Ever wondered how induction lighting saves energy? How is it that an 200 watt induction lighting system can replace a 400 watt metal halide lighting system perform better and save energy?
What is pupil lumen:
How people see and are psychologically impacted by lighting has been a subject of much study and discussion for years. Describing light as “lumen output” and measuring it as “foot candles” on a work plane have been the traditional ways of describing and defining how much light is required to perform a variety of tasks. However, that is being re-examined based on results of studies on visual performance and the psychological impacts of lighting. Additionally, the “color rendering index” (CRI) and correlated color temperature (CCT) describe the quality of the light (relating to how true colors appear compared to under a noon north sky on a clear day).
As lighting technology evolves into various types and colors, simply measuring the lumens proves not to be fully adequate in predicting how well people can see. In bright light our pupils contract allowing more detail to be perceived, while depth of field and perceived brightness also increase. In low light our eyes dilate to allow more light in. Sam Berman—formerly with the Lighting Systems Research Group at Lawrence Berkeley Laboratory and a major supporter of the importance of the P/S ratio in lighting selection—developed a conversion factor that applies the P/S ratio to lumen output of various light sources, and then expresses the effective lumens the eye will perceive for vision based on the size of the pupil and the effect on vision (add table 1). Some lamps, like low-pressure sodium, lose most of their output using this method, while others like high-quality induction lamps gain substantially.