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  1. #21  
    see my post--hopefully you will start using it again. :-)

    The emitter is also sitting on top of a small metal box (can't see it in the pic).

    So basically, the emitter is NOT just sitting on a pcb. There *is* some metal to act as a heat sink.
  2. #22  
    Quote Originally Posted by DrHeathenScum View Post

    I'm going to stick with my Photon Micro-Light on my keychain.
    I think you should know that the Photon Micro-Light actually does slightly overdrive the 5mm Nichia. Brightness of the LED after a few battery changes is noticeably dimmer.
    :-)

    Get one of these lights for a really cool pocket light:
    Skunklights * Home
    (my side hobby)
  3.    #23  
    Quote Originally Posted by rogerkang View Post
    I think you should know that the Photon Micro-Light actually does slightly overdrive the 5mm Nichia. Brightness of the LED after a few battery changes is noticeably dimmer.
    :-)
    LOL. I know, but they're only ~$15 to replace.

    Get one of these lights for a really cool pocket light:
    Skunklights * Home
    (my side hobby)
    Will check that out... I like lights.
  4. #24  
    Quote Originally Posted by Thead View Post
    My light probably gets around 30-45 minutes of use a week from walking outside at night. My assumption is that while it may reduce the life of the LED, I will have upgraded to a new phone loooong before that will ever happen.


    ^ Exactly!!!
    Are bad people born that way? Or did something go terribly wrong?
  5. #25  
    Quote Originally Posted by DrHeathenScum View Post
    LOL. I know, but they're only ~$15 to replace.



    Will check that out... I like lights.
    Me, too. You should check out CandlePowerForums

    This is where "flashaholics" talk about the latest and greatest high power LED lights, HIDs, etc.

    For $20, you can buy a 3 level (med/low/high) AAA keychain light that is really small (just a bit bigger than the AAA battery) and has a high power Cree XP-E emitter. 80 lumens on high.
    http://goinggear.com/index.php?main_...roducts_id=255

    Join candlepowerforums and you get a discount at a lot of these kinds of stores, too.

    Beats the crap out of a photon 5mm light.


    The Pre's LED flashlight is great for times when you don't have a handy flashlight, but if you have one of these lights on your keychain, you can save the Pre's flashlight for only those times when you *really* need a flashlight.
  6. #26  
    Quote Originally Posted by rogerkang View Post
    Yes, I am aware of how much heat it generates. But if properly heat-sinked with good thermal pathways to the flashlight body, you won't notice it much *if you are holding the light* and not leaving it alone on a table, etc. where it can get hot on its own.

    Your body does a surprisingly good job of keeping the flashlight temp down (when you are holding the light in your hand).

    For a 3W LED to be driven at 3W, you're talking roughly 3.2v - 3.3v (for the latest Cree XP-G emitter, for example) x around 920mA of current. That's pretty high, although I admit it's not overdriving the LED like some lights.

    Yes, I am assuming that the above poster does not have the most efficient light but more of a "brightness counts" light. It seems like so many lights made today emphasize brightness and NOT efficiency of the LED (like driving it at 350 or 500mA for optimal efficiency).

    For the camera flash LED, we are talking an emitter that is being driven at 50mA - 200mA, depending on which setting you use. (I am assuming the use of Jason's flashlight torch app.)
    I doubt the emitter is spec'd out to be driven below this. Short use should be OK. But then again, I'm not sure if flash LEDs used in cameras these days come with shorter lives than other LEDs. Probably not too significant. I mean, if you decrease the life of the flash LED from 10,000 hours to 1,000 hours, what's the big deal? Most people will never use their flashlight for 1,000 hours, etc. Most Pre users will be on to their next WebOS phone by the time the LED starts to dim noticeably.
    Well, this thread turned out to be pretty informative. And yea, most likely the LED light that I have does emphasize light output over efficiency. 190 Lumens from 1 lithium primary cell does seem pretty crazy. I'm a bit of a flashlight junkie, and have visited CPF quite a few times.

    I wonder, is there any way to measure the amount of current going to the LED bulb in the phone? Without causing damage of course. Even given all this information, I would think that the LED will outlast the phone, even if it is used as an occasional flashlight.
  7. #27  
    Quote Originally Posted by sputnik767 View Post

    I wonder, is there any way to measure the amount of current going to the LED bulb in the phone?

    The only accurate way of measuring the current would be to unsolder one of the leads to hook it up to a meter and this means taking the Pre apart, unfortunately. I don't think I want to do this. (Was up until 4am last night modding a flashlight, actually!)

    BUT...if the LED ever dies, I will probably mod it and put in a nice suitable replacement. :-) And then I can measure it at that time.

    I guess you could measure the heat at the emitter w/ one of those fancy temperature guns...this might be better than nothing. I've always wanted one of those. Maybe I should buy one now, as this is the perfect excuse. :-)

    EDIT: Actually, I just realized that Jason R's flashlight app lets you dial in the current going to the LED (50mA, 100mA, or 200mA).
    So what we really want to know is how much heat is being generated around the LED when it is operation...(which was really the OP's concern).
  8.    #28  
    I would go out on a limb and say running it @ 50mA would cause little concern, even without knowing the LED specs and how the PCB is made/assembled.
  9. jp99's Avatar
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    #29  
    I'm an LED system thermal engineer, and I have a little inside knowledge of how the LED is heat sunk in a certain cell phone whose name has 3 letters. I've also talked with the thermal engineer in charge of it.

    While the system doesn't go into catastrophic temperature rises, the junction temperature is quite high and the unit is designed for transient use, not continuous. That said, I chose not to use the flash as a flashlight in continuous mode. I'd rather not degrade the light output (your eye won't detect any light drop until you've lost at least 25% anyway).

    Those talking about LEDs and heat - they do put out heat; about 75% of the input energy goes out the backside as heat (for white). A filament bulb is more along the lines of 90%. It happens to be more directed light, so you need a smaller light source, but you must have the proper path for heat conduction away from the LED package. A poor path means high temperatures in the LED. The thermal design of an LED luminaire is often the most challenging part of the design.
  10.    #30  
    Quote Originally Posted by jp99 View Post
    I'm an LED system thermal engineer, and I have a little inside knowledge of how the LED is heat sunk in a certain cell phone whose name has 3 letters. I've also talked with the thermal engineer in charge of it.

    While the system doesn't go into catastrophic temperature rises, the junction temperature is quite high and the unit is designed for transient use, not continuous. That said, I chose not to use the flash as a flashlight in continuous mode. I'd rather not degrade the light output (your eye won't detect any light drop until you've lost at least 25% anyway).

    Those talking about LEDs and heat - they do put out heat; about 75% of the input energy goes out the backside as heat (for white). A filament bulb is more along the lines of 90%. It happens to be more directed light, so you need a smaller light source, but you must have the proper path for heat conduction away from the LED package. A poor path means high temperatures in the LED. The thermal design of an LED luminaire is often the most challenging part of the design.
    Thank you.
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