The absolute luminous flux integrator (ALFI), available from Photometric Solutions International , is a device designed for absolute measurement of luminous flux of lamps. The absolute luminous flux integrator (ALFI) secondary use is also to measure the luminous intensity distribution of small lamps.
The lamp is placed in a rotating lamp holder in the centre of the device. A photocell is mounted on an arm which rotates about the lamp. The lamps rotation presents different azimuth angles to the photocell, while the photocell sees different elevation angles of the lamp as it revolves around it. By rotating through all of the azimuth angles and executing a sweep of the elevation angles within each azimuth angle plane, the luminous flux is summed over the whole sphere around the lamp.
During the process of a luminous flux measurement, the ALFI measures illuminance, E, from the lamp in all of those directions at the test distance, d. The distribution of the luminous intensity, I, can also be derived from these measurements. Because the test distance is small, the calculation of the luminous intensity is only valid if the size of the test item is one-fifth of the test distance or less (the length of the photocell arm). This is a general rule of thumb of photometry for near-lambertian sources called the 1:5 rule.
The overall device is designed to fit into a standard room height of 2.7m. The test distance, or radius of rotation of the photocell, is 1.0m standard. This means that the luminous intensity distribution of lamps of up to 200mm can be measured. These are the standard dimensions of these devices, however they can be scaled to fit into a larger room size if required.