Hot, or not?

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trooplewis
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Hot, or not?

I wanted to open a thread in relation to some observations I made in another post.

I ran my Trustfire F20 (one of about 4 look-alike lights, including the Akoray) for 5 minutes on High with a 14500 in it. I picked it up and almost dropped it, it felt so hot. I was actually worried whether I could shut it off without getting burned. So, curious how hot it really was, I went to my garage and got out my I/R Laser Thermometer, a cheapie I got from Harbor Freight for $25 a year or so ago.

Hottest temperature reading I got on the F20 was 106° Hmmmm, that is not really all that hot. I tried my Xeno on high for 5 minutes, it felt REALLY hot, almost unbearable. Measured at 108°, only about 14° above skin temperature.

I shot the 75w lightbulb in my computer room, it measured a high of 186° down to about 150° depending at what point I hit it at. Yes, everyone knows that IS hot, if you have ever tried to unscrew a lit-up lightbulb it is painful. But only to you, obviously not so much to the bulb itself.

So my thinking is that a lot of heat isn't as much as it seems, and probably won't do a lot of damage to the bulb itself, unless the body is NOT getting hot, which is a problem for the emitter. But I bet it can still take a hit of about 190°, which I will soon try to find a way to verify.

 

Thoughts?

Rats, finally sold my 2010 509hp Mustang...now I can buy more lights!

Sold the red one too! Now guess what I drive, doing my penance for 500 hp commuters...

http://dreammustang.com/

http://i884.photobucket.com/albums/ac47/Ha

Edited by: trooplewis on 06/26/2011 - 02:07
trooplewis
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WOW, more interesting stuff.

I pulled the lens out of my SkyRay, and fired up the Thrunite XM-L for about 2 minutes. I aimed the Laser Thermometer into the light (this is not fun, you squint a lot!) and got readings as high as 228° Shazam!

Wonder how much that sucker can take?

BTW, the Thrunite is pulling an even 2.5A at the tail.

Rats, finally sold my 2010 509hp Mustang...now I can buy more lights!

Sold the red one too! Now guess what I drive, doing my penance for 500 hp commuters...

http://dreammustang.com/

http://i884.photobucket.com/albums/ac47/Ha

Langcjl
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I have always, and still do, have a problem with all the speculation that every new high output light will destroy itself with heat. The ever present "it will cook itself". I never see much actual evidence of LED self immolation. I'm not saying it doesn't exist or can't happen, just don't see it. I do know that the UF Manafont dropin can run, tailstanding, for over 35 minutes without any obvious damage. Heat is not good for the efficiency of LEDs for sure but I just don't think that self destruction is assured unless extreme heat mitigation tactics are employed.

Piers said " ....but who wants enough light, when you have the option for far too much "

trooplewis
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The protective circuit on my Trustfire 14500 kicked in before anything bad started happening to the emitter, at least with the F20. Made it start blinking off. Might have been an over-discharge warning.

Rats, finally sold my 2010 509hp Mustang...now I can buy more lights!

Sold the red one too! Now guess what I drive, doing my penance for 500 hp commuters...

http://dreammustang.com/

http://i884.photobucket.com/albums/ac47/Ha

E1320
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I think if it was to hot to hold it was closer to 120f, unless you have really sensitive hands or were not prepared for it. I used to work in a lab and we used to handle hot items that we would measure temps on all the time and we concluded that most people can hold something up to 120f before they let go.

I am already visualizing the duct tape over your mouth.

Langcjl
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trooplewis wrote:

WOW, more interesting stuff.

I pulled the lens out of my SkyRay, and fired up the Thrunite XM-L for about 2 minutes. I aimed the Laser Thermometer into the light (this is not fun, you squint a lot!) and got readings as high as 228° Shazam!

Wonder how much that sucker can take?

BTW, the Thrunite is pulling an even 2.5A at the tail.

228 degrees. Now that's getting hot! 361 degrees is when solder begins to melt according to a quick google search. Does anyone know the actual temp that an LED turns blue and dies?

Piers said " ....but who wants enough light, when you have the option for far too much "

2100
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Thought junction temps can do max of 150 deg C, or 302 deg F.

agenthex
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That's a pretty neat idea. I'm going to try mine on the lights I have.

Reading this makes you smarter: http://lesswrong.com/

Match
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I've seen a couple leds fail in stock lights.  Both were crappy 3aaa headlights with cree xp-c's (I think).  After autopsy I noted that the emitters were mounted on a 20mm star and completely encased in plastic, i.e. nowhere for any heat to go.... Also of note is that the led's didn't fail completely, but were extremely dim.

E1320
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Match wrote:

I've seen a couple leds fail in stock lights.  Both were crappy 3aaa headlights with cree xp-c's (I think).  After autopsy I noted that the emitters were mounted on a 20mm star and completely encased in plastic, i.e. nowhere for any heat to go.... Also of note is that the led's didn't fail completely, but were extremely dim.

That happened to me I had an X-2000 turn on in my jacket pocket for God knows how long and when I finally found it the dome had fallen off the LED and burned itself out.

I am already visualizing the duct tape over your mouth.

brted
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LED's will go blue and then burn the die permanently, turning the die brown. I've seen pictures of LED's that have been burned like that. Sometimes it is only part of the die that turns brown. So they definitely can burn, though I don't know at what temperature.

jamesearljonesi...
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I was using an x2000 in a crawl space for a while then i dropped it. the led came off the star i guess being too hot the solder melted and the jolt knocked it off. of course theres no heatsink under those stars on the x2000 so heat  has no place to go.

03/04/16 

 

8 lives left

trooplewis
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I wonder how accurate my Laser Thermometer is when aimed directly into a 720-lumen emitter, especially with the reflector concentrating the beam. I'm really not sure how valid that kind of reading is, but I'd like to see what others get with theirs.

Rats, finally sold my 2010 509hp Mustang...now I can buy more lights!

Sold the red one too! Now guess what I drive, doing my penance for 500 hp commuters...

http://dreammustang.com/

http://i884.photobucket.com/albums/ac47/Ha

bushytails
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I tested my skyray s-a1 with a new driver the other day, it peaked at 125.8F, measured at the head about where the emitter was, with cooler on either side.

 

"I never see much actual evidence of LED self immolation." - I've seen it twice, both in cheap flood-to-throw lights.  The first was a small sipik, and the golden dragon took on a much less golden color (mostly pure blue) after a few minutes on a fully charged 14500.  The other was a SmallSun 18650 powered, with a real cree emitter, that went from a nice pretty neutral white to bright purple at much less brightness when I tried using it for a battery runtime test.  Taking the light apart showed it had NO heatsinking.  Emitter on a nice star...  not touching any part of the flashlight.  The pill was a hollow tube, with the emitter held in by a plastic clip, pretty much just dangling on the wires, with no thermal path to the body at all, nor any way there could have been one with the design.

I plan on putting a xm-l in said light, but I'm going to have to either turn a new pill (which would require throwing $125 at my lathe for thread cutting gears), or at least make a press-fit copper slug to drive into the hollow pill and get some heat into it...

 

My cheap P7 drop-in seems to overheat quite quickly, as the output brightness drops by about half within 30 seconds, even with batteries I know don't do that.  If I let it cool for a minute, then it'll be bright...  for a little bit again.  Body of the light never gets warm.

--Bushytails

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Ouch!  I just burnt myself on my Trustfire F-25.

I must have dropped my multitool on it in my pocket, and turned it on, but the way my pocket contents were arranged, didn't feel it.  I went to get my multitool back out, and noticed my pocket felt really warm...  then suddenly very hot when the light touched the side of my leg through my pocket.  Figuring this wasn't a good thing, I promptly dropped everything I was working on, and my multitool, and got the flashlight out of my pocket in record time, not sure if it had short-circuited the battery or what.  To my relief, the light was just on, and not in the process of exploding into a lithium-fueled mess, so I turned it off...  and then I promptly dropped it too, as it was really, really fucking hot.  I now have a small blister on my index finger where I touched it nearest the head.

After waiting a few minutes for the light to cool, with it off, it was still barely holdable.

So...  pocket-rockets may be just fine in open air, but insulate them (like inside of clothes), and they can get quite hot indeed.

--Bushytails

trooplewis
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Wish you could have gotten a temp reading on it, curious how hot it got. looks like that light puts out 1.2A max.

Rats, finally sold my 2010 509hp Mustang...now I can buy more lights!

Sold the red one too! Now guess what I drive, doing my penance for 500 hp commuters...

http://dreammustang.com/

http://i884.photobucket.com/albums/ac47/Ha

agedbriar
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I use a dark matte masking tape to bring surface emissivity to the standard 0.95 value my IR gun is set to. Although inexpensive (from DX), using proper technique, the reading off a large pot with boiling water was within a few tenths of a degree Celsius with local heigth accounted for. Amazing!

A flashlight is more challenging, as the strong curvature of the body reduces measurement accuracy.

Don
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Langcjl wrote:
trooplewis wrote:

WOW, more interesting stuff.

I pulled the lens out of my SkyRay, and fired up the Thrunite XM-L for about 2 minutes. I aimed the Laser Thermometer into the light (this is not fun, you squint a lot!) and got readings as high as 228° Shazam!

Wonder how much that sucker can take?

BTW, the Thrunite is pulling an even 2.5A at the tail.

228 degrees. Now that's getting hot! 361 degrees is when solder begins to melt according to a quick google search. Does anyone know the actual temp that an LED turns blue and dies?

 

This is going to vary from manufacturer to manufacturer.

 

The phosphor is usually the first thing to die - hence the blue colour. All white LEDs are blue LEDs with a phosphor coating to approximate white light. It will degrade over time (Exacerbated by heat) anyway - LEDs are reckoned to be dead at about 50% of original output. There is an absolute upper limit - most semiconductors stop working at over 100C or thereabouts. LEDs are semiconductor devices.

What will terminate any LED is melting the bond wires (This will have more to do with excess current than absolute die temperature). The wires are very fine and too much current through them will melt them.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...