White LED appropriate for illumination?
in [Design]
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From: Martin Brown on 12 Feb 2010 04:05 linnix wrote: > On Feb 11, 2:49 pm, Martin Brown <|||newspam...(a)nezumi.demon.co.uk> > wrote: >> One of the headband mounted lights with a diffuser ought to do the >> trick. > > I prefer to mount it on my chest. It creates a more even lighting as > well. I use it for home camping, when my companion is asleep. > >> You might find it worthwhile bridging the switch with a 470k >> resistor so you can find the thing in total darkness too. > > Good idea, but I think a smaller resistor would be better. Even 47k > can last a very long time. 470k with these modern high efficiency white LEDs will still put enough light out to see by when fully dark adapted. All you really want to be able to do is get to it in total darkness for instance during a power cut. Being able to trade longevity for brightness might be useful in a real emergency situation. I fail to see why there are not more LED based torches exploiting this nice feature of highly efficient white LED emitters. There are a few around made of doped strontium aluminate luminous plastic. Regards, Martin Brown
From: Rich Grise on Google groups on 12 Feb 2010 16:03 Gack! Once again, too many responses to reply individually and thank everyone - well, I could, but I think everybody knows I'm the laziest man on the planet. That HF unit for 5.99 looks like the one I'll opt for, if I can find a similar one in a physical store where I don't have to go through figuring out how to get it shipped to these boonies. Anyway, I have a lot better idea of what's available, and again, thanks to everyone. :-) Cheers! Rich
From: Bit Farmer on 12 Feb 2010 16:33 Rich Grise on Google groups 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 Rich Go to REI. They have a ton of LED headlamps with a variety of beams. They are a bit pricey, but IMHO are worth it. They are designed to be head mounted and have many models that are quite light. Weight is important, especially when it is on your head. I have used these for reading on river trips for years and they are great. b. Farmer
From: Don Klipstein on 13 Feb 2010 01:29 In article <hl1sko$t13$1(a)news.eternal-september.org>, Ban wrote: > <SNIP previously quoted material> >There are these flourescent small tubes 5W for camping use, they are more >bright and need less power than LEDs and cost less. Easily obtainable LEDs costing not that much more are more efficient than lower wattage linear fluorescents. As in producing at least as much light with 2W as a small linear fluorescent does with 4-5 watts. With even a lambertian radiation pattern LED being more directional than a fluorescent in front of a mirror, and without optics loss in making a fluorescent directional, and the LED gaining efficiency as input power is reduced (if only moderately or moderately severely), I would expect at least as much ability to iluminate a page of paper with 1.25-1.5 watts of LED power as I would expect from 4-5 watts of fluorescent power using a small linear fluorescent lamp. For example, in stock at Digi-Key for $6.04 USD each plus shipping in quantities of 1, plus requirement to meet a fairly small minimum order or pay a somewhat minor handling fee: W42180-U1 Typically 95.5 lumens at .35 amp with typical voltage drop of 3.25 volts. Epoxying it to a heatsink having at least 1.5 square inches exposed other than fin surfaces facing nearby fin surfaces should keep it comfortably cool and cool enough to achieve good chance of producing at least 85 lumens at 350 mA, in any heatsink operating position. The datasheet is at: The W42180 datasheet link in: http://www.acriche.com/en/product/prd/zpowerLEDp4.asp U rank is supposed to achieve minimum 91 typically 100 lumens at 350 mA with heatsinkable surface of the "LED emitter" (what gets attached to a heatsink or a "star board") at 25 C. At this point, I like to see a bucking switching current regulator supplying 300 mA, with typical LED power consumption .96 to maybe .98 watt, and power consumption of the LED and regulator circuit combined maybe 1.2 watt, likely producing a goodly 80 lumens. Four alkaline AA cells in series should power this successfully for 6-7 hours, possibly 8 hours. 80 lumens, even if radiated in a manner very slightly less directional than lambertian, is good for 60-67 lux at 2 feet. I would prefer a few hundred lux - fair chance reasonably obtainable by experimenting with convex lenses, especially ones with lower f ratio. - Don Klipstein (don(a)misty.com)
From: Ban on 13 Feb 2010 02:10
"Don Klipstein" <don(a)manx.misty.com> schrieb im Newsbeitrag news:slrnhnchm9.588.don(a)manx.misty.com... > In article <hl1sko$t13$1(a)news.eternal-september.org>, Ban wrote: >> > > <SNIP previously quoted material> > >>There are these flourescent small tubes 5W for camping use, they are more >>bright and need less power than LEDs and cost less. > > Easily obtainable LEDs costing not that much more are more efficient > than lower wattage linear fluorescents. As in producing at least as much > light with 2W as a small linear fluorescent does with 4-5 watts. > > With even a lambertian radiation pattern LED being more directional > than a fluorescent in front of a mirror, and without optics loss in making > a fluorescent directional, and the LED gaining efficiency as input power > is reduced (if only moderately or moderately severely), I would expect > at least as much ability to iluminate a page of paper with 1.25-1.5 watts > of LED power as I would expect from 4-5 watts of fluorescent power using a > small linear fluorescent lamp. > > For example, in stock at Digi-Key for $6.04 USD each plus shipping in > quantities of 1, plus requirement to meet a fairly small minimum order or > pay a somewhat minor handling fee: W42180-U1 > > Typically 95.5 lumens at .35 amp with typical voltage drop of 3.25 > volts. Epoxying it to a heatsink having at least 1.5 square inches > exposed other than fin surfaces facing nearby fin surfaces should keep it > comfortably cool and cool enough to achieve good chance of producing at > least 85 lumens at 350 mA, in any heatsink operating position. > > The datasheet is at: The W42180 datasheet link in: > > http://www.acriche.com/en/product/prd/zpowerLEDp4.asp > > U rank is supposed to achieve minimum 91 typically 100 lumens at 350 > mA with heatsinkable surface of the "LED emitter" (what gets attached to > a heatsink or a "star board") at 25 C. > > At this point, I like to see a bucking switching current regulator > supplying 300 mA, with typical LED power consumption .96 to maybe .98 > watt, and power consumption of the LED and regulator circuit combined > maybe 1.2 watt, likely producing a goodly 80 lumens. Four alkaline AA > cells in series should power this successfully for 6-7 hours, possibly 8 > hours. > > 80 lumens, even if radiated in a manner very slightly less directional > than lambertian, is good for 60-67 lux at 2 feet. > > I would prefer a few hundred lux - fair chance reasonably obtainable by > experimenting with convex lenses, especially ones with lower f ratio. > > - Don Klipstein (don(a)misty.com) The tube I suggested puts out 250lm and apart from that is a line source which doesn't get shielded that easily as a point source. Makes a difference when turning the pages, with a LED, where yuo have to press down the paper to avoid those ugly shades. So basically you would need two of your LEDs to have a similar illumination. ciao Ban |