Requirements for the use of light meters:
① Photocells use selenium (Se) photocells or silicon (Si) photocells with good linearity; they can maintain good stability after long-term operation, and have high sensitivity; when high E, choose high internal resistance photocells, which have low sensitivity and good linearity , not easily damaged by strong light exposure
②There is a V(λ) correction filter inside, which is suitable for the illumination of different color temperature light sources, and the error is small
③Add a cosine angle compensator (opal white glass or white plastic) in front of the photocell because when the incident angle is large, the photocell deviates from the cosine law
④The illuminometer should work at room temperature or close to room temperature (photocell drift changes with temperature)
