How do you select LEDs since we are not used to thinking in lumens?
An incadescent 60 watt bulb puts out about 800 lumens.
When the only light bulbs we knew were incandescent, wattage was an okay method to think about brightness.
But when alternatives like fluorescent and LED became more popular, that gauge no longer made sense.
- That’s because wattage doesn’t measure light output; it measures the flow of electricity.
- As light sources have become more efficient, they can emit more light using smaller amounts of electricity, i.e. using lower wattage.
If you’ve purchased CFLs, you know that a 23 watt CFL is roughly equivalent to a 100 watt incandescent. That reflects the fact that CFLs are about four times as efficient – they use a quarter of the electricity to make the same amount of light. LEDs are even more efficient.
Selecting a light bulb
What we really want to know in selecting a light bulb is, as you mention, its lumen output. Actually, that’s not entirely true. We want to know its lumen output as well as its wattage and a few other things that tell us what the quality of light is.
The Green Home Guide has talked about those other things -- color temperature and color rendering index -- here.
In terms of brightness, though, here are some rules of thumb, courtesy of CleanTechnica.com, for buying replacement light bulbs:
- To replace a 100-watt incandescent bulb, look for a bulb that gives you about 1600 lumens. If you want something dimmer, go for fewer lumens; if you prefer brighter light, look for more lumens.
- Replace a 75W bulb with an energy-saving bulb that gives you about 1100 lumens.
- Replace a 60W bulb with an energy-saving bulb that gives you about 800 lumens.
- Replace a 40W bulb with an energy-saving bulb that gives you about 450 lumens.
It’s only when we know both the wattage and lumens of a bulb that we can know both how bright and how energy efficient it will be.
- A 60 watt incandescent bulb will emit about 800 lumens. That means it makes about 13 lumens per watt (LPW).
- A CFL that ouputs the same brightness will use about 13 – 18 watts, giving it an LPW of around 50.
- And an 800 lumen LED will consume about 8 - 13 watts, meaning its LPW is over 75. (LED efficiencies are still increasing as the technology evolves.)
Fortunately, all this information – as tedious as it may sound – is fairly easy to come by.
Look for the Lighting Facts label
More and more light bulbs include a “Lighting Facts” label on their packaging.
It looks like this and tells you pretty much all you need to know: