[pure-silver] Re: LED light source (was Re: Re: VC printing equipment ...
- From: "Claudio Bonavolta" <claudio@xxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sun, 19 Sep 2004 11:38:46 +0200
----- Original Message -----
From: "Rei Shinozuka" <shino@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Saturday, September 18, 2004 8:32 PM
Subject: [pure-silver] LED light source (was Re: Re: VC printing equipment
...
> every once in a while i consider getting a VC cold-light head. (currently
> i have a 45A flashtube head which refuses to die). lately i noticed
> that calumet/zone vi has a 4x5 LED light source, which in theory sounds
> like an impressive innovation.
>
> i was wondering what the inside scoop was on this thing.
>
> thx,
>
> -rei
Hi Rei,
Once my computer-driven timer* will be finished (by the end of the year),
I'll start a LED head for my Focomat IIc.
Leds are not a new thing, what is new is their enormous rise in power and
light output these last years.
You can see it everyday as leds are used now for nearly all new cars brakes
light or in traffic lights (red, green and amber).
The project by Tim Shoppa mentioned by John uses already old types, that's
the reason he needed a large number of leds mounted in an array.
Go to this page to see actual very powerful leds: http://www.luxeon.com
Here is a brief summary of their advantages:
- although not a pure wavelength (as a laser), they emit in a very narrow
spectrum.
- RGB led system can be used in an additive head either for multigrade
(Green and Blue) or color (+ Red)
- no IR and UV emission at all (but high-power leds *must* be cooled)
- rise/fall time below the microsecond, this means they react much faster
than a camera shutter. This also means that very short exposures times will
be precise. This means also new ways of exposing paper may be imagined.
- dimmable either through current variations and/or fast switching without
change of color.
- efficiency is somewhat less than fluorescent tubes but much higher than
tungsten/halogen
- as they require an electronic circuitry to drive them, light output is
easily very constant (no need for any voltage stabilizer or closed-loop
circuitry).
- light output during component's life much more constant than other sources
- life expected in a range of 50'000hrs (compare it to a 1000-2500 hrs of an
halogen bulb)
- low-voltage, leds are current-driven.
Others characteristics, not very important in an enlarger
- point source. As a single led can't actually drive completely the
enlarger, it'snot useful. But may be in the future.
- very directive light emission, no need for reflectors. The built-in optic
is sufficient.
- cold start capable
- solid-state, resistant to mechanical stress
- no mercury
Drawbacks:
- white leds don't have a very flat spectrum (which we don't care much in
our appliance)
- light output still somewhat low for very large enlargers
- design/construction difficulties
- cost
In conclusion, this is a *great* light source alternative and the reason
I'll go that route.
* http://www.bonavolta.ch/hobby/en/photo/labsoftV3.htm (a major update
should be done in a couple of weeks).
Regards,
Claudio Bonavolta
http://www.bonavolta.ch
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