LEDs as enlarger light source

I was doing some GOOGLE searches on LEDs to build a "poor-man's ZeeG-align"
and I am now wondering if anyone has experimented using white light LEDs to
replace the light source of enlargers? Heat could be greatly reduced,
perhaps eliminating the need of a fan in a Omega Dichroic II head (for
instance). For what I have read, there are also LEDs "bulbs" that would
screw in on regular bulbs sockets, meaning a condenser incandescent light
bulb could also be replaced by LEDs. Comments?

Guillermo

 

Well, the shape of the light source is radically different, and very tiny; I
don't think it would be a screw-in-the-bulb kind of conversion. But a
white-LED cold-light head ought to be a very fine thing: instant-on,
constant brightness, very little heat. Somebody needs to invent one!

 

There was a guy in the NET (IRC his name was Hun or Hus) that did a Vc head
using blue and green LED's (high power Lumileds).

Unfortunately, his site is gone and I've erased the bookmark.
But if someone is interested, I have a circuit he sent me (but I feel it's
incomplete)

Jorge

 

What does the spectral energy of a "white" LED look like?

Dana

 

Are you sure you don't mean Tim Shoppa ? His site is at ;

http://www.trailing-edge.com/~shoppa/led.html

IMO, it has wonderful possibilities but the cost isn't exactly low. Also I
have to wonder how much light output a bank of LED's can have.

BTW, the new high-output LED's are having a significant impact in lighting
today. Here's a link to a site that sells replacement lamps for incandescents
rated up to 200W.

http://members.shaw.ca/sagelighting/led_spotlights_and_bulbs_specifi.htm

Regards,

John S. Douglas - Photographer, Webmaster & Computer Tech
Please remove the "_" when replying via email
Website --- http://www.darkroompro.com

 

My guess is that there's about to be a very big revolution in lighting
generally. The humble incandescent light globe produces more heat
than light and has to be replaced after 1000 hours or so. LEDs last
for decades, so the marketers in the lighting industry will have to
come to grips with that somehow. (Although I have noticed that LEDs in
car tail and brake lights are starting to exhibit "industry standard"
failure rates- trust the car industry)

Back to enlargers: There was a thread somewhere and someone was
selling tri-coloured LED arrays for enlargers. For VC use, two would
be enough- green and blue. The trick would be to get uniformity,
shouldn't be too hard when you look at curved cold light tubes working
well. Intensity needs to be regulated, and there was a thread in
which someone had worked out a sophisticated circuit with intensity
feedback. LEDs vary in intensity, so maybe they'd have to be matched
(like power amp transistors in the old days)

Interesting topic. Let's hear from the engineers.

 

The spectrum can be found on any of the manufacturer's data sheets -- try
Agilent for a starter, Lite-on, Panasonic etc.

 

Google found the site, but with a new URL:

http://huws.org.uk/

But Tim Shoppa's article may be better for a condenser enlarger (I use
some like it as a red safelight).


Jorge

 

Forgot to add:
I exchanged some emails with Huws, and the 1W lumiled is bright enought
for normal times exposures.

Jorge

 

1 - It may be more expensive to implement, but forget about changing
lamps for your lifetime.
2 - Yes, intensity regulation would be a nicety - and fairly cheap to
implement.
3 - Since there will be (a lot?) of light diffusion, they do not have to
be matched.
4 - Each color string shall be series connected or the circuit will
become undully complex.

Now, all that's missing is a soldering iron...

Jorge

(John Stockdale) wrote in

 

One would think so.

To rain on the parade -- LED's don't have constant light output: they drift
with time for the first few months of on-time, LED-LED consistency is
the pits, they drift with temperature and they take 5+ minutes to stabilize
after they have been turned on as that the junction temperature stabilizes.
They _do_ generate heat (though they don't radiate it as a hot lamp
does) and are not very efficient. Oh, and the light output is slightly
polarized just for extra joy.

There is ought without a dark lining.

 

_Very_ nice piece of work.

 

Right up there with flourescents then. Anyone ever put a shutter in an
enlarger that didn't have one from the factory ?

Regards,

John S. Douglas - Photographer, Webmaster & Computer Tech
Please remove the "_" when replying via email
Website --- http://www.darkroompro.com

 

Seems alluring at first blush, but given the technical hurdles already
identified, I don't see where the declining market for conventional film
based enlargers would ever justify more than a meagre investment if any at
all. One of the first questions fore any new technical product is "Is the
market real?" Film based enlargers are a declining market. The answer
should be "No, the market is not real for a new light source in enlargers."

Just my thoughts.

PSsquare

 

A valid, and often profitable, business strategy is to go after an
increasing share of a declining market.

If one can accumulate share faster than the market declines then one
has a growth business.

Given enough time, the market for most anything will turn around due
to increased demand from an increasing population and from
3rd world markets coming on line.

Here in Ohio we have an expanding market for buggy whips, what
with the Amish and the country yuppies.

In the end everything dies: Capturing the market for slide-rules
is probably a dead issue for the foreseeable future.

 

Dam! and I was intending to sell my mint Hemi hyperbolog at a premium!

((-:

Jorge

 

My real point was that any light source needs to be evaluated for
spectral compatibility with the photosensitive materials in use,
and a visibly white LED might not be anything near truly white.
If I understand white LEDs correctly, they're either UV emitters
exciting a flourescent layer or they're monochromatic visible emitters
exciting a flourescent layer to broaden the perceived spectrum.

So, not all types of white LEDs strike me as equal.

Dana

 

I would not use a 'white' LED for color photos without a good test first.

Jorge

 

Is that a 426 Hemi Hyperblog ?

 

No, it's a 255D - bamboo, 12 inches

Jorge