When studying lighting fixtures or directional light sources, the most critical question is:
How light is distributed at different angles. This is known as luminous intensity distribution measurement.
Common measurement methods use a goniometer or goniophotometer. The principle is relatively simple:
1. Mount a photocell at the end of a long arm or a curved track.
2. Allow it to rotate around the illuminator, recording the light intensity at different angles.
3. The illuminator itself is mounted on a rotatable plate, allowing precise azimuth readings.
There are several key points to note:
1. Optical path requirement: The distance from the light source to the photocell must be at least five times the maximum dimension of the light source to avoid near-field effects.
2. Operating position: The illuminator must be illuminated at its designed operating position. Fluorescent lamps, in particular, can be operated at a different position, affecting not only light output but also temperature.
3. Spatial conditions: Experiments should be conducted in a darkroom, with strict control to prevent stray light from entering the photocell.
4. Methods for reducing instrument size: If you don't want an overly large device, you can use mirrors to "fold" the optical path, thereby extending the optical path without taking up too much space.
Finally, what is measured is actually the relative light intensity at various angles, which can be obtained by reading the photocurrent value. Calibration is required to ensure reliable data.