energy-saving lamps, optical flux, fluorescent lamps, etc. Thermal light source refers to a light source that is excited by thermal energy, such as incandescent lamps, halogen lamps, high-pressure mercury lamps, metal halide lamps, etc.