What is the light intensity of a lamp generally expressed by?

Light intensity/Candeira, brightness /cd/m? 0? 5. luminous flux/lumen, illuminance/lux [published by Lin Muding on May 30, 2006 12: 56: 00]

1967 The 13th French International Metrology Conference stipulated that Candeira, Candeira /m2, lumen and lux should be used as the units of luminous intensity, brightness, luminous flux and illuminance respectively, which is of great significance to unify the optical measurement units used in engineering technology. In order to facilitate understanding and use, the following briefly introduces the relevant knowledge:

Definition of name unit symbol

Light intensity cd

candela

(Candeira) I = f/Ω luminous flux emitted by a light source in a specified direction within a unit solid angle.

Brightness cd/m? 0? 5 denotes the brightness of the light-emitting surface, and refers to the ratio of the luminous intensity of the light-emitting surface in the specified direction to the area of the light-emitting surface perpendicular to the specified direction.

Luminous flux lm

lumen

(Lumens) f The light energy passing through an area per unit time is called the radiant energy flux passing through this area.

Absolute blackbody at the solidification temperature of platinum, from 5.305* 10? 0? 6cm？ 0? The luminous flux radiated by area 5 is 1lm.

In order to show the relationship between light intensity and luminous flux, a point light source with light intensity of 1cd emits luminous flux of 1 lm in unit solid angle (1sphericity).

Illuminance lx

lux

(Lux) Is the object uniformly illuminated by light at a distance of 1m from the light source, or at a distance of 1m? 0? When the light flux in the area of 5 is 1lm, its illuminance is 1lux.

Commonly known as "candlelight table".

1. Definition of candlelight, international candlelight and Candeira.

Under the standard atmospheric pressure of 10 1325 Newton per square meter, an absolute "blackbody" with an area equal to 1/60 square centimeters (that is, an ideal object that can absorb all external light without reflecting) is at the solidification temperature of pure platinum (about 2042K to1769) Moreover, the three concepts of candlelight, international candlelight and Candeira are different and should not be equated. In terms of quantity, 60 Candeira is equal to 58.8 international candle, and the 1 candle of Hefner lamp is equal to 0.885 international candle or 0.9 19 Candeira.

2. Luminous intensity and brightness

The luminous intensity is referred to as light intensity, and the international unit is Candeira (abbreviated as Candeira) cd. Lcd refers to the luminous flux emitted by a light source in a specified direction within a unit solid angle. When the light source radiates uniformly, the light intensity is I = f/ω, ω is the solid angle, and the unit is sphericity (sr). F is the luminous flux, and the unit is lumen. For point light source, I=F/4. Brightness refers to the brightness of the light-emitting surface, which refers to the ratio of the luminous intensity of the light-emitting surface in the specified direction to the area of the light-emitting surface perpendicular to the specified direction, and the unit is candela per square meter. For diffuse reflection surfaces, although the light intensity and luminous flux in all directions are different, the brightness in all directions is equal. The screen of a TV is similar to such a diffuse surface, so when you look at the image from all directions, you will have the same brightness.

The following are the brightness values of some light sources: unit cd/m? 0? five

Sun:1.5 *10; Fluorescent lamp: (5- 10) * 10? 0? 6; Moonlight (full moon): 2.5* 10? 0? 6; Black and white TV screen: about120; Color TV screen: about 80.

3. Luminous flux and lumen

The light energy emitted by the light source radiates in all directions, and the light energy passing through a certain area in unit time is called the radiant energy flux passing through the area. The sensitivity of eyes to different colors of light varies with frequency. Even if the radiant energy flux of different colors of light is equal, it cannot produce the same brightness visually. Among all colors of light, yellow and green light can cause the feeling of brightness most. If green light is taken as the standard, its luminous flux is equal to radiant energy flux. For other colors of light, the ability to arouse brightness is less than green light, and the luminous flux is also less than radiant energy flux. The unit of luminous flux is lumen, which is the transliteration of English lumen, abbreviated as lm. Absolute blackbody at the solidification temperature of platinum, from 5.305* 10? 0? 6cm？ 0? The luminous flux radiated by area 5 is 1lm. In order to express the relationship between light intensity and luminous flux, the luminous flux of a point light source with light intensity of 1 Candeira in unit solid angle (1 sphericity) is 1. The output luminous flux of 40W fluorescent lamp is about 2 100 lumens.

4. Illumination and lux

Illuminance can be measured directly with an illuminance meter. The unit of illumination is lux, which is a transliteration of English lux and can also be written as lx. When the light flux of the illuminated object is 1 lumen in the area of 1 square meter, its illuminance is 1 lux. Sometimes, in order to make full use of the light source, a reflective device is often attached to the light source, so that more luminous flux can be obtained in some directions to increase the illumination on the illuminated surface. Such as car headlights, flashlight, photographic lamp, etc.

The following are various ambient lighting values: lux.

Night: 0.001-0.02; Moonlit night: 0.02-0.3; Indoor cloudy: 5-50; Outside on cloudy days: 50-500; Indoor in sunny days:100-1000; Illuminance under midday sunlight in summer: about 10*9 power; Illumination required for reading books and periodicals: 50-60; Standard illuminance of home camera: 1400.