Tested an LED Light Bulb for Contact Printing in the Darkroom

December 06, 2015  •  6 Comments

I have been using incandescent light bulbs in the darkroom for over 30 years to make contact prints.  I was motivated to explore the viability of using an LED light bulb because I am building an off the grid darkroom that is powered by solar and wind and I will be using both 12V LED lights and also the A/C versions to help reduce my power consumption.

LED lights use significantly less power than incandescents and they have the added benefit of lasting for decades.  I wasn't really sure what to expect, so I setup a test and made a test contact print.  

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I laid one of my light meters on the work surface and switched it to EV mode.  I turned on the 15W incandescent bulb and measured a light value of 2.9.  I then switched out the LED light and I knew that I would have to reduce the output of the lamp because the smallest LED light that I could find was a 40W equivalent.  On a side note, the LED lamp only consumes about 4W, which is a big savings for me over time.  I metered the light from the LED light without and dimming and it was 4.1, which was way too high.  I used the special dimmer that is made to work with LED, CFL and Incandescent until I got the value to match at 2.9.  

Then I ran a 3-second test strip increment from a print that I just tested earlier today and they were effectively identical.  This simple test confirmed that I can use LED lights in my darkroom for contact printing now.  

I look forward to your thoughts and comments.

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Pablo Coronel(non-registered)
After many years of using incandescent, and given the price of LEDs, I repalced the bulb in my 6x7 enlarger with an off the shelf 75W bulb (out of curiosity)
Light is even on the enlarging board, and the 75W LED seems to be 1/3 stop brighter than the incandescent (which itself is 15+ yr old)
Contrast seems to be a tad on the harder side than the incandescent bulb (1/2 step) but perfectly doable...
an not only there is no negative pop, but the whole room feels cooler
Tim Layton Fine Art
Hi Paul, thank you very much for commenting and sharing your information. It is an exciting and changing time for sure. Keep all of us posted on your work with LED lights. Thanks, Tim.
Paul Glover(non-registered)
I had a good deal of success split grade printing in a condenser enlarger using a household LED (60W equivalent) and a pair of primary blue and green filters. My main motivation was to get rid of severe heat-induced negative pop issues. Had to jury-rig a lamp holder which positioned the bulb properly.

Now that LED bulbs are reasonably priced and I've replaced all the CFLs around our apartment, I've noted that some of them are not ideal for use when timing is critical. I have some which turn on instantly but fade out noticeably when turned off. Some others take maybe half a second to come on (though they at least do it consistently, and light to full brightness immediately unlike CFLs).

I'm much more excited about the relatively affordable LED modules now available, and have had good results with a royal blue and green (with a red or deep red for safe viewing of the image); controlled by a microcontroller-based timer. The whole thing can run on a 12 volt supply, and could also use red LED modules for safelighting.
Tim Layton Fine Art
Hi Rolf, my test was very basic and based on 99% curiosity and less than 1% science. My initial impression is that the LED performed the same as the incandescent under the conditions that I used it when the lumen output was metered to be the same. More practical application ahead. Thanks!!
Rolf Schmolling(non-registered)
Hi Tim, interesting to read about your test. Thank You for your post!

As I told you I have not yet finished my LED conversion and never tried it. From what I have read on forums specialized in darkroom work etc. 1) the spectrum of most LEDs is often not the same than with an incandescent bulb, some parts of the spectrum missing, even though the overall color temperature are according to the specs advertised. That could or need not to influence the reaction of multigrade papers. 2) seems for most LEDs it's difficult to get the exact specs/graphs. So we will have to try and find through trial and error a brand which is ok, and test for available grades and response to multigrade filtering (or not). Someone exposed a Stouffer wedge 4x5 negative (not as a contact afaik) and checked what different contrast variants he got with different filters. In his case it seemed to have worked out. That's something I will try out when I finished the conversion head… I wonder if you had a look at these two sites: http://www.jonathangazeley.com/2014/06/further-modifications-to-the-de-vere-54/ (there are more recent posts I am referring to, with an LED lighting panel and some testing); http://www.trippingthroughthedark.com/variable-contrast-led-head-for-durst-138s-condensers/ (building a variable contrast head with LEDs for a Durst 138).
Have stil to watch your video on contact printing of paper negatives, too tired right now, off to bed… R.
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