We take the "LOR" into its own hands
What is LOR? Well, according to DIN/EN 13032/2, the LOR is described as “the ratio of the luminous flux of the luminaire to the lumens of the lamps used” – pretty simple, eh?
In reality, the light output ratio is a figure that shows how much light gets lost inside the luminaire. It is abbreviated to LOR, and sometimes subdivided into ULOR (Upper Light Output Ratio) or DLOR (Downward Light Output Ratio) – i.e. what percent shines upwards, and what percent, down. You calculate it by dividing the total light output from the luminaire (in lumens), by the total lamp output (also in lumens) to get a percent. For the ULOR and DLOR, you do the same, but with the light that comes from the upper and lower halves of the luminaire.
So calculating it is easy, understanding it is less straightforward. With a bare lightbulb, apart from the ‘bayonet’ part of it, light comes out in all directions. Put it inside a lampshade, and some light gets lost. Put it inside a high-tech reflective luminaire, and light still gets lost. This seems a little crazy – surely the mirrored reflector in the luminaire would reflect all the light out? Well, in a word, no – mirrors actually absorb light! If you look at the reflection of a torch in the mirror, it won’t be as bright as the torch itself. So some luminaires trap light.
Knowing this, you would automatically choose the light with the highest output ratio, right? Well not necessarily. The following examples explain some of the pitfalls of the LOR:
This bare incandescent bulb looks great on a beach, doesn’t it? Set in a lamp holder it will have one of the highest, and best LORs. However this naughty bulb produces a puny 7 lm/W, so would be a very poor choice. Lamp efficiency is equally, if not more important, to light output ratio.
This downlight has a phenomenal LOR of 99%. This is because the manufacturer is being cheeky with the definition of ‘lamp’ and classifying it as most of the luminaire. In fairness, it is hard to apply the term ‘LOR’ to LED fittings because the light source and luminaire are so interlinked. The term is more meaningful with futureproof luminaires where the LEDs come on small replaceable modules.
My final examples, above and below, show where LOR is really useful. At 96%, compared with 76%, the lamp above would be a more energy efficient choice. Having an upper light output, i.e. lighting the ceiling, will make the room feel less gloomy in both instances. Combined with good task illumination, both lights would be an excellent choice for a lecture room or office.
The light output ratio is one of many factors that lighting designers consider when selecting a luminaire. When used well and understood correctly, it can be an excellent tool to produce energy efficient lighting schemes with a pleasing balance of light.