Throwing an LED

[techwg]

Ok, What is it about led's that make them not as good at going the distance? Incans seem to cut through, but led seems to lag behind a little. My guess is it must be to go with wavelengths or something because an incan has more diverse light. Either that or its to do with reflection and making the light throw all the light out of the front.

 

[FatTony]

My Streamlight Propoly Lux (with a SSC P4) throws just as well as an incan...

 

[TITAN1833]

My point here is,there are led flashlights that have awesome throw but,Incans seem to cut through fog alot better than led though.And color rendition is better outdoors with Incan's, So IMO get both.

 

[Steve L]

An incadescent radiates light in a 360 degree pattern, so more light hits the reflector and can then be focused for more throw. A LED throws light forward(~70 degree) not as much hitting the reflector. I believe wavelength has more to do with it's ability to better penetrate smoke and fog.

 

[sysadmn]

Part of the answer is the reflector and optics. We have a century spent perfecting lamps, reflectors, and lenses for incandescents. Optics and reflectors custom designed for an LED are relatively new. In addition, we haven't done a lot of tuning on the light distribution from an LED. Most LEDs are still general purpose, with a handful of choices for pattern (at best). Go to the GE, Sylvania, or Cayley website - there are thousands of bulbs to chose from. As more money pours into LED design, these things will improve.

 

[PegAir]

LED's that use glass lenses (search for aspheric) can throw as far as an incan. One other method to overcome the LED's emitter spread would be to use a cassegrain style reflector. I saw a review of one, where the led was at the center of the protective glass and pointed down at the reflector.

As to color, here is an excellent article from an excellent website all about lighting.

http://www.danielsternlighting.com/tech/lights/light_color/light_color.html

 

[Dinan]

This was discussed quite a bit in this thread: http://www.candlepowerforums.com/vb/showthread.php?t=170775

I think the general consensus was the lack of an LED's larger wavelengths (oranges/reds) was the reason it didn't seem to penetrate fog as well as incandescents (smaller wavelengths like blues get scattered more easily).

 

[Ra]

Sorry guyzz,

It has absolutely nothing to do with the emitted spectral range, or fog penetration whatsoever!

It's the surface-brightness: every lightcourse has it's own typical surface-brightness: The amount of light (lumens) emitted from 1 square mm of emitting surface.
Example: A halogen with a filament size of 1 by 4mm with 200 bulblumens output has a surface-brightness of 200/(1*4)= 50lumens per square mm.

A reflector reflects an image of the filament towards infinnity creating the beam, by reflecting the image, it also reflects the surface-brightness. But reflection-losses within the reflective material cause the aparent surface-brightness to be a few % lower compared to the filament itself.

The throw of a light is determined by the surface-brightness of the source (led-die, filament or arc) and the size and reflectivity of the reflector (..And reflector needs to be parabolic..) So when you increase the reflector-diameter, you increase throw. And when you increase the surface-brightness (by overdriving the bulb..) you increase throw.

A few years ago, leds did not reach the surface-brightness of incands! So you needed a much bigger reflector to reach the same throw as with incands.

But the led-technology is the fastest growing technology in our world: The surface-brightness of leds already surpassed normal incands, only the most powerfull halogens stay ahead a few steps (with only 50 hours of burntime) But that will not be for long!

In a few years, led's will surpass incands on the few fields on which incands still are preferred above led's now

Just wait for it...



Regards,

Ra.

 

[techwg]

Ra, that was the most enlightening post i think i have read, thanks alot for that. See it makes sence to me now,its not really as such a mystical thing about the lack of throw.

I have actually not been impressed by my Surefire P61 incan. It is ok, and has nice medium range throw, but i live on a small L shaped street, and im on the corner. My P61 just about reaches the other side iof the street with about a big enough beam dispursion to light up a truck, but with the brightness enough to see if a white poll was there and thats about it. So my hope is that i will get an LED light that has a beam that does not fizzle out so much and give me powerful beam so i can see detail at a distance.

Ra, if someone took a Q5 180 lumen led, and had a good reflector etc, you think theres no question it would totally oblitorate my P61 incan surefire? Im hoping so.

 

[2xTrinity]

The most significant factors is the optics -- as already mentioned n most LEDs available today, a small percentage of the light is collimated into the hotspot, and a large percentage exits as spill. In fog, it causes a situation where one is trying to view a target that isn't receiving a lot of light/lux, through a veil of fog that is very brightly lit from the excessive spill. When comparing lights with simialr lumen output and beam pattern (an aspheric LED of mine, to a stock maglite with xenon bulb for example), where the only significant difference is the color, the lights are fairly close to each other in performance.

The preponderance of blue light is another valid issue, shorter wavelengths scatter more, and generally isn't very useful outdoors in terms of providing visible contrast: incandescents greatly exaggerate reddish shades compared to natural light, thus I dislike them for in-home use, but when trying to identify something with a small amount of light, as with a flashlight outdoors, contrast is more important than color accuracy.

 

[bones_708]

Pelican has a design than puts the emitter in the center of the lens shooting back at the reflector. Recoil is their name for the lights using this technique. It produces a beam with a very tight focus and long throw, like most pelican lights, and is reported to be good at cutting thru smoke and fog unlike most LED's.

 

[sORe-EyEz]

yap, some Pelican lights have the recoil technology. but i wonder if the circuit draws heat away from the bulb away effectively & not forgetting the (ploycarb?) stem that holds the bulb in place- is it potentially weaker than those placed at the base of reflectors...

jus some doubts i have of the recoil series... :thinking:

 

[Patriot]

Ra, that was the most enlightening post i think i have read, thanks alot for that. quote]

Ra has a habit of doing that around here :thumbsup:

 

[techwg]

I think led flashlight companies need to look into making their lights perform like incans, for throw and illumination. Yes the spectrum is not the same, but if they focus it properly, we will have something that will reach out and touch someone.

 

[Ra]

Indeed the penetration of haze and fog depends on the emitted spectrum and sidespill.

Each type of lightsource needs it's own design collimator or reflector. Tho most lightsources (incands and HID) work well with a conventional parabolic reflector, led-emitters like Luxeon, Cree and Seoul do not..

The best collimator for those emitters is the TIR (Total Internal Reflection..) optic: Grabbing the lumens-output over a 150-170 degree angle, making the TIR-optic the most efficient colimator today, converting +90% of the led-lumens into torch-lumens! The problem is that they only are aviable in a few sizes: small and smaller.

An aspherical lens is a good solution to create a narrow beam, but is not very efficient: Grabbing only about 80 degrees of emitted light, positive: it grabbes the light where it is emitted most: at the front of the led, something the conventional reflectors cannot do.

So why do aspherical lenses throw so well?? Because they are aviable with larger diameters then TIR-optics. A TIR-optic with the same diameter would give the same throw, but will also give more sidespill: The extra lumens the TIR-optic collects go into the sidespill

The Cree Q5 definitely is one of the best solutions to surpass even the best halogens on surface-brightness. And with the much more lumens, you'll have decent sidespill too..


Regards,

Ra.

 

[TITAN1833]

Ra,does the efficiency increase,if the aspheric is coated.:thinking:

 

[techwg]

If you have a Q5 light with an aspherical lense, do you loose all spill? i would not want to lock out all spill, its not safe for security reasins someone could be hiding in your new blind spot and unless you happen to scan across them you would not see someone charging you.

 

[Ra]

Ra,does the efficiency increase,if the aspheric is coated.:thinking:

Yep: Any air-to-glass or glass-to-air surface means a loss of a few % (4% average) An anti reflexion coating reduces that loss. With high efficiency coatings you gain up to 7% of light-output.

And Techwg: The Cree propably is the best emitter to use with aspherical optics: The design of the Cree is somewhat different compared to the Seoul or luxeon, the lens on the Cree already slightly colimates the light into a 140 degree angle (give or take..), so more of the lumens-output will be grabbed by an aspherical lens.

With an aspherical lens, it's hard (..with a high quality lens impossible!!) to obtain a beampattern with both throw and sidespill. It's one or the other: You must place the lens out of focus to obtain a wider beam for sidespill, but that will not create a bright center for throw. For throw, the led-die must be exactly placed at the focalpoint of the lens, but virtually no sidespill will be the result.

So if you want both sidespill and throw, you'll have to be able to focus the lens, but you can't have both at the same time. Maybe you'll be satisfied with a focus-position somewhere inbetween...


Regards,

Ra.

 

[techwg]

i now just need to find the perfect throwing led, i have a Surefire C2 HA-III on its way, here is a link to a satalite pic of my area and overload with distances of my P3D test and if they were good or not. Im hoping to reach 60m with good detail at some point even perhaps with the C2, i sont know.http://img206.imageshack.us/img206/6128/techwgturfhf4.jpg

Any ideas of something average priced that may fit the bill unless you think the C2 will do.

 

[nutz_about_lights]

Yup as the others said its due to the different wavelengths between LED and incans. I read somewhere that incans are better to use in the woods at night, cause they offer more ''natural'' light the LEDs, which produce a sort of characteristic blueish tint.