Overheating LEDs

[scottaw]

So i got 2 lights this week that brought a question to mind. With all these new high power leds overheating and going into protection, dimming, etc.... What about not using a window on the light? I got a CMG ultra-g this week, which is considered by many to be one of the toughest lights on the planet, no window. The arc aaa, the inova x5....all waterproof and tough, why not a rebel-led without a window, wouldn't all the heat just roll off the front? Or am i misunderstanding and it's the electronics that are overheating?

 

[LukeA]

So i got 2 lights this week that brought a question to mind. With all these new high power leds overheating and going into protection, dimming, etc.... What about not using a window on the light? I got a CMG ultra-g this week, which is considered by many to be one of the toughest lights on the planet, no window. The arc aaa, the inova x5....all waterproof and tough, why not a rebel-led without a window, wouldn't all the heat just roll off the front? Or am i misunderstanding and it's the electronics that are overheating?

I would definitely use a window with all Rebel and SSC lights, but only because they both have soft silicone domes. With, say, a Cree, Lux, or other emitter with a hard dome, I think that it would be fine to not use a window.

 

[sORe-EyEz]

i think the window is there to protect the reflector & the LED. a marred reflector gathers less light to throw outward. :thinking:

 

[VidPro]

yes it is true that the window increaes the containment of the led, and therfore the heat.
but at least the light energy escapes the window, and the window is exposed to the outside, allowing it to cool somewhat.
if the window was black, leds do get hotter then the light energy cannot escape the front, and you get more heat.

i munched a bunch of white 5mm leds learning that trick the hard way. i had the project Face down on the leds doing testing, while it turned blue

as for doing that with a flashlight, i refer to the posts above, it would work, but it would be a bigger problem in most situations to not have the lens there.
ok for area lighting. but even with crees, you would want to make sure any cheep coated reflector wasnt destroyed instantally when you get something in there, or when you try and clean it. so a cree or a luxIII AND a metal reflector.

 

[Codeman]

To expand on what others have said...

The majority of heat from LEDs is transmitted through the heat sink and not via IR heat as is true with incandescent bulbs, so I really doubt losing the window would have a big effect, assuming that the heat sink is doing it's job properly. If a heat sink is absent or not transferring heat properly, removing the window would be a drop in the bucket as far as heat goes. Certainly, having air flow around the LED would help, but by how much? It might be interesting to know, but I doubt it would outweigh the benefits that a window does provide.

In most lights, windows serves another function -to protect the LED and reflector. If you've ever tried to clean a good reflector, such as the McR series, it can be difficult, and can easily result in more damage. Plus, going windowless with a SSC LED isn't feasible, as the gummy dome would get filthy in no time.

Not having a window on the UltraG's and Arc AAA makes sense, but I'll stick to lights that have windows most of the time. If properly heat sinked, high-powered LED functions just fine with windows and the windows provide real benefits in regards to LED and reflector protection. Plus they are a simple and effective way to protect against the elements so that user replacments are easily accomplished. If an UltraG or Arc AAA lost it's seal, it would have to go back for repair. If a window or o-ring breaks, those can be fixed by most people without having to send the light in for repair.

 

[legtu]

5mm LEDs(the ones used in ultra-g, x5, etc.) generally doesn't require heatsinking and are pretty much self contained(they already have built-in 'mini'-reflectors and is protected by a clear epoxy dome).

cree/luxeon/ssc/rebel LEDs on the other hand have domes that aren't designed to be out in the environment. majority of the heat produced by these LEDs comes out the back through the slug and not out the front.

 

[scottaw]

See, i learn new things here every day...i was just thinking of the cheaper lights like the rebel-fenix's turbo mode but i guess i just gotta spend more money on better lights with better heatsinking....looks like a Mc is in my future.

 

[yellow]

"Window" :thinking:
You mean the front glass?

That is there primarily to protect the reflector from dust and would make no change at all for loosing heat with a led.
The heat of a led goes into the slug, from there to the heatsink and now - if the light is built good - to the body of the light, where it is spread over a large surface.

The idea of not using a front cover is like "why do airplanes have wings?"

 

[VidPro]

you cant say NO, none whatsoever, that is not true enough. mabey little, but never none.

first lots of lights have aluminum reflectors that whatever air exposure they get , would reduce the heat on the led, because the reflector is in the path for heat from the emitter.

secondly the cree (for example) has a aluminum ring on the top, that conducts lots of heat, and is a point that is, and can be used for heat removal. a well made aluminum reflector passes this heat off of it. that ring . if you pop off the cree ring, you see that it has partly the function of removing heat from the front, it is wrapped around the emitter at the base of it, its not just a side ring.

thirdly all leds, heat escapes out the front of the led, besides the light that escapes out the front which can get converted to heat.

so while the heat sinc is designed to remove the heat, and removes the heat sufficientally, it certannly is not the only location that heat departs the led, just the best.
a cree in an area lighting situation would be much cooler than one stuffed in a light.

 

[Gunner12]

...thirdly all leds, heat escapes out the front of the led, besides the light that escapes out the front which can get converted to heat...

(had a long respond going but the computer spazed and lost it)
I thought LEDs produced light out the front and heat out the back. The only heat conducting thing the LED is connected to is the slug and since it is behind the diode, the heat should come out the back of the LED. You might be able to feel heat when you shine a high power light on your skin because some of the light is absorbed by your skin and is transfered into heat. Most of the heat comes out the back.

The CMG Ultra-G, Inova X5, and Arc AAA use 5mm LEDs which are self contained from scraches and direct contact to the fragile part of the LED. You could break a high power LED like a Seoul, Luxeon or Cree by pressing down on the dome hard enough to break the electrical connection to the diode. You can not do this with a 5mm LED, your finger will break first. The window/lens on high power LED lights is to protect the LED and reflector from any direct pressure and usually has nothing to do with heat from the LED.

 

[VidPro]

Most of the heat comes out the back.

.

right, MOST of it is directed out the back, i am just saying that isnt ALL of it.

what is out the front might be insignificant to nessisary cooling, but it exists therefore it is.

and i did indicate that everything else applies, there is a good reason for the front translucent cap, and most of this stuff needs one, that doesn't prevent someone from reducing the led emitter temps (a tiny bit) by removing it , but i dont see that becomming some usefull trend like no fenders on a Mountain bike .

never say never again

 

[Gunner12]

right, MOST of it is directed out the back, i am just saying that isnt ALL of it....never say never again

You are correct, there is still some heat coming out the front of the light(though so little it is usually insignificant). Never say never, very good advice.

 

[yellow]

ok, a very tiny bit of heat might be possible to get away other than via the slug,
but what gives?
One use without the front glass and the expensive (in case of a Cree) reflector is wasted.

Thats like not mounting brakes to save weight and braking by driving into obstacles.

 

[yaesumofo]

Heat is the enemy.
This is why I asked Don to mod a PD for me with a Seoul emitter.
He made it a mixed mode (the first one) the light runs as bright (brighter)as my older U bin Lux III. It is not being driven to the maximum. It doesn't warm up more than a couple of degrees. On low it runs for days.

So my question is this Why are lights being made which do not utilize this newly found efficiency? It seems to me that instead of going for a cooler longer running light which is still brighter than the older generation of lights. Companies are going for Max output. Max output is all about light and heat generation.

I would like to see more lights made to take advantage of better run times cooler running lights.
You may want to look into modding your new light to reduce the output The light bull run longer and cooler this way.
I have one of the first Cree lights made available from the shop.
We all know they were bright and the did not require the same amount of energy to maintain the amount of light. In that light the choice was to make the light run BRIGHT so they did this without concern for runtime or heat output...Just like many of today's new flashlights.
I go to that light when I want sheer output.

IMHO If a light has a reflector which is by nature a delicate surface it needs a window.
If the reflector is just a polished funnel of aluminum with an emitter at the bottom (ala ARC AAA) then a window is not necessary..unless the emitter is basically a hunk of jello sitting on top of a tint piece of magic semi conductor.
The LUX three is more heavy duty than the Seoul. The Cree is quite well protected compared to a Seoul jello emitter. Not to mention the fact that the Seoul emitters are magnets for dust. It sticks to these emitters. They must be protected by a reflective/window package.

Anyway Seoul emitters (and others) can run cool and still put out a hell of a lot of light. A good reflector is a must.
Today it seems as though the consumer wants OUTPUT. Manufactures are responding to this desire with BRIGHT flashlights which run HOT.
This is called design compromise. As a customer If the heat generated by the light is important to you then add it to the criteria you use when buying a flashlight. Just like output and runtime.
designing a flashlight which is not as bright may not be as popular as the bright version.
BTW My Inova X5 never warms or heats up in any way. I do not believe that these lights were set up as high current blasters. They were bright for their day. I must admit I can't remember the last time I used my white X5. The green one well that is different...
My opinions only your mileage will vary.
Yaesumofo

So i got 2 lights this week that brought a question to mind. With all these new high power leds overheating and going into protection, dimming, etc.... What about not using a window on the light? I got a CMG ultra-g this week, which is considered by many to be one of the toughest lights on the planet, no window. The arc AAA, the inova x5....all waterproof and tough, why not a rebel-led without a window, wouldn't all the heat just roll off the front? Or am i misunderstanding and it's the electronics that are overheating?

 

[NA8]

If you want to know what the temp is on a LED without the window, just look at the reviews that show the run time temperature curve. Usually they remove the lens to make access for the thermocouple wires. The question is usually how much hotter is it with the lens in place ?