An imagined LED enlarger light source for 4x5

[Ulophot]

Hello. I started thread over at large format info recently that may be of interest here as well. Perhaps someone here will have additional ideas. The link is here:
https://www.largeformatphotography....light-source-for-4x5-NEW-INFO-FOR-TECHNICIANS

In brief, I raised my concern that our cold light heads (B&W, such as Aristo, Zone VI) will not last forever, and, since I can't build anything of quality myself, ventured an uniformed guess at how such an item might be made. I was duly corrected. However, there were some new ideas also. I continue to think that it's a good time to propose a simple, white-light LED device to cover 4x5 and be able to fit, modularly, to various widely used enlargers, e.g., Omega D series, LPL, Durst.

I am aware of the Heiland -- great for those with the money. Many of us are happy with Ilford or other filters for VC paper use and would like a simpler source to replace our current diffusion cold lights. In my case, I no longer have the condenser or standard lamp top of the enlarger. I could probably buy one, but I'm interested a flat LED panel if possible; it makes sense.

I don't expect one to appear tomorrow. I just wish to poke around and see what potentials there may be.

 

[MattKing]

Sounds like Modern Enlarger Lamps -- wish he had been able to keep operating: http://www.modernenlargerlamps.com/Modern_Enlarger_Lamps/Welcome.html

 

[Donald Qualls]

Not long ago, I ran across "can fixture" replacements in LED -- these replace "recessed lighting" in places like kitchens and bathrooms with a flat LED panel at the surface the old style "can" light would recess into.

They come in sizes suitable for medium format, 4x5, and even 5x7 enlargers, and appear to have very even light across the surface (though what appears in a brochure type illustration says very little about how even exposure will be in an enlarger).

They run directly on 120V (or if you're in Europe, in 240V), don't much care about frequency (50 or 60 Hz doesn't matter since the current is rectified before it powers the LEDs), and are quite inexpensive -- I recall one that might replace my old Zone VI cold light costing around $25-$30. With LED efficiency, a power draw of 25 W would be equivalent to a 100W or better incandescent lamp. They'd be diffuser sources only, of course -- but many workers prefer that sort over the grain-emphasizing sharpness of a condenser with a small light source.

 

[DREW WILEY]

I'm shocked at some of these designs offering I-Phone control. Given the fact that phone specifics seem to have the lifespan about as long as a fruit fly before something later and greater comes out, that might not be such a great idea.

 

[btaylor]

Donald, that sounds like a great idea. Home Depot has 6” units for $20. Simple!
I built a flat panel LED light source for my 10x10 Omega F. I think the panel was $80, I used a couple of picture frames from Target for spacers and a couple of sheets of Roscoe diffusion to smooth out any unevenness and use under the lens Ilford contrast filters. It works.

 

[Ulophot]

Regarding these Home D units, does the light fade slowly when turned off, the way many LED traditional-shape light bulbs do? If so, I don't see them working very well for enlarging, at least with my approach. My timer allows brief exposures of seconds and tenths thereof, which I use in multiples, rather than long single exposures. Repeatability is, of course, vital. Also, the 6" round I see is rated as 65W equivalent, which is on the lower end of usability, I suspect. I'd be interested to hear more about your procedures and results.

 

[Donald Qualls]

Regarding these Home D units, does the light fade slowly when turned off, the way many LED traditional-shape light bulbs do? If so, I don't see them working very well for enlarging, at least with my approach. My timer allows brief exposures of seconds and tenths thereof, which I use in multiples, rather than long single exposures. Repeatability is, of course, vital. Also, the 6" round I see is rated as 65W equivalent, which is on the lower end of usability, I suspect. I'd be interested to hear more about your procedures and results.

No idea on any of those questions. I've never seen one in operation. I do agree, 65W equivalent seems a little on the dim side, even for the intended purpose (these are replacing ceiling recessed fixtures that might well have 150W reflector floods in them).

Slow fading light seems like the mark of a large filter capacitor in the rectifier circuit -- I have a hunch the "dimmable" LED units will have much less of this problem than the standard ones, because they need to respond to the SCR dimmers in a way reasonably similar to incandescent or halogen lamps -- and SCR dimmers work by changing the duty cycle of the power to the lamp.

 

[DREW WILEY]

Most of what Cheapo Depot sells is horrible import junk, just like WalMart. If you can plug it in, it is probably capable of burning your house down somehow. Even phony UL labeling is routine for certain import channels.

 

[Kilgallb]

I made an LED light source from a Pot light I found at Lowe’s. it is a 20W lamp equivalent to 100W tungsten. I fitted it to the top of a beseler 4x5 mixing chamber. It works well. It is dim able and seems to turn on and off as fast as a tungsten lamp. It is a Philips lamp.

The spectral content is not the same as tungsten so a GRADE 5 filter is 2 stops slower instead of 1 stop.

 

[Mal Paso]

4X5 really needs a 6.5 inch diameter source to cover. For Beseler it must fit into a 6 5/8 inch hole. I converted a non working Beseler 45a Cold Light Head to LED. https://www.photrio.com/forum/threads/led-split-printing-enlarger-lamphouse.173834/

I wanted a VC cold light head but had concerns about the future of tubes. LED also offers improved stability with inexpensive regulated power supplies and drivers.

 

[koraks]

Slow fading light seems like the mark of a large filter capacitor in the rectifier circuit

Yes, that's one possibility. Another one is that many white LED bulbs are in fact UV leds with the bulb having a phosphor coating that converts the UV into a broad/continuous bandwidth white light. These phosphors have the tendency to exhibit afterglow. In most LED bulbs I've come across that exhibit an afterglow issue, this seems to be the main cause, not so much a capacitor discharge.

 

[Donald Qualls]

Yep, phosphor afterglow is why I don't want/allow CFL in the white room light in my darkroom. Flip the light off, and it'll still fog my film for longer than it takes to load a daylight tank (on a flat counter -- takes longer in a changing bag). I need to remember to check/test that on the LED bulbs I plan to buy for the overhead white light. Not sure how to do that without spending money on stuff that I won't be able to use -- can't really test that in daylight in the lighting section at the Big Box. Might start a new thread in Darkroom Equipment to see if anyone has brand/type recommendations.

 

[Ulophot]

Mal Paso, thank you very much for the link. I have passed it on to someone who is looking into this issue now. Much appreciated.

4X5 really needs a 6.5 inch diameter source to cover. For Beseler it must fit into a 6 5/8 inch hole. I converted a non working Beseler 45a Cold Light Head to LED. https://www.photrio.com/forum/threads/led-split-printing-enlarger-lamphouse.173834/

I wanted a VC cold light head but had concerns about the future of tubes. LED also offers improved stability with inexpensive regulated power supplies and drivers.

 

[Mal Paso]

I use Costco LED shop Lights for darkroom setup and cleaning. They shut off instantly but the Darkroom floor is wood. When they were over concrete they would glow slightly when shut off. It was capacitance to ground and the efficiency of LEDs. Had to pull the plug to turn them off.

I have a 7 watt LED reflector flood over the fixer tray on a dimmer with a paddle switch. It takes a couple seconds to go completely black but it's fully off by the time I could get paper out.

The enlarger LEDs run on Drivers that are always on with a preload on the inputs. There is no residual light after shut off because the stored energy is in the power supply on the other side of the driver from the LEDs. On is faster than mechanical relays.

Safelights are 3 watts I think. The only tungsten bulbs in the darkroom are 3 condenser spares.