Date:         Fri, 3 Jul 2015 09:50:26 -0700
Reply-To:     Neil N <musomuso@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Neil N <musomuso@GMAIL.COM>
Subject:      Re: LED Headlight bulbs
Comments: To: David Beierl <dbeierl@attglobal.net>
In-Reply-To:  <559644b0.0ee98c0a.6a92.77f1SMTPIN_ADDED_MISSING@mx.google.com>
Content-Type: text/plain; charset=UTF-8

Thanks very much David.
That explains what my gut felt;
how can emitters do the same job as a filament.
Especially in a housing etc. designed for the latter.

I'm sure Jim will report back.

Neil.




On 7/3/15, David Beierl <dbeierl@attglobal.net> wrote:

> Optically they're utterly different from incandescents,  Headlights
> and such are designed to work with short line sources that radiate
> pretty uniformly into a sphere that looks more and more like a
> cylinder as they get longer.  The only way you can simulate that with
> an LED is to map a spheroidal surface some distance away and cover it
> with emitters -- but those emitters aren't unidirectional and shining
> only outward, they're themselves radiating into some portion of a
> hemisphere, so there's a bunch of stray light coming to the
> reflectors from the wrong direction.  You can make wonderful LED
> lights but you have to design for how they work, not use them as
> pretend incandescents in existing fixtures.  Not a problem for van
> cabin lights and such but no fixture with precise optical
> characteristics can fail to be degraded.  You may well get light
> where you want it, or mostly where you want it; but you will also get
> light in places where you specifically do not want it.  And getting
> it where you do want it, uniformly, means mapping onto a larger
> surface; where keeping it from where you don't implies going back to
> your point/line source.
>
> Yrs,
> d
>
>
>>Neil.
>
>


--
Neil n

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