What is called the lumen, what is flux, what is new lux

1967 France Thirteenth International Conference provides metering to cd , cd / m², lumens, lux , respectively, as the unit of luminous intensity , brightness , flux and other illumination optical unit of measurement used in unified engineering technology has important significance. To enable you to understand and ease of use , the following knowledge will make a brief introduction :

1 candlelight , international candle , cd (candela) definition

101325 in Newton per square meter standard atmospheric pressure , an area equal to 1 / 60 cm2 absolute "bold" ( i.e., capable of absorbing all of the external light reflected from the object is no ideal ) , pure platinum (Pt) solidification temperature ( about 2042K was 1769 ℃) , the luminous intensity in the vertical direction is 1 candela . Also, the candlelight , the International Candlelight, Candela three concepts are different , not equal . In terms of volume , equal to 58.8 cd 60 international candle , light a candle hefner international candle equals 0.885 or 0.919 candela .

A light emitting intensity and brightness

Luminous intensity of light intensity for short , the international unit is candela ( cd ) abbreviated cd. Lcd is the luminous flux emitted by the light source in the specified direction unit solid angle . The radiation source is uniform , the light intensity is I = F / Ω, Ω is the solid angle , in units of steradian (sr), F is the luminous flux , in units of lumens from the light source to the point I = F / 4. The brightness is the brightness of the light emitting surface of the light emitting surface is the ratio of the luminous intensity in a given direction and the direction perpendicular to the light emitting surface of the specified area , the unit is candela / square meter. For a diffuse scattering surface , although the light intensity and the luminous flux in all directions , but the brightness is equal in all directions . TV screen that is similar to the diffuse scattering surface , the image viewed from all directions , have the same sense of brightness .

The following is a portion of the light source luminance values ​​: Unit cd / m²

Sun: 1.5 * 10 ; Fluorescent : (5-10) * 10 ³; moon ( full moon ): 2.5 * 10 ³; black and white TV screen : about 120 ; color TV screen : 80 or so .

3 lumens luminous flux

Light emitted by the light source is radiated in all directions , for a unit time by the area of ​​light, known as the area through which the flux of radiant energy . Different frequencies of light colored eyes are sensitive to different colors of light , even if the colored light energy flux equal, and does not produce the same visual brightness level of the light in the colors yellow , green light aroused maximum brightness sensation . If the green light as standard , making it radiant flux equal to the flux , the shade on the other , the ability to evoke the feeling of a bright light is smaller than the green, the luminous flux is smaller than the energy flux . The unit of luminous flux is the lumen , is a transliteration of the English lumen , abbreviated lm. Absolute blackbody at the solidification temperature of platinum , radiation from the 5.305 * 10 ³ cm ² area out of the flux is 1lm. To show the relationship between light intensity and luminous flux , luminous intensity of 1 candela point light flux emitted per unit solid angle (1 steradian ) within 1 six . The output of a 40W fluorescent lamp luminous flux is about 2100 lumens.

4 lux illumination and

Illumination available illuminometer measured directly. Illumination unit is lux lux is the English transliteration can also be written as lx. The object is irradiated with uniform light , the area of ​​1 m2 is obtained by a lumen flux when it is 1 lux illumination . Sometimes, in order to fully utilize the light source in the light source is often an additional reflection means , so that the direction can be more certain of the flux to increase the illumination of the illuminated surface . Such as car headlights , flashlights, photographic lights.

The following are the various environmental illuminance values ​​: Unit lux

Night 0.001 0.02 ; Moonlight 0.02 - 0.3 ; cloudy indoor :5 ​​-50 ; cloudy outdoor :50 -500 ; sunny indoor :100 -1000 ; illumination under the summer sun at noon : about 10 * 9 th ; the required illumination when reading books :50 -60 ; standard home video camera illumination: 1400 .