If you want to test light sources - integrating sphere and goniophotometer are very important instruments

Light Measurement: Integrating Sphere and Goniophotometer

Integrating sphere and Goniophotometer mesurement.
The integrating sphere can measure the total light output of a lamp quickly without inaccuracy.but there is certain requirement for the position of the lamp when it is being tested,for example,the lamp being tested has to be placed in the center of the integrating sphere. Moreover,there is a light meter on one side of the integrating sphere ,it is used to measure the light output of the lamp. There is a baffle between the lamp and the light meter which is to stop the light meter from seeing any direct light from the lamp.The inside of the integrating sphere (including the baffle) is coated with a very white paint ,the white paint can reflect all wavelengths equally. This allows us to get the correct measurement values we want.
It is crucial that there is nothing else in the integrating sphere besides the lamp and the baffle. If anything else is placed in the sphere, like a fixture, would absorb some of the light. So that is to say,something  besides the lamp and baffle is placed in the sphere, not all of the light reaches the light meter and this leads to wrong meter readings. This means that we can only obtain "bare lamp" readings in the   integrating sphere. The integrating sphere cannot measure the light output of the lamp in fixture (which the goniophotometer can).