Basic knowledge of photometry

1, plane angle and solid angle

Definition: The unit of the plane angle is called radians, and the 1 radians is the angle of the circle of 1 m long to the center of the circle. The solid angle unit is called the spherical surface (sr), the 1 spherical surface is the spherical surface with a radius of 1 meter, and the 1 square meter ball faces the solid angle of the spherical center.

2, luminous flux

Definition: Luminous flux is the amount of light emitted by a light source per unit of time, that is, the portion of the effective equivalent that the radiant flux (or radiant power) can be perceived by the human visual system.

Small solution: The luminous flux output from a 40W fluorescent lamp is about 2100 lumens. Luminous flux symbol Φ, in lm;

The luminous efficiency of a common electric light source refers to how much luminous flux 1W of electric power can be converted into.

General efficiency of common light sources (lumens / watts)

Incandescent lamp, 15

Fluorescent lamp, 50

Sodium lamp, 120

3, luminous intensity

Definition: The luminous flux emitted by a light source in a unit solid angle in a given direction is defined as the light intensity (degrees) of the light source in that direction.

Ι = dΦ/dΩ Unit: cd 1cd=1lm/1sr

The actual light source or luminaire has different luminous intensities in all directions. In order to describe the spatial distribution characteristics of its luminescence, it is necessary to express it by a luminous intensity distribution curve (also called a light distribution curve). It is an important basis for lighting calculations and design.

Common light source luminous intensity (cd):

Sun, 2.8E27

Highlight flashlight, 10000

4, illumination

Definition: The illuminance at a point on the surface is the luminous flux dφ incident on the bin containing the point

Divide by the quotient of the bin area dS.

Unit (lx) unit is lux (lx), 1lx=1lm/m2

Common illumination (lux):

Direct sunlight (noon), 110,000 cloudy outdoor, 1000

Inside the mall, under 500 ordinary room lights, 100

Under full moon, 0.2 candle (20cm away), 10-15LUX.

60cm table lamp 60cm tabletop, 300LUX;

Dusk indoor, 10LUX; night street light, 0.1LUX;

5, brightness

Luminance (L, Luminance), in nits, ie nit, or cd/m2.

Definition: The intensity of light emitted by a light source body in a certain direction per unit of projected area.

The brightness of common illuminants (nit):

Sun surface, 2,000,000,000 incandescent filaments, 10,000,000

White paper in the sun, 30,000 eyes can get used to the brightness, 3,000

Full moon surface, 2,500

The human eye can better distinguish the brightness of the color, 1

White paper under the full moon, 0.07 no moon and night sky, 0.0001

Common photometric units and their relationship

o Luminous flux Φ(lm)

o Light intensity I (cd)

o Illumination E (lx)

Edit: Sophy

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