<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Doug S:
Actually, Hotfoot, carl is quite right about this. A careful reading of the datasheet shows that the 120 lumen typical is at a junction temperature of 20 C. I have noticed that many here on this board seem to be missing this point. I have been thinking about making a post about the difference in the Nichia and Lumiled methods of rating outputs. Since it is of more general interest, I will start a new thread on the topic.<HR></BLOCKQUOTE>
Doug S,
Good point made on reminding us about the somewhat optimistic figures on the datasheets. But Carl is still quite wrong (sorry Carl).
While I won't disagree with you on your reading and understanding of the datasheets, I'd certainly still have to maintain the incorrectness of Carl's assertion that we're not likely to see a 120-lumen 5W driven to spec.
Carl's post mentioned 120lumen *only* being possible a temp of -20C, not +20C (as the datasheets say) - and suggested below-freezing temps before we could see the advertised performance. The datasheets, on the other hand, do clearly state (as you have pointed out) that the LSs *will* deliver a typical of 120 lumens when driven to spec(electrically) at +20C. All things being equal, the same standards are applied to the 1W, so relatively speaking here, we are all taking apples and apples.
What I will have to concede is that while a 5W may start off at 120lumens or so, this figure may steadily decline as the junction temp rises. I had a breakfast meeting with the chief Lumileds rep in my region (AsiaPac) and he reaffirmed that the datasheets only reflect an average of the luxeons that you get. Output and consumption/drive characteristics *will* vary from specimen to specimen. One other CPF member has actually tested an example of the 5W LS driven to spec and clocked in 130lumens!
I'm not "defending" Lumileds, but manufacturers simply post their typical findings at given repeatable ideal test conditions (which in most cases, do not mirror real-world ideals), but this is beside the point. Is +20C impossible? No. Impractical? Perhaps, for some apps (like flashlights). But certainly possible in freezing ambient temps like winter. Nothing here to suggest that Lumileds was indicating unrealistic or unattainable performance.
At the end of the day, that's all good and fine on paper for the moment, but until we can actually hook one up and measure one for ourselves in *our* respective real world conditions, the utility and mileage we get out of the 5W can only be based on the datasheet.
On a last note, I've seen and messed about with that 3xCR123 5W Luxeon flashlight that Luxeon reps carry around with them and I *can* tell you that this thing will still utterly shred an E2 for output