As with traditional light sources, the optical units of the LED light source are uniform. In order to make readers understand and easy to use, the following will be a brief introduction to the knowledge:

First, the luminous flux
Luminous flux refers to the amount of light emitted by the light source in the unit time, that is, the radiation energy can be felt by the human eye that part of the radiation energy. It is the product of the radiant energy of a band in a unit time and the relative visual acuity of the band. As the human eye on the different wavelengths of light relative visual rate is different, so different wavelengths of light radiation power is equal, the luminous flux is not equal. The luminous flux symbol is Φ, in lumens (Lm).
LED Light
According to the spectral radiation flux Φ (λ), we can get the luminous flux formula:
 Φ = Km ■ Φ (λ) gV (λ) dλ
 In the formula, V (λ) - relative to the spectral efficiency of light; Km-radiation spectral luminous performance of the maximum value, the unit is Lm / W. In 1977, the Km value was determined to be 683 Lm / W (λm = 555 nm) by the International Metrology Committee.

Second, light intensity
Light intensity refers to the unit of time per unit area through the light energy, energy and frequency is proportional to their strength and the sum (ie integral), can also be understood as the light source in a given direction of the luminous intensity I is the light source The light flux d? Transmitted in the solid angle element in the direction is divided by the solid angle element d ?.
The unit of luminous intensity is candela (cd), 1cd = 1Lm / 1sr. The sum of the light intensities in all directions is the luminous flux.

Third, brightness
We test the brightness of the LED chip and evaluate the safety of LED light radiation process, the general use of imaging, for the chip test can be used to measure the micro-imaging. The brightness is the luminance L at a certain point on the light emitting surface of the light source, the luminous intensity of the face dS in a given direction divided by the quotient of the plane of the face in the plane perpendicular to the given direction
The unit of brightness is candela per square meter (cd / m2). When the light emitting surface is perpendicular to the measuring direction, cosθ = 1.
LED Luminace
Four, light intensity
Illumination is the degree to which the object is illuminated, expressed in terms of the luminous flux received per unit area. The illuminance is related to the illuminated light source, the surface of the illuminated surface and the position of the light source in the space, and the size is proportional to the light intensity of the light source and the incident angle of the light, which is inversely proportional to the square of the distance from the light source to the illuminated surface. The illuminance E on the surface is incident on the luminous flux d? Included in the face element divided by the quota area dS.
The unit is lux (LX), 1LX = 1Lm / m2.

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