Is a hot LSH a problem?

[Sakugenken]

Sorry if this is a stupid question but... I keep my LSHFP in my car (it fits perfectly in the ashtray--I'm a non-smoker). It is summer now and gets pretty hot inside the car in the daytime. This evening one of my sons wanted to "set free" some cicadas he had caught. I grabbed the LSH out of the car and it was quite warm. No problem in operation but is this okay for the light in the long run?

 

[jtice]

I would think it could handle it just fime, the battery is probably having a harder time with the heat than the LS is.
If you can still hold it in your hand, its fine.

Most LSs will get very warm if sat down while turned on, sence your hand isnt pulling some of the heat off.

 

[ledy]

I don't think you have to worry about that as long as you have decent battery. The LS itself is super hot when you turn it on, that heat transfer outside and make the bezel feels warm. When it's off and you can still grab it, the heat that transfer back into the LS is really minimal compared to when it's on.

 

[js]

Sakugenken,

Not a problem at all. The Arc LS's are designed to take higher temperatures than this continuously. And there is thermal protection which will cut-in in the event that the Arc ever does get too hot. IIRC, it's something on the order of 150 F.

 

[Sakugenken]

Thank you all for your answers /ubbthreads/images/graemlins/thumbsup.gif

 

[ledy]

js, I assume that the LS is not on when he leave it in the ash tray so the thermal protection is useless in this case.

 

[georget98]

I think the idea of having thermal protection is to keep the LED from going into thermal runaway: Ooooo, that's bright /ubbthreads/images/graemlins/smile.gif Wow, that bulb is hot /ubbthreads/images/graemlins/ooo.gif Oh, oh, it went out /ubbthreads/images/graemlins/frown.gif

So if the light is hot enough, then the circuit will prevent its coming on.

 

[ledy]

That's what I meant [useful for thermal runaway caused by the LED]. If the heat is coming from the sun, the thermal protection is not gonna make the sun (and therefore the light) any cooler. Anyway, I guess the main thing is that ARC light will have no problem sitting in the ashtray under the sun /ubbthreads/images/graemlins/smile.gif

 

[Sakugenken]

[ QUOTE ]
ledy said:
I guess the main thing is that ARC light will have no problem sitting in the ashtray under the sun /ubbthreads/images/graemlins/smile.gif

[/ QUOTE ]
Exactly! Althought the ashtray is not in direct sunlight the car interior does, of course, get really hot. The body of the LSH was warm the other night, before I even turned it on. I was worried about prolonged exposure to this heat damaging the light in some way.

 

[pbarrette]

Hi Sakugenken,

According to this website, if your car is in the sun for 1 hour or longer, you can basically take the ambient temperature and add 50F to that to find the likely temperature inside your car.

According to the lux datasheet (page 9), you should be able to operate a Lux at 350mA at an ambient temperature of 50C even if it has some pretty horrible heatsinking properties.

Assuming the LS has a pretty decent thermal path (which it looks like it does) and the Tj-a value is around 40C/W, then you should be able to operate the lux at 350mA if the ambient temp is ~75C (167F). Now that's freaking hot.. But apparently if you have the heatsinkning to do it, it should still keep the Tj lower than 120C.

Now, according to this from lumileds, a Lux operating at a case temperature of 85C (junction temp 105C) had a loss of ~10% of its light output after 2000 hours (83 days of continuous use). At the same time, a lux at 25C case (45C junction) showed no measurable lumen loss after 4000 hours.

So.. Unless it gets insanely hot where you live (like, over 40C), and you constantly leave the light sitting in the direct sun, then immediately turn it on before it has cooled, then I wouldn't worry too much.

A bit long, but it should be decent data. /ubbthreads/images/graemlins/smile.gif

pb

 

[ledy]

Now that's more scientific!. Good analysis.

 

[js]

[ QUOTE ]
ledy said:
js, I assume that the LS is not on when he leave it in the ash tray so the thermal protection is useless in this case.

[/ QUOTE ]

My point was not that the thermal protection would prevent damage from a hot glove box! My point was twofold:

1. If the light were so hot from sitting in the car that running it would damage the LED, then it simply wouldn't turn on until it had cooled off a bit.

2. That temperature (at which the thermal protection cuts in) is so high (150 F +) that a hot car and hot LSH will be no problem and nothing to worry about. If the LSH is so hot you can't hold onto it at all, then it's getting into dangerous territory, but other than that, it's not an issue.

 

[Sakugenken]

Thanks pbarrette! Your post has put my mind completely at ease. " a Lux operating at a case temperature of 85C...had a loss of ~10% of its light output" /ubbthreads/images/graemlins/ooo.gif If I ever pick it up and it is that hot, I will probably be more concerned about getting to an Emergency Room, than a 10% loss in output!