In the field of optical metrology, luminous flux is an important index to characterize the quality of electric light source.
Currently, the majority of luminous flux measurement is based on the integrating sphere method, so measurement
accuracy of integrating sphere is the key factor. There are plenty of factors affecting the measurement accuracy, such as
coating, power and the position of light source. However, the baffle which is a key part of integrating sphere has
important effects on the measurement results. The paper analyzes in detail the principle of an ideal integrating sphere.
We use moving rail to change the relative position of baffle and light source inside the sphere. By experiments, measured
luminous flux values at different distances between the light source and baffle are obtained, which we used to take
analysis of the effects of different baffle position on the measurement. By theoretical calculation, computer simulation
and experiment, we obtain the optimum position of baffle for luminous flux measurements. Based on the whole luminous
flux measurement error analysis, we develop the methods and apparatus to improve the luminous flux measurement
accuracy and reliability. It makes our unifying and transferring work of the luminous flux more accurate in East China
and provides effective protection for our traceability system.