Convertions from Watts to Candle Pwr to Lumen?

As you can probably guess /ubbthreads/images/graemlins/wink.gif, I've been cruising the web looking at various flashlight sites. Everyone seems to use different measures of light output to make it harder to compare them against each other. I know you need to know more then sheer light "power" but, I still would like to know the relative quantities of light involved.

Specifically, the SureFire L4 LED light is advertised as 5 watts. How much light is this? Is it 65 lumens like the other SureFires? Then Streamlight has those 40,000 Candle Power Stinger HP's.

How do you do the math to level the playing field?

THANKS!

I'm sorry I can't be more specific as I don't know, but I recall reading that candlepower and lumens are two entirely different things and simply cannot possibly be converted from one to the other.

That is consistent with my general thoughts as a "watt" is a measure of energy or work. Lumen and Candle Power is a different entity completely to my weak knowledge of the subject matter at hand.

It almost seems like a snake oil sales pitch at times when a manufacturer uses a completely different measurement unit in their own line.

42 vs. 40,000 Candle Power I can understand.

5 watts vs. 65 Lumens I can't /ubbthreads/images/graemlins/frown.gif

Usually, light bulb was advertised as #lumens/watts. I think that is basicly an efficiency issue. Like luxeon 1W is rated at around 20 lumens / watts.

Sid, while you can't convert those ratings directly, once you've been around a bit, you do tend to be able to tell a bit about what you can expect for light output. Kinda sorta, to some extent. It's like if I showed you a picture of a knife, showing blade shape, size, and grind, and told you the blade was 440A, you'd kinda sorta have a feel for performance, right? And ifI told you it was BG-42, you'd have a different feeling.

I'm weak in this area, but even I can get in the ballpark from hearing specs. If you tell me you're running a 5W LS at 5W, and how it's binned, I can take a rough guess at light output. Tell me the optics you're using, and I can guess a bit better about beam pattern. Tell me the batteries (if they're not rechargeable, where my knowledge is completely lacking), and I can kinda sorta guess at runtime. With incandescents, high performance bulbs seem to all put out about the same amount of light, so you can guess at lumens given wattage, though you can't guess at candlepower. Reflectors are tough, I think you have to see their effect by experimenting.

No one is so far ahead of the curve that their batteries or bulbs/LEDs are a quantum leap ahead of everyone else's, so as you see power usage and bulb types from one source, you start to make predictions on others.

Or, maybe I"m completely fooling myself. I'm sure my fellow forumites will let me know in the most humiliating manner if I am /ubbthreads/images/graemlins/smile.gif

Joe

This happens to be a very frequently asked question! Use the search feature and look for Lumen and Candela. If you search under my username for Lumen, you will find several of my posts on threads about Lumen, Candlepower and light measurement; in these threads you will find many useful posts by other authors.

-Jon