Graphical illuminance, luminous flux, and light intensity
The luminous flux is an index indicating the overall brightness of the light source. The unit is lm (lumen). It is often used when indicating the brightness of the illumination source. It is a reference to the sensitivity (visual sensitivity) of the human eye to indicate the physical quantity of the light emitted by the light source. The specific value is that the light flux of the isotropic light source having a luminous intensity of 1 cd (candela) is 1 lm in a solid angle of 1 sr (stereo radiance). Here, sr is a unit of a solid angle, and indicates an apex angle of a cone of a square (r2) having a radius (r) from an area of ​​the sphere facing the center of the sphere.
The luminous flux is an index indicating the overall brightness of the light source. The unit is lm (lumen). It is often used when indicating glare of a display LED or the like. It is defined as: a 540×1012 Hz (wavelength 555 nm) frequency monochromatic light is emitted, and a light source having a intensity of 1/683 W/sr is emitted in a specified direction, and the light intensity in this direction is defined as 1 cd.
The brightness is an index indicating the intensity of light emitted from the secondary light source such as the light source and the reflecting surface and the transmitting surface to the observer. The unit is cd/m2. Like the luminous flux, it is a physical quantity expressed in combination with the sensitivity of the human eye. Most of them are used when indicating the brightness of a display screen such as a liquid crystal panel or a PDP.
Illuminance is an indicator of the brightness of light that is incident on a plane. The unit is lx (lux) and is sometimes labeled lm/m2. It refers to the luminous flux per unit area of ​​the luminous flux of the light source that is directed toward the planar object. It is used to compare the brightness of the lighting fixture on the plane.
The relationship between luminous flux, light intensity, brightness, and illuminance is simply summarized as follows: the luminous flux divided by the unit solid angle is equal to the light intensity; the luminous flux divided by the unit area is equal to the illuminance, and the light intensity divided by the unit area is equal to the brightness.
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