From: email@example.com (Bob Wilson)
Subject: Re: luxeon star leds
Date: Thu, 28 Nov 2002 03:42:19 -0000
Organization: Your Organization
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References: <3DDD9A57.58900EFB@RobertsResearchInc.com> <firstname.lastname@example.org> <3DDDB646.96D0D9D2@RobertsResearchInc.com> <3DDE7264.CD48F4F8@RobertsResearchInc.com> <email@example.com> <3DDEB081.884EC92A@RobertsResearchInc.com> <3DE03D65.932BF9BF@RobertsResearchInc.com> <3DE15871.EF8FF9EA@RobertsResearchInc.com> <3DE224D3.81EFBA3C@RobertsResearchInc.com> <3DE4C4C1.50072B92@RobertsResearchInc.com>
In article <3DE4C4C1.50072B92@RobertsResearchInc.com>,
>Bob Wilson wrote:
>> In article ,
>> firstname.lastname@example.org says...
>> >In article ,
>> >email@example.com talked about...
>> >> Ooops, I missed that. But a luxeon without a heatsink would seem to be
>> >> complete waste of an expensive LED. Without a heatsink, it is not
>> >> to push it to anywhere near its intended power level, May as well just
>> >> ordinary LEDs.
>> >The Luxeon has a _built-in_ heatsink. Somewhere I read that it
>> >at 60 deg without any external HS.
>> That is completely incorrect. There are versions of the Luxeon LEDs that
>> come mounted to a metal core PCB. This is NOT a heat sink, in fact
>> strongly warns in its literature (which is posted on their Luxeon website
>> for all to see) against operating the LEDs at full power for more than a
>> moments, unless the heat spreader it is mounted to, is itself mounted to
>> PROPER heatsink.
>> If you run a Luxeon LED (either the single LED, or the 12-LED Luxeon
>> at full power, with only the heat spreader attached, the LED(s) will be
>> damaged by overheating in a few minutes. In fact, this is pretty obvious,
>> looking at the size of the heat spreader. Taking the single Luxeon with
>> attached ~1" square metal core PCB attached to it, as an example, it is
>> obvious by inspection that this will not stabilize at only 60C, when you
>> pumping a Watt into it.
>Even though I also disagreed with the original poster that
>the small aluminum-core PCB would stabilize at 60C, I have
>found the reference he may have used. There is a small data
>sheet with the Luxeon logo inside plastic bag with the
>Luxeon Star/O LED sample I received at Light Fair 2001. It
>says "For sustained operation please ensure that the unit is
>properly mounted to a secondary heatsink. The back surface
>of MCPCB will stabilize at 60C without any additional
>Based on this, the junction temperature would be about 77C
>to 80C at full power input. HOWEVER, I expect the 60C
>number was measured with the MCPCB mounted in free air, and
>I don't believe that would be typical in most applications.
>The LED would usually not be "suspended" in free air, it
>would be mounted to something, and if that something was not
>thermally conductive then the MCPCB would not have the
>benefit of free air convective cooling and would run at
Well, I wouldn't trust it too much. We found that a single Luxeon mounted to
the ~1" square metal core PCB got significantly hotter than 60, and got
there pretty fast.
The Luxeon Line product (12 LEDs mounted on a long metal core board) did a
little better, but still at 60C the light output has already dropped
somewhat, and the life will be significantly reduced.