1. Detection of luminous intensity

The intensity of light, the intensity of light, refers to the amount of light emitted at a specific angle. Because the LED light is concentrated, the inverse square ratio law is not applicable at close range. The CIE127 standard provides two conditions for measuring the average normal light intensity: the measurement condition A (far field condition) and the measurement condition B (near field condition). The detector area of the two conditions is 1 cm 2. Usually, luminescence intensity is measured using standard B.

2. Luminous flux and luminous efficiency detection

Luminous flux is the sum of the amount of light emitted by a light source, that is, the amount of light emitted. The detection methods mainly include the following 2 kinds:

(1) integral method. The standard lamp and the measured lamp are ignited successively in the integrating sphere, and their readings in the photoelectric converter are recorded as Es and ED, respectively. The standard lamp's luminous flux is known to be s, and the luminous flux of the measured lamp is D=ED s/Es. The integral method is based on the principle of "point light source". It is easy to operate, but it is influenced by the color temperature deviation between the standard lamp and the measured lamp.

(2) spectroscopic method. The luminous flux is calculated by spectral energy P (lambda) distribution. A monochromator is used to measure the 380nm ~ 780nm spectrum of the standard lamp in the integrating sphere. Then the spectrum of the lamp under the same condition is measured and the luminous flux of the lamp under test is calculated.

The luminous efficiency is the ratio of the luminous flux emitted by the light source to the power consumed. The luminous efficiency of LED is usually measured by constant current method.

3, spectral characteristics detection

The spectral characteristics of LED include spectral power distribution, color coordinates, color temperature, color rendering index and so on.

Spectral power distribution indicates that the light source is composed of many different wavelengths of color radiation, and the radiation power of each wavelength is different. This difference is called the spectral power distribution of the light source. The light source was compared and measured by spectroscopic Photometer (monochromator) and standard lamp.

The chromatic coordinates represent the amount of luminous color of the light source in digital coordinates. There are many coordinate systems to represent color coordinates, usually using X and Y coordinate systems.

The color temperature is the amount of the color table (appearance color) that the human eye sees. When the color of light emitted by a light source is the same as that emitted by an absolute black body at a certain temperature, the temperature is the color temperature. In the field of lighting, color temperature is an important parameter to describe the optical characteristics of light source. The theory of color temperature originates from blackbody radiation and can be obtained from the color coordinates of the light source containing the blackbody trajectory.

The color rendering index indicates the amount of light emitted by a light source that correctly reflects the color of the object being illuminated. It is usually expressed by the general color rendering index Ra, which is the arithmetic average of the color rendering index of the light source to eight color samples. Color rendering index is an important parameter of light source quality. It determines the application range of light source. Improving the color rendering index of white LED is one of the important tasks of LED research and development.

4. Light intensity distribution test

The relationship between light intensity and spatial angle (direction) is called pseudo light intensity distribution, and the closed curve formed by this distribution is called light intensity distribution curve. Because there are many measuring points and each point is processed by data, the automatic distributed photometer is usually used for measuring.

5. Effect of temperature effect on optical properties of LED

Temperature will affect the optical properties of LED. A large number of experiments show that temperature affects the emission spectrum and color coordinates of LED.

6. Surface brightness measurement

The luminance of a light source in a certain direction is the luminous intensity of the light source on the unit projection area in that direction. Generally, surface luminosity is measured by a surface luminosity meter and a aiming luminosity meter. There are two parts: the aiming light path and the measuring light path.