The integrating sphere will homogenize the light emitted by the light source so that the light on the inner surface of the sphere is consistent, so that the luminous flux of the light source is obtained by measuring the illuminance value per unit area by the inner surface area. It can be seen that the uniformity of light distribution is an important index to determine the accuracy of measurement results. Relative to the surrounding light uniform incandescent, energy-saving lamps, the LED because of its strong direction, and relatively special. This makes the LED direct light on the surface of the integrated sphere was unevenly distributed, directly lead to different direct reflection of the LED relative to the detector reflection characteristics are different.
Because the position of the detector port and the setting of the baffle are fixed, the different reflection distributions are directly expressed as signal fluctuations. According to the verification results, the general LED measurement system LED placement direction of the luminous flux measurement results often more than 50%.
An important reason for the influence of the LED's orientation on the measurement accuracy is the internal surface reflection of the integrating sphere. In the conventional LED measurement system, the reflectance and Lambertian properties of the integrating sphere surface coating are not ideal. One is the low reflectivity, the other is the diffuse reflection is not good.
One of the manifestations of this integrating sphere is that the direct light of the LED is gradually attenuated after a few reflections, and the direct exposure to light and direct reflection takes a large proportion during the entire light mixing process The leading role. Under certain conditions, the rear of the baffle detector will have a strong shadow effect.
In the design of LED measurement system, according to the actual use of the measurement accuracy of the factors to be fully optimized to make the system to the LED direction of the sensitivity to a minimum.
That is, in the measurement process, no need to specify a special angle and direction. Even in extreme conditions, the use of highly directional LEDs, the use of extreme conditions of the placement of the measurement results still maintain a good consistency.
The design of the baffle and the detection port was optimized using a diffuser to minimize the sensitivity of the probe port to direct reflection of light.