Measuring the photometric quantities of an LED
Article by Dr. Günther Leschhorn
Before the LED started its triumphal march into the lighting industry, the world of light bulbs was relatively simple. A broken 40 Watt bulb was easily replaced in the DIY store. But with LED technology the situation is different: the user is faced with a multitude of new terms such as luminous flux, color temperature or color rendering index (CRI) that are stated on the packaging, but not explained. The purchase of a 40 Watt lamp has thus become a “Check list for the purchase of a new LED lamp from a retailer” . The user must familiarize him- or herself with new values and terms, and expects consistency. That in turn is a challenge for lamp and luminaire manufacturers: How are these quantities correctly measured on a comparable basis? What constitutes a precise measurement?