What is it about LCD flash lights that make me not like them..

I mean from the boxes they seem better in everyway. Last longer, are brighter, use less batteries, but why does it seem that they do not shine as “far” as the other ones. Isn’t brightness the same as the distance light can travel? Maybe this should go under IMHO not sure, mod please move if this is not a GQ.

I assume you mean LED (light emitting diode)? LCD is liquid crystal display.

Usually it’s because LED flashlights have poor optics. The light is spread out over a wide area instead of being focused into a tight spot.

This is especially true of flashlights that use contain several LEDs; there’s not enough space to put a decent size reflector around each LED. Sometimes there’s no reflector at all, and the only “optics” is the curved front surface of the LED itself. Unfortunately this configuration is very common because five 0.2-watt LEDs cost much less than a single 1-watt LED.

Also, LEDs emit a more white (blue) light, so it may appear brighter than it really is.

But there are some LED flashlights that combine a single high-power LED with a decent size reflector. Flashlights with 1-watt Luxeon LEDs are pretty good, 3-watt is even better. And I understand Cree LEDs (like this) are better still.

Although they appear white, there are different ways to make the eye perceive white light - you can add together a little of many different visible wavelengths - which is pretty much what you get with daylight, slightly less so with incandescent filament lamps, but there’s still quite a spread of wavelengths in the mix.

Or you can just add together a smaller number of somewhat narrower bands of wavelengths from opposite (ish) ends of the scale - and the eye will still perceive it as white, because the receptors in your eye are still stimulated by it.

But… although those ‘white’ lights appear similar when directly viewed by the eye, they don’t all reflect back off things in the same way - in the case of white LEDs, they’re usually a blue or purple LED with a yellow phosphor on them - so that the light they emit is a mixture of the yellow emitted by the phosphor when it absorbs and is excited by some of the blue light, plus some blue/purple that leaks through the phosphor unchanged. This means the emission graph not only dips off quite sharply outside the extremes, but it also dips right in the middle - around the 500nm wavelength.

500nm happens to be green, so anything that is fairly pure green in colour (and there’s a fair bit of this on the planet) upon which a ‘white’ LED (based on the above described blue with yellow phosphor) shines, is likely to appear poorly illuminated, even though the light source itself might seem bright.

I have a replacement LED “bulb” for my 3-D cell Maglite. It’s way better than the normal incandescent Maglite.

The way LED lights do “white” is by using a blue LED with an attached phosphor. The resulting color is bluer than the pleasing yellow glow you get from an incandescent source, like an ordinary flashlight, or a halogen bulb in a flashlight. As is the case with fluorescent lamps, even with added fluorescent sources, the color balance is wrong. So it doesn;'t look right, and things illuminated with it don’t look right.

(And the phosphor tends to degrade with age, so as it gets older the light gets even bluer.)

On the other hand, LEDs have lifetimes of typically 100,000 hours, way longer than regular bulbs or halogen bulbs. They’re MUCH “cooler” than regular bulbs, too, not wasting any energy sending photons i n the infrared, where you;can’t even see them anywway. So the LED lights use a lot less energy, last longer, and don’t get hot. But they do look a bit weird.

I agree, mine throws a beam that lights up the yard on a dark night.

Some of the leds make me sick when I view them. It’s probably the wavelength and frequency of interruptions with ac powered leds that do this. They now have a weapon based on led light, that will make people sick. This doesn’t come as a surprise to me since some lights already do this for me. I can’t watch fast movement any more without the same problem. I aged into being this way. Other people on this board have mentioned the same problem with led lights. Some flouresent lights do the same thing for me. Halogen and incandescent lights never cause me problems.

Incandescent flashlight bulbs emit their light from a filament small enough that it’s nearly a point source. Place this in the focus of a parabolic reflector and you get a pretty good long range beam of light. When the light source is more extended it’s harder to focus. The very best LEDs have enough luminosity to match incandescent filaments in performance but many LED flashlights use the cheaper ones and it shows.

Some LED flashlights use pulse width modulation (pwm) to control the brightness of the LED & conserve energy. This is essentially using a little circuit to turn the LED on and off very quickly. Since LEDs don’t have a particularly wide range of useable brightness, you can’t really control the amount of light coming out of them just by sending them lower voltage like you would to an incandescent, you have to flicker them and by changing the durations of the on/off cycle you can change the apparent brightness to the human eye. This also saves battery power, as you’re only actually powering the light for the on duration, and not the whole time.

If the flashlight has multiple brightness settings it probably has a tiny pwm controller built into it. If it takes three AAA or AA batteries, it probably just uses a resistor. There are some electronically current limited ones, but those seem to be rare and expensive (read: Surefire tactical lights).

I had a Petzl Tikka that did this, and it would give me motion sickness if I tried to use it to read at night, even when sitting down not moving. Then again, monitors with a 60hz refresh rate also make me sick, and I’m not too fond of fluorescent lights either.

I don’t understand the point of this post. LED sources are much smaller than incandescent filaments, and much more closelt resemble point sources. They also have a connecting wrire right in front of that junction, but that won;t affect the areas not blocked. My LED flashlights do a pretty goos job of making a collimated beam.

I have 3 watt LED’s in my Mag Lites and they are better IMO as Boewulff said. I also have a ‘Brinkman’ that is 3 watts and about 5 inches long that is my night ‘dillo in the yard’ shooting light. No beam adjust so it spreads more but works good for moving critters and I can hold it with my forearm hand with a rifle or equally well with a pistol.

YMMV

My limited experience with LED flashlights is that they usually have an array of LEDs that is much larger than the ~1mm filament of an incandescent bulb. From descriptions upthread I would presume the better LEDs have small, single, high-intensity emitters; I just haven’t seen one personally. The cheaper LED flashlights do a poor job of collimating the beam, which is pretty much what scr4 said.

Actually LEDs have a huge range of usable brightness, far larger than incandescent bulbs. When you apply lower voltage to an incandescent bulb, the efficiency drops off rapidly because the filament operates at a lower temperature. If you run the bulb at half power, it’s less than 1/2 of full brightness. Try to run it at 1/100 power and it won’t even light up at all. But an LED at half power will be 1/2 of full brightness. You can run it at 1/1000 power and it’d be 1/1000 as bright (i.e. equally efficient).

PWM is used because it’s the most efficient way to extract low power from a DC voltage source. If you use a variable resistor, the resistor uses up a lot of energy. Same with a linear regulator - it just acts like an automatic variable resistor. PWM is basically a rapidly acting switch, there’s very little loss when the lamp is on.

And PWM is used for light bulbs as well, when you want variable power from a DC power source. It’s not very common because, as I said, light bulbs are inefficient at less than full power. (Efficiency depends on filament temperature, which depends on average power, so it doesn’t matter how you control the brightness, it’ll be less efficient if it looks dimmer.) This bicycle headlight is one example. Click on “burn time” and you’ll see that when running at 46% power, its brightness drops down to 30%.

Is that true of the newer generation of LEDs that includes blue(and white), violet, blue-green, pure green, etc? - I thought they just stopped emitting below a threshold voltage.

Most of the LED flashlights I’ve seen have a single LED, which has a single small area of emission that;s much smaller than a filament. I have one that has three LEDs, but each has its own reflector. I’ve never seen an LED flashlight such as you describe. And I’ve seen a lot of LED flashlights.

Pretty much all LED headlamps I’ve seen and used have multiple LEDs in a line or array.
http://en.petzl.com/petzl/LampesNews?News=182
They aren’t as bright as an incandescent bulb, but the battery life and light weight more then compensate.

For individual bulbs the leds have a smaller source for the light. Stop saying they can’t be focused because you decide to compare a single incandescent bulb to a bunch of leds. Leds are manufactured in a plastic case that does direct more light straight ahead. It doesn’t do it as well as a mirrored reflector.

The sign, auto and flashlight manufacturers can focus the led light better than they do. They haven’t had the incentive. They have just added more leds to give off more light, because they still have the mindset that since they use so much less energy they can just whip in a few extra leds. They don’t replace a symbol traffic sign with a led light source covered by a panel with the symbol. They make the shape of the symbol out of leds and turn them on. These are also the signs that give me headaches over time.

This really explains a lot with regard to my dislike of these types of headlamps when I’m using them in the woods.

I’m a hunter. I go into, and come out of the woods after dark. Not “at sunset,” but rather a good 30-60 minutes later… when it’s dark dark. The LED headlamps are great in that they are usually good for an entire season on one set of batteries, but as the world is green, you just don’t get a lot of “bounce back” from the lamp. Makes it tough, and my favorite was a lamp that had the LEDs, but also a large center incandesant lamp with reflector in the middle for a true ‘spot.’ It was bigger, but certainly better. The cheap ass switch broke though, so that one went to the bin.

There is a threshold voltage, yes. But you can run it at an extremely low current.

The LED is a semiconductor so it doesn’t follow Ohm’s Law. It starts conducting (and emitting light) only above a certain voltage. But if you control the voltage to be just a tiny bit above that threshold, you can make it conduct an arbitrarily small amount of current (and therefore consume arbitrarily small amount of power). This is easy to do if you use a current regulator.

I still think this is mostly due to the poor optics on those LED lamps. And the low power of the LEDs themselves. If the batteries last an entire season, it can’t be using much power.

Have you tried something like the Princeton Tec Apex? This has a 3-watt LED in the center, surrounded by a big reflector. The batteries only last 3 hours or so at the maximum setting (I think the “140 hours” refers to the lowest setting), but it’s quite bright. I have one strapped to my bicycle helmet and use it as my primary light. It’s not cheap though, I think I paid about $70 for mine.

Well, it’s only used for about 10 minutes at a time. Just long enough to walk in, and quickly set up. And I tend to use the least power setting required for the available light.