Message-ID: <3DE2F27F.DDF7750C@RobertsResearchInc.com>
From: Victor Roberts
Organization: Roberts Research & Consulting, Inc.
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Newsgroups: sci.engr.lighting,sci.electronics.design,sci.electronics.components,sci.engr.lighting
Subject: Re: luxeon star leds
References: <3DDD9A57.58900EFB@RobertsResearchInc.com> <7k9rtu4o0ies1vv2dq38ofphss9rug168t@4ax.com> <3DDDB646.96D0D9D2@RobertsResearchInc.com> <3DDE7264.CD48F4F8@RobertsResearchInc.com> <162ttusrr79apgodiutf0e2r37a14pth6c@4ax.com> <3DDEB081.884EC92A@RobertsResearchInc.com> <3DE03D65.932BF9BF@RobertsResearchInc.com> <3DE15871.EF8FF9EA@RobertsResearchInc.com> <3DE224D3.81EFBA3C@RobertsResearchInc.com>
Date: Tue, 26 Nov 2002 04:02:14 GMT
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NNTP-Posting-Date: Mon, 25 Nov 2002 20:02:14 PST
Bob Wilson wrote:
>
> In article <3DE224D3.81EFBA3C@RobertsResearchInc.com>,
> Vic@RobertsResearchInc.com says...
> >
> >Bob Wilson wrote:
> >>
> >> In article <3DE15871.EF8FF9EA@RobertsResearchInc.com>,
> >> Vic@RobertsResearchInc.com says...
> >> >
> >> >Watson 'Atto Parsec' Name wrote:
> >> >>
> >> >> In article <3DE03D65.932BF9BF@RobertsResearchInc.com>,
> >> >> Vic@RobertsResearchInc.com talked about...
> >> >> > Watson 'Atto Parsec' Name wrote:
> >> >> > >
> >> >> > > I don't buy this convection from the top because I'm using the
> Luxeon
> >> >> > > Star/O which has the whole top of the LED covered by the lens
> >> assembly.
> >> >> >
> >> >> > You are certainly entitled to your opinion, but don't you
> >> >> > think that the lens assembly will have convective losses
> >> >> > when it gets hot? The lens assembly will, of course, get hot
> >> >> > under steady state conditions if the metal base is not
> >> >> > conected to a heat sink. Considering that the lens assembly,
> >> >> > including its cylindrical holder, has a much greater surface
> >> >> > area than the top of the "bare" Luxeon Star, the "convective
> >> >> > effect" should be more pronounced for a Luxeon with the lens
> >> >> > assembly than for one without.
> >> >>
> >> >> The heat from the aluminum base will conduct up thru the barel of the
> >> lens
> >> >> assy and be 'convected' away, as much if not moreso than the internal
> >> heat.
> >> >
> >> >That's a good point.
> >>
> >> Interesting that it is expected that any significant amount of heat will
> be
> >> conducted up through an insulating plastic barrel, that is only 1mm
> thick.
> >> Even more interesting how this can be expected to be significant, in view
> of
> >> the Luxeon LED itself, being mounted on a metal core PCB, and that being
> >> mounted to to a heatsink. Quite obviously any small amount of heat
> >> that manages to be conducted up the small cross section of insulating
> >> plastic barrel, will be totally insignificant when compared to that which
> >> flows through the large area of 0.1mm thick FR4 laminated to the aluminum
> >> backing directly behind the metal base of the LED, and directly into a
> >> heatsink.
> >
> >You are correct, if the Luxeon were mounted on a heatsink.
> >However, this whole discussion started because of some
> >unexpected results that were published about a Luxeon that
> >was NOT mounted on a heatsink.
>
> 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.
I believe this was just for a test of forward voltage vs.
junction temperature.
--
Vic Roberts
http://www.RobertsResearchInc.com