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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> <3DE3FAE4.51FB1D22@RobertsResearchInc.com>
Date: Wed, 27 Nov 2002 13:18:09 GMT
NNTP-Posting-Date: Wed, 27 Nov 2002 05:18:09 PST
Victor Roberts wrote:
> Watson 'Atto Parsec' Name wrote:
> > In article ,
> > email@example.com talked about...
> > [snip]
> > > 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 possible
> > > to push it to anywhere near its intended power level, May as well just use
> > > ordinary LEDs.
> > The Luxeon has a _built-in_ heatsink. Somewhere I read that it stabilizes
> > at 60 deg without any external HS.
> I'm not sure I would call the aluminum-core PCB a "heatsink"
> since it is designed for connection to a real heatsink, but
> it is probably not productive to debate the meaning of
> My Luxeon datasheet states that the maximum operating
> temperature for the aluminum-core PCB is 105C. There is also
> a note on the maximum current specification of 350ma that
> "Proper current derating must be observed to maintain
> junction temperature below the maximum." I have not
> calculated the temperature of the aluminum-core PCB in free
> air conditions when it is dissipating 1.1 watts of power,
> but this caution from Lumileds leads me to believe that this
> device will overheat if operated at full current without use
> of an external heatsink.
> Even if the maximum junction temperature of 120C is not
> exceeded by operating the Luxeon without an external
> heatsink, the Luxeon datasheet clearly shows that both the
> initial efficacy and the lumen maintenance will be
> significantly degraded if the LED junction is operated at
> high temperature.
> If you have a reference for the statement that the
> aluminum-core PCB will stabilize at 60C without an external
> heat sink I would be interested finding out where that
> information came from.
I found a reference to the 60C that "Watson" may have used.
See my other note for a longer explanation, but the comment
is on a small paper datasheet enclosed with the Luxeon LED
sample I obtained at Light Fair 2001. However, as stated in
my other note, this must be for the case where the MCPCB is
mounted in free air so it can be cooled by free air
convection. Obviously if a heat sink is not used, the MCPCB
would likely be mounted on a thermally insulating substrate
which would certainly raise the temperature of the MCPCB. In
any case, 60C on the MCPCB implies a junction temperature of
77C to 80C at full power which will reduce output and
increase the rate of lumen depreciation.
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