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Old 11-16-2012, 10:10 AM   #2873
Plenty of seasoning
Joined: Jun 2009
Location: West Nebraska
Oddometer: 964
Muddy waters...

In comparing lights output in Lumens with how many watts they consume, you are comparing the efficiency of the conversion of electrical power to light. Assuming that all the measurements are accurate, if one light puts out more lumens than another for the same wattage, then it is more efficient. The wasted watts don't just disappear however, they are converted into another form of energy, most likely heat. This is why fluorescents and LEDs produce so much more light and are cooler (generally) than halogens and incandescents.

Just because two lamps use the same type of LED (and not that I have done any research on this but I would guess that Cree makes many different grades of LED with different efficiencies and quality control levels) is not the whole story. The electronics package that drives the LED could be more or less efficient too. Less efficient means more heat and heat is the enemy of electronics. So maybe you should look for the lamp that uses the least watts? I doubt that the difference between the best and worst lamps amounts to more than a few watts in the driver board, but that is just opinion, based on the idea that if the board was producing huge amounts of heat in such a small space, even great heat sinking would not save it.

So Lumens per watt is the best way to compare lamps? Wait, there's more mud here. Lumens are a measure of the total light output of a source - in ALL directions. Even if the manufacturers are being truthful and accurate in what they state, the key to performance is getting the photons where you want them - the design and quality of the lens is the main variable here. A better measure of light output in a given direction is Lux, which measures the amount of light falling on a surface. As light from a lamp typically disperses with distance, more so with a flood beam than a spot beam, to compare output between lamps you would have to measure lux at the same distance from the source, and probably pretty close to reduce the errors of beam patterns. So what happens to the light that doesn't go where you want it to? It disperses uselessly (or usefully, depending on what you are trying to illuminate) or it bounces around inside the lamp and creates more heat.

If manufacturers are not quoting Lux, (and some do provide isolux diagrams - Lux maps, if they can be trusted or compared) and everything else is open to interpretation, what is the best way to choose lights. For my money, I guess I would keep wattage iin mind if my electrical supply was marginal...then look at beam patterns, ruggedness, customer satisfaction, return policies etc. that's where sites like advrider are a real resource.
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