The internal reflection characteristic of integrating sphere is one of the key factors that make the LED directivity affect the measurement accuracy. In the ordinary LED test system, the reflectivity and lambert properties of the surface coating of the integrating sphere are not ideal. One reason is low reflectivity, the other is poor diffuse reflection characteristics. The result of the low reflectivity of the surface of the integrating sphere is the direct light of the LED. The result is that the direct light of the LED gradually decays after several reflections. However, a large proportion of both direct and reflected light is dominant in the overall blending process. In some cases, low reflectivity materials can produce a strong shadow effect on the back side of the baffle probe. However, it is the light and shadow effect of the straight line that causes the measurement to be inaccurate.

In addition, low diffuse reflectance will seriously affect signal attenuation. In the process of light measurement, the light is reflected several times in the integrating sphere, and each reflection will produce a certain attenuation, but the influence of reflection on light intensity is strengthened after multiple reflections. For example, the reflected light is reflected 15 times in the integrating sphere, and if there is a 5% difference in the reflectivity, the signal attenuation may more than double. In fact, the reflectivity of the integrating sphere varies much more than this.
Current LED testing systems do not have standard LEDs that are used as standard light sources. In the measurement process, we still choose to use the standard halogen tungsten lamp as the standard light source. Because the external structure of the standard lamp and the measurement LED is very different, including the light absorption effect of the LED lamp holder and the difference between the standard lamp installation and the LED installation location, all of these are important factors that affect the accuracy of the test results.

Source: China Lighting Network