Lux (lux, legal symbol lx) illuminance unit, 1 lux is equal to 1 lumen (lumen, lm) luminous flux evenly distributed over 1m2 area of illuminance. Lux is the “light” in Latin.

The definition of LUX

The lux (symbol: lx) is the SI derived unit of illuminance and luminous emittance, measuring luminous flux per unit area.It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, “lux” is used as both the singular and plural form.

Illuminance is a unit that reflects the intensity of light. Its physical meaning is the luminous flux per unit area. The unit of illumination is the number of lumens per square meter (Lm), also known as Lux: 1 lx=1 Lm/m2 In the above formula, Lm is a unit of luminous flux, which is defined as the amount of light radiated by a surface area of 1/60 square meters of pure platinum at a melting temperature (about 1770 ° C) within a solid angle of 1 steradian.

In order to have a perceptual understanding of the amount of contrast, the following calculation is performed. A 100W incandescent lamp emits a total luminous flux of about 1200 Lm. If the luminous flux is uniformly distributed on the half sphere, then the source is The illuminance values at 1m and 5m can be obtained by the following steps: The area of the hemisphere with a radius of 1 m is 2π × 1^2 = 6.28 square meters. The illuminance value at 1 m from the light source is:1200 Lm / 6.28 square meters = 191 lx For the same reason, the area of the hemisphere with a radius of 5 m is: 2π × 5 ^ 2 = 157 square meters. The illuminance value at 5 m from the light source is: 1200 Lm / 157 square meters = 7.64 lx

It can be seen that the illuminance emitted from the point source is obeying the inverse square law.

1 lx is approximately equal to the illumination of 1 candle at a distance of 1 meter. The minimum illumination (MINIMUM.ILLUMINATION) that we have in the camera parameter specification means that the camera can obtain clear image images only under the indicated LUX value. The smaller the value, the better, indicating that the sensitivity of the CCD is higher. Under the same conditions, the black-and-white camera requires much 10 times less illumination than a color camera that still has to handle color density.

General conditions: 100,000 lx in summer sunshine; 10000 lx in cloudy day; 100 lx in indoor fluorescent lamp; 300 lx in 60 CM tabletop from 60W table lamp; 1000 lx in TV station studio; 10 lx in twilight room; 0.1 lx; candlelight (20CM far) 10~15 lx.

Sunlight provides between many thousand of lux to only a few hundred depending on the weather conditions & time of day. The lux of artificial indoor lighting, however, is typically 1000 lux or below, as can be seen in the following commercial lighting installation examples:

EnvironmentTypical Lux
Hospital Theatre1,000
Supermarket, Sports Hall750
Factory, Workshop750
Office, Show Rooms, Laboratories, Kitchens500