How to measure light intensity

Definition of light intensity:
Light intensity is referred to as light intensity. The international unit is candela, which is short for CD. Other units include candlelight and candlelight. 1CD, i.e. 1000mcd, 1 candela refers to the luminous intensity of light from a monochromatic light source (frequency 540×10 ^ 12Hz) in a given direction (the radiation intensity in this direction is 1 / 683 watt / sphericity). It can be calculated by Kirchhoff integral theorem.

Based on the testing principle of the light distribution curve of the traditional light source, the testing methods for the light intensity distribution of LED devices can be generally divided into two types: one is that the LED is fixed and the photometric detector receiving light rotates and scans around it; The other is that the photometric detector does not move, and the LED rotates and scans around the apex of the package shell. Because these methods have the defects of long test time, low measurement accuracy and cumbersome calibration, a new test method and device are introduced, that is, the light intensity is received by the CCD photometric detector, the light intensity signal is converted into an electrical signal through the photoelectric conversion function of the CCD, and then the light intensity map of the inner wall of the entire hemispherical space can be obtained through the imaging system software. The new testing method has the remarkable advantages of fast testing speed, high accuracy, abundant information and intuitiveness.

1. Rotation method:
The rotation method adds a c-axis on the basis of the traditional light distribution curve test method, which is the line from the physical center of the LED optical axis to the detector center. During the measurement, the c-axis does not rotate, and the v-axis rotates 180 ° to obtain a planar LED light distribution curve. Then rotate the c-axis by a fixed angle (the surveyor can make the graduation by himself), fix the c-axis again and rotate the v-axis, so that the light distribution curve on another plane with different angles can be obtained. After multiple measurements (the number of measurements is related to the size of the c-axis rotation graduation), the light distribution curves of multiple planes in the whole space can be obtained. After computer integration, the complete spatial light intensity distribution curve can be obtained.

This method is based on testing the light intensity distribution curve of the plane first, then setting a rotation axis, and through 360 ° rotation, through multiple measurements at multiple angles, the purpose of obtaining the entire spatial light intensity distribution is achieved. Another rotation method is to set two rotation axes to obtain multiple light distribution curves of different angle planes and integrate them into a spatial light intensity distribution curve. This method is recommended by CIE (International luminous lighting Commission) to test the light intensity distribution of low power light emitting devices.

2. Testing method based on CCD
In this method, CCD image sensor is used as the light detector to obtain the light intensity image of the whole LED light sphere with high accuracy, and then through computer software analysis, a more accurate LED three-dimensional light intensity distribution map can be obtained.

The LED light emitting device to be measured is fixed at the center of the semi-circular chamber, a layer of diffuse reflection coating is coated on the inner surface of the hemispherical measuring chamber, a convex mirror is installed near the center of the hemisphere, a partition is installed between the mirror and the led to isolate the direct light of the LED, and the CCD imaging photometer is placed directly above the mirror. During the measurement, the LED lamp emits light in the hemispherical surface, which is uniformly reflected on the inner surface of the hemisphere through the diffuse reflection coating of the hemispherical wall. The CCD photometric detector can receive the image of the entire hemispherical inner wall reflected by the convex mirror. Because the light intensity at different positions on the inner wall of the hemispherical surface is different, the light signals received by the CCD at different positions on the inner wall of the hemispherical surface are also different. Through the photoelectric conversion function of CCD, the received optical signal is converted into an electrical signal and introduced into the computer. The computer software analyzes and forms a simulated two-dimensional image formed by the convex mirror. Then, through the computer software, the light intensity corresponding to each coordinate of the two-dimensional image and the specific position of the hemispherical inner surface corresponding to each coordinate of the two-dimensional image coordinate system are further analyzed, An accurate spatial light intensity distribution map of the LED in the entire space can be obtained.

Therefore, LISUN lauched the LSG-6000 Moving Detector Goniophotometer (Mirror Type C) was manufactured by LISUN completely meets LM-79-19, IES LM-80-08, COMMISSION DELEGATED REGULATION (EU) 2019/2015, CIE-121, CIE S025, SASO 2902, IS16106 and EN13032-1 clause 6.1.1.3 type 4 requirements. LSG-6000 is the latest upgraded product of LSG-5000 and LSG-3000 in compliance with the requirements of the LM-79-19 standard Clause 7.3.1, its an automatic light distribution intensity 3D curve testing system for measuring light. The measuring distance is from 5m to 30m.

LSG-1890BCCD/LSG-1800ACCD goniospectroradiometer is high precision automatic goniophotometric instrument for luminous intensity distribution measurement with facility for rotating the light source. The LSG-1890BCCD/LSG-1800ACCD can do the spatial CCT test and the intensity distribution test. It is for industrial laboratory photometric data measurement of luminaires such as LED luminaires, LED Plant Lighting, HID luminaires, fluorescent lamps and so on.

Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.

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Tags：LSG-1890B , LSG-1890BCCD , LSG-6000