White LED appropriate for illumination?
in [Design]
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From: GregS on 15 Feb 2010 09:58 In article <58c8de2d-d513-4b2d-9130-28c4bc047c59(a)e19g2000prn.googlegroups.com>, Rich Grise on Google groups <richardgrise(a)yahoo.com> wrote: >So, I'm going on a camping trip, and I plan to bring along some >reading material for >the time between sundown and the time when I get bored watching the >stars and >listening to the wildlife until I'm tired enough to sleep. > >So, I need some kind of lamp that's handier to operate than an >ordinary flashlight, >but will illuminate a page of print brightly enough to read >"normally." And I specifically >want a white LED (or LEDs), for battery life - that's another problem >with an incandescent >flashlight, even with fresh alkalines, notwithstanding that stupid >spot - I need more of >a flood, so I don't have to keep pointing the light at the passage I'm >reading. > >I've heard tell of LED bike headlights and the like; what I want is >some wide-angle >"flood" light, that could illuminate an ordinary 8 1/2 x 11 page from >about two feet >(2/3M) away, while I'm at a normal reading distance (18-24" (1/2 - >2/3M)), brightly >enough that I don't get eyestrain. > >Does anyone have any recommendations, or need more info? > >Thanks, >Rich Just had the power off for 3 days last week, I was sort of camping. You didn't say what type ofcamping, backpacking ? There is one lamp everyone should have . Its great around the house, camping, garage, etc. Kmart had them for $10. http://scoutmaster.typepad.com/my_weblog/2006/01/innovage_20led_.html
From: GregS on 15 Feb 2010 10:01 In article <hlbn90$jff$2(a)usenet01.srv.cis.pitt.edu>, zekfrivo(a)zekfrivolous.com (GregS) wrote: >In article <58c8de2d-d513-4b2d-9130-28c4bc047c59(a)e19g2000prn.googlegroups.com>, > Rich Grise on Google groups <richardgrise(a)yahoo.com> wrote: >>So, I'm going on a camping trip, and I plan to bring along some >>reading material for >>the time between sundown and the time when I get bored watching the >>stars and >>listening to the wildlife until I'm tired enough to sleep. >> >>So, I need some kind of lamp that's handier to operate than an >>ordinary flashlight, >>but will illuminate a page of print brightly enough to read >>"normally." And I specifically >>want a white LED (or LEDs), for battery life - that's another problem >>with an incandescent >>flashlight, even with fresh alkalines, notwithstanding that stupid >>spot - I need more of >>a flood, so I don't have to keep pointing the light at the passage I'm >>reading. >> >>I've heard tell of LED bike headlights and the like; what I want is >>some wide-angle >>"flood" light, that could illuminate an ordinary 8 1/2 x 11 page from >>about two feet >>(2/3M) away, while I'm at a normal reading distance (18-24" (1/2 - >>2/3M)), brightly >>enough that I don't get eyestrain. >> >>Does anyone have any recommendations, or need more info? >> >>Thanks, >>Rich > >Just had the power off for 3 days last week, I was sort of camping. >You didn't say what type ofcamping, backpacking ? > >There is one lamp everyone should have . Its great around the house, >camping, garage, etc. Kmart had them for $10. > >http://scoutmaster.typepad.com/my_weblog/2006/01/innovage_20led_.html > Yes, its bluish. I do hate that color, especially for camping. I'm still working on making some more Crei warm white lamps for portable use. I got them on around the house, inside and out. greg
From: Paul Keinanen on 15 Feb 2010 13:50 On Mon, 15 Feb 2010 03:43:14 -0800, Robert Baer <robertbaer(a)localnet.com> wrote: > 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). This is very much the situation, when the spectrum can be practically anything. If the spectrum would be linear or even black body shaped, you could calculate it. However, having a light source with some odd spectral distribution and trying to read a text printed of non-black ink on non-white paper would cause quite unreliable results :-).
From: Glen Walpert on 15 Feb 2010 20:45 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
From: Don Klipstein on 15 Feb 2010 21:19
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) |