As a sort of running gag in my family, the latest generation (myself included) has recieved at least one flashlight every Christmas. Two years ago, I got a very nice white-LED flashlight whose batteries I have not yet needed to replace. I have many other flashlights of the incandescent variety. Now, here’s the thing: LEDs seem to be very good at blinding people, but not very good at providing illumination. An incandescent bulb flashlight which is much easier to look at also makes a path much more visible. It’s very strange.
I’m sure that it’s a white LED setup, not a blue one, because in an otherwise pitch-black room, turning on the flashlight reveals objects of all colors. I’ve got several incandescent torches with adjustable lenses, so I’m sure it’s not width of the beam that makes a path more visible.
BTW, I mean by a path an outdoor situation - New England mixed forests are my experience, and my LED flash does nothing for me.
Has anyone else noticed this, and if so, can anyone guess why it is this way?
Light output is measured in lumens. Your incandescent bulb throws off a lot more lumens than most LED’s can, at the expense of decreased bulb life, decreased battery life, and increased chances of breakage. Your LED flashlight probably has about 16-20 LED’s, which don’t have the oomph of a regular bulb.
WAG begins here:
LED’s might be more blinding because of the frequencies of light they emit, which your eyes could be more sensitive to. Theory 2 - incandescent = 1 source of light. LED flashlight = many sources of light = increased irritation.
Incandescent bulb flashlights usually have large focusers, produces a narrow beam. If the flashlight is pointed directly at your eye(s), I bet it looks a lot brighter than your LED. But if the beam is even a little bit off, it doesn’t look very bright.
An LED usually has a molded plastic case that acts as a crude lens, producing a broad beam. It looks pretty bright from any angle, but the illumination pattern doesn’t have a well-defined central spot.
There are exceptions, of course. For example Luxeon makes “side emitting” LEDs which are designed to be used with large reflectors to produce a narrow beam.
This isn’t any sort of a rigorous scientific study, but hey.
My interpretation: It’s not how wide you make the beam, but how narrow you make it, concentrating all those photons straight ahead of you, that makes the difference, and from the looks of it, you can’t control the focus on LED flashlights.
Firstly, white LED’s aren’t really white–they are a larger blue LED with a smaller red LED attached, and cross-driven. So there is no green component to the light at all. So if you try to look at green things, they won’t show up well, because they won’t reflect either the red or the blue light well.
Secondly, the short version of the explanation is simply that no LED’s can put out nearly as much light as a lightbulb of the same external size can. LED’s have low minimum power requirements, long lifetimes and have very high efficiencies at low power levels, but quickly fall off at higher outputs because they heat up at a rate faster than they put out more light. Because of this, most all white-LED lights you will find use a circuit to pulse a higher-than-rated voltage to them, to increase the apparent brightness. This pulsing can cause additional problems in use however.
I have a Brinkman led flashlight (the one that Wal-Mart sells), I agree with you in that the two AA batteries seem to last forever. I replace them every few months just because I don’t want them to leak inside and make a mess when I leave the flashlight on a car seat or wherever, but I have never “run the batteries down” in that thing. It’s not water-proof, but I have seen that it is very water-resistant, and priced at $10, it’s practically disposeable anyway. A Mini-Maglight that also uses 2-AA batteries and a krypton bulb puts out a much better quality of light, but can only run a few hours at most. Different colors of LED’s run at different voltages and currents, but for comparision’s sake, a LED flashlight will usually operate 10-20 times as long as a regular bulb flashlight would with the same batteries.
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I have been playing with LED’s and flashlights lately to try to find a cheap IR illuminator that will work with Russian night-vision viewers. It’d be interesting now that you mention it to make a flashlight with one red, green and blue LED just to see how much better it looked…? Hmmm…
I wonder if it’s the same as HID headlights, which also give out a blueish light, they have been accused in blinding oncomming drivers (and they are suppose to be a safty option :rolleyes: ). Something about blue light might cause night blindness at a lower light output.
No green component, DougC? That explains neatly why forest paths of browns and greens are difficult to navigate.
Mayhap there’s an LED torch sold with many small-output LEDs of red, blue, and green.
I thank some of the rest for thoughts on width of beams, but as I said, the lenses on my Maglites are adjustable to create different varieties of beams. I made all comparisons with the beams set quite similarly.
I know there are such devices, but in most cases, I think white LEDs are actually a blue or UV LED chip driving a yellow or white phosphor - your point about spectral deficiencies may still apply though.
Yes, they’re a narrow band blue LED chip with either a yellow LED or yellow phosphor on top. The yellow band is actually pretty wide, but the light output is still somewhat lacking in blue-green and longer red wavelengths, so reds and greens tend to look dull and yellowish under this type of illumination. It is a similar effect to the color distortion of certain fluorescent lamps.
Argh!!! Yes, it is yellow on blue. But anyway, the full-color-spectrum of a regular light bulb is definitely not present. http://ledmuseum.home.att.net/reserved.htm#q11
Another page says to achieve proper white balance of three “RGB” LED’s at a fairly low color temperature, the proportions are typically 60% red, 30% green and 5% blue. At higher temps, the % of red and green go up and the blue goes down.
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An electrician friend of mine, once when repairing a long string of outdoor coloured party lights, tested the bulbs and sorted them into ‘Light bulbs’ and ‘Dark bulbs’.
Those cars are freaking annoying.