From: Victor Roberts
Organization: Roberts Research & Consulting, Inc.
X-Mailer: Mozilla 4.78 [en] (Win98; U)
Subject: Re: luxeon star leds
References: <3DDD9A57.58900EFB@RobertsResearchInc.com> <email@example.com> <3DDDB646.96D0D9D2@RobertsResearchInc.com> <3DDE7264.CD48F4F8@RobertsResearchInc.com> <firstname.lastname@example.org> <3DDEB081.884EC92A@RobertsResearchInc.com> <3DE03D65.932BF9BF@RobertsResearchInc.com> <3DE15871.EF8FF9EA@RobertsResearchInc.com> <3DE224D3.81EFBA3C@RobertsResearchInc.com>
Date: Wed, 27 Nov 2002 13:11:26 GMT
NNTP-Posting-Date: Wed, 27 Nov 2002 05:11:26 PST
Bob Wilson wrote:
> In article ,
> email@example.com says...
> >In article ,
> >firstname.lastname@example.org talked about...
> >> Ooops, I missed that. But a luxeon without a heatsink would seem to be a
> >> 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 stabilizes
> >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 Lumileds
> 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 few
> moments, unless the heat spreader it is mounted to, is itself mounted to a
> PROPER heatsink.
> If you run a Luxeon LED (either the single LED, or the 12-LED Luxeon Line)
> 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 the
> 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 are
> 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