From: Watson 'Atto Parsec' Name
Subject: Re: luxeon star leds
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>
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Date: Wed, 27 Nov 2002 08:18:11 -0800
NNTP-Posting-Date: Wed, 27 Nov 2002 09:16:28 PST
Organization: InReach Internet
In article <3DE4C4C1.50072B92@RobertsResearchInc.com>,
Vic@RobertsResearchInc.com talked about...
> Bob Wilson wrote:
> > In article ,
> > firstname.lastname@example.org says...
> > >
> > >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.
> > 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
Thank you for confirming my statement.
> 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
> higher temperature.
I have mounted my Star/O LEDs on small pieces of metal brackets inside of
project boxes. They do not have a problem with overheating even tho
they're totally enclosed. You have to remember that the plastic itself
conducts heat, as does a PC board. I have run them at full power for
perhaps a half hour or more and they don't seem to get hot. On the first
one I built, I used a piece of 1" wide by 4" long copper, bent into an 'L'
shape of 1 by 3 inches. It is mounted inside of the box, with the LED
mounted to the 1" upright part. It barely gets warm. So with later ones I
made I used a much smaller bracket of aluminum. Works just fine.
One guy, Lambda, makes a Mini Maglite conversion called the Ill Pill which
does not use a heatsink. I believe the LED is held on the flashlight with
a piece of rubber. AFAIK, there hasn't been a problem with overheating.
If you're serious about all this speculation that has been discussed, I
suggest you assemble a Star/O into a working device and use it, and then
come back and tell your experiences. I don't think you will then be so
critical of the heat problem.
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you put NOSPAM in the
Subject: line. alondra101 hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html