The lumen – candela ratio
Singapore, 23rd November 2012
You always learn or realise something new, even after 30 years in the business. Today as a new product range was introduced to me by one of my suppliers the issue of quality and performance came prominently into the discussion. With several experiences with ruthless LED Cowboys still fresh in my mind, making sure the manufacturer and his local supplier are experienced and know what they talk about is of prime determination in whether to decide to do further business together.
In comparing their product to competitive equivalents from some well established brands, they brought in the so called lumen-candela ratio. Always on the outlook for relevant performance criteria to best log in our specifications (and fend ourselves from the LED Cowboys) I found this a really interesting criteria. Nothing new really and similar to what we have always used in terms of describing a lamp/luminaire efficiency or light output ratio, but somehow pushed to the background in the fast evolving LED market.
Because of the compactness of the LED technology and the way light is emitted we have been assuming so far that most of the light emission is channelled into actual useful light. But with lens technology moving forwards in big leaps as well, we find ourselves in a situation where the optics are becoming an as important part of the final performance. So on one hand we have the actual lumens per watt production from the LED chip but on the other hand we have the optical efficiency in transmitting those lumens into s high performing directional beam of light, measured in candela’s…hence the lumen-candela ratio.
What I discovered is that a product with a lower lumen package can still outperform a higher lumen package by its high quality lens conversion. In a particular example I found that although the product had only about half the lumen package it produced a 30% higher candela value. And yes the product and beam shapes were identical. Interesting, and something to seriously consider in our specifications to root out the Cowboys!
Light Watch 3-182: Below one of my earlier sketches explaining the relationship between lumens and candela’s, how lenses can convert a beam and some product pics. Have a great weekend! 🙂