Comparing Energy Efficiency Between Lighting Products

If you switch to LED lighting from an older lighting system, you’re likely to save significant money in energy costs and maintenance. This is true whether you’re replacing money-burning incandescent lights or an antiquated fluorescent lighting scheme.

One of the problems you’ll face when buying LED lights is that, unlike incandescent or halogen technologies, the wattage of the LED fixture or bulb is not a reliable indicator of energy efficiency. In other words, you can’t assume that an LED using more watts emits more light than an LED using fewer watts.

Having converted from an inefficient light source to LED, saving a few extra watts here and there between different LED products is a bit like splitting hairs. But still, if the lights are going to be kept on for a long time (e.g. in a commercial setting or hospital), it makes sense to opt for the most energy-efficient products you can find.

Luckily, there’s an easy way to directly compare the energy efficiency of all light sources. If you take the output of the LED or any kind of bulb in lumens and divide it by the wattage, you’ll be calculating the “luminous efficacy” of the light source. This is a direct indicator of energy efficiency. Here are two examples:

  • A 60W bulb that emits 800 lumens of light has a luminous efficacy of 13.33 lumens per watt (800 divided by 60).
  • A 40W bulb emitting 450 lumens of light would have an efficacy of 11.25 lumens per watt (lm/W) and therefore be less energy-efficient.

The most energy-efficient LED lighting products sometimes achieve an efficacy of over 100 lumens per watt, while less energy-efficient LED products may be 60 lumens per watt. Either, of course, would offer a large saving over the typical incandescent examples given above.

When considering energy efficiency in light fixtures, the design of the fixture has a part to play. One advantage of LED lighting in this respect is that it is naturally directional, which makes it ideal for downlights because light is not needlessly sent in the wrong direction (i.e. upwards).

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