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Subject: Re: luxeon star leds
Date: Thu, 28 Nov 2002 18:50:13 -0800
Organization: SCN Research of Tigard, Oregon, USA.
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> <3DE3FAE4.51FB1D22@RobertsResearchInc.com> <3DE4C652.4000B465@RobertsResearchInc.com>
NNTP-Posting-Date: Fri, 29 Nov 2002 02:50:24 +0000 (UTC)
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Also note the devices actually emit more light when the die temperature
is kept low...
"Victor Roberts" wrote in message
> Victor Roberts wrote:
> > Watson 'Atto Parsec' Name wrote:
> > >
> > > In article ,
> > > firstname.lastname@example.org talked about...
> > > [snip]
> > >
> > > > Ooops, I missed that. But a luxeon without a heatsink would seem to
> > > > 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
> > > > ordinary LEDs.
> > >
> > > The Luxeon has a _built-in_ heatsink. Somewhere I read that it
> > > 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
> > words.
> > 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.
> Vic Roberts
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