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?
I don't know what's available where you are, but over here in India, there's plenty to choose from, mostly Indian and Chinese products. Too numerous to describe. Some have a dozen LEDs in a small table lamp type frame using AA cells at under $1 US. Some have 200+ LEDs in a 360-degree lantern type configuration with a built-in rechargeable battery for ~$50. Some come as direct replacements for mains incandescent bulbs with 10-100 LEDs, but run from rechargeable batteries in emergency light mode (~$3-10). Some have remote controls. Most of the ones I've seen except the flashlight types will meet the lighting angle you need. These are just a few examples of what we get here. I'd think'd be available almost everywhere else.
These were on sale in the local HF store for 3.99 last week. Mine works well although it is aimed too high when on my head. I haven't used it long enough to tell how long the batteries last.
One of the headband mounted lights with a diffuser ought to do the trick. You might find it worthwhile bridging the switch with a 470k resistor so you can find the thing in total darkness too.
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.
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. :-)
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.
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:
formatting link
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.
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
The OP was asking for a light to be used from 2 feet away. What fluorescent are you talking about - the 6 watt F6T5? (6 watts, 295 initial lumens, 230 design lumens)
The F4T5? (4 watts, 135 initial lumens, 95 design lumens, and light emitting portion of the length about 3-3.5 inches long) A 3.5 inch line source from 2 feet away will have nearly as much of the shading you mention as a point source will.
I tried web searching for that one, and can't find it. Are you sure it's not an L 8 W /640? (Apparently equivalent or nearly equivalent to F8T5/CW)
I can believe 250 lumens from underpowering that lamp at 5 watts.
(I just checked my Philips catalog just now - F8T5/CW at 8 watts produces 400 lumens initial, 300 design. The L 8 W /640 achieves 385 initial lumens with 8 watts.)
A 250 lumen line source, over a 100% reflective planar reflector, produces 50.7 candela, good for 136 lux at 2 feet.
A lambertan emitter with no optics at all achieves that illumination with 159 lumens, maybe 180 considering that style LED often has radiation pattern a little less directional than lambertian. Two of those Seoul Semiconductor W42180-U1 will achieve 180 lumens at about 1.1 watts apiece.
The efficiency of inexpensive and easy driver circuits for fluorescents and for LEDs powered from batteries is another reason why I would go with LED.
I have it very often in use to illuminate my keyboard, when the room light is dimmed. It is in a camping light and works from 6 NiCad D-cells. So the batteries are kept alive by frequent use. I like it because the long tube doesn't make shadows and I often have to look up something in books. My distance is around 30 cms only. I also have a flashlight with a 3W LED, but it is too blueish and the reflection from the paper blinds my eyes. The /540 is right, maybe an older model, bought it almost 8years ago. cool white is written on it as well. ciao Ban
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