White LED appropriate for illumination?
in [Design]
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From: Robert Baer on 16 Feb 2010 04:39 Glen Walpert wrote: > On Mon, 15 Feb 2010 03:43:14 -0800, Robert Baer wrote: > > <clip> > >> Ghaa..lumens, candela, lux, candlepower, percent efficiency, and who >> knows what else (watts per steradian?)! >> Seems every maker uses a different "standard" not only for different >> LEDs they make, but also different than other makers. >> What are the relationships and the conversions? My basic questions >> concerning a given LED would be how bright is it - >> can i depend on the number given to tell one is brighter than another at >> the same drive (seems the answer is NO). > > The answer is 42. Err, make that: > > <http://www.optics.arizona.edu/Palmer/rpfaq/rpfaq.pdf> > <http://www.optics.arizona.edu/Palmer/rpfaq/rpfaq.htm> > > This is the most clear and unambiguous measurement of light primer in > existence, with excellent references for more info. IMNSHO. > > Regards, > Glen > SUPER!! Straight-forward, feet on the ground source! Thank you VERY much!
From: Robert Baer on 16 Feb 2010 04:45
Don Klipstein wrote: > In <AMednZFqgeF3r-TWnZ2dnUVZ_jqdnZ2d(a)posted.localnet>, Robert Baer wrote: >> Don Klipstein wrote: > > (What I wrote including quotation of previously quoted material) > >> Ghaa..lumens, candela, lux, candlepower, percent efficiency, and who >> knows what else (watts per steradian?)! >> Seems every maker uses a different "standard" not only for different >> LEDs they make, but also different than other makers. >> What are the relationships and the conversions? >> My basic questions concerning a given LED would be how bright is it - >> can i depend on the number given to tell one is brighter than another at >> the same drive (seems the answer is NO). > > LEDs rated 1 watt or more are normally rated in lumens at specific drive > current, often either 350 mA or more than one drive current including 350 > mA. > > Most LEDs with maximum current 50 mA or less are rated in millicandela > or candela at a specified drive current, usually 20 mA. A candela is a > lumen per steradian. > (The lumen is defined in terms of the candela and steradian, rather than > a candela being defined as 1 lumen per steradian, but I digress.) > > My experience suggests that many LEDs with maximum current 40 to 300 mA > have the manufacturer stating both candela/millicandela and lumens. > > In my experience, most LEDs in Digi-Key's online catalog have both > figures listed. It appears to me that if the manufacturer supplies one > and not the other along with a nominal beam width, then the other is > obtained using an equation that oversimplifies by assuming the beam is > uniform and 100% of the light is in the beam - usually not far off for > most LEDs rated *honestly* for beam width and beam width at least 30 > degrees. > > As for what a lux is: That is candela divided by square of distance in > meters. > > - Don Klipstein (don(a)misty.com) What got me started with the complaint, was seeing a listing from one maker that used almost every one of the "units" i mentioned, and the straw that broke this camel's back was percent efficiency (and who in the h*ll knows what that is _supposed_ to mean)! |