The main difference between the illuminance integral method and the intensity method is that it does not require a long measuring distance and is a method for national metrology laboratories in most countries to achieve the total luminous flux benchmark [1]. Figure 3 shows a typical distribution photometer for the ciE 84-1989 recommended illuminance integration method. The LED product under test is located in the rotation center of the photometric detector and maintains a static and stable state in the photometric sampling. The detector directly receives the light beam from the LED product under test, avoiding other intermediate links and achieving a very high total luminous flux measurement accuracy.
At present, major developed countries have completed or competed to study the distribution photometer that USES the illuminance integral method to measure the total luminous flux of LED. The British NPL already has a central-rotating reflector distribution photometer, but for the precise measurement of total light flux and light intensity from small sources such as leds, the NPL USES a distribution photometer based on the illuminance integration method shown in Figure 4.

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