Sibbo wrote:
Major , for we LED newbies , what are we lookin for ? Lumens is the unit of brightness ? How many ,how do I judge from an ad ?
Yes, Sibbo, Lumens is a measure of light output, rather than watts, which is a measure of how much electrical power the lamp uses (kind of - I know, watts is really a measure of "work" over time, but we use it in the electrical world to represent an amount of electrical power - kind of).
Just as Halogen lights put out more light per watt than the "conventional" incandescents that preceded them (Halogens are also incandescents), LED's put out even more light per watt. Plus, unlike Halogens and other incandescents, LED'S produce very little heat. Incandescence is, in fact, literally the process of producing light by heating something until it glows.
There are various levels of LED's, and they all produce different amounts of light per watt. The really bright ones cost a lot more than the simple "first generation" LED's. As far as telling what exactly you are getting from an ad, there are two issues:
1) What does the ad tell you?
2) Can you believe them?
In the ad for the lights we're talking about here, they just don't tell you, so there is no way to identify just how bright they are. Some sources list the Lumens per Watt for LED's as varying from 4.5–150! So, there's a very wide range. Halogens put out around 25 per watt.
If you go to a site like
http://www.surefire.com/, they will give you very clear numbers on the the specifications for their flashlights, but, when you're looking at something on eBay, unless it comes from some well known manufacturer, you have absolutely no way to know what the product specs are. They often don't tell you, and if they do, you have no idea if you can believe them.
All of that is just about the lamp - the light "source," but, as The Bigfella says, reflector (and lens) design are extremely important factors in how any spotlight works, and headlights have very specific requirements for good reflector and lens design, with different needs for low beam and high beam, especially with the control issues that the low beam presents. A well designed reflector/lens system can put 4 or 5 times as much light out in front of you where you need it as a poor one (with both using the exact same lamp), and the well designed one will also have much more even coverage than a poor one.