Recently I started experimenting with the use of LED bulbs in enlargers. After some trial and error it now works great for me! I've noticed previous threads on this subject with different findings. I guess the LED bulb technology is still advancing so let me share my recent findings: I use Osram Parathom 4000K LED bulbs, 5 watt and 10 watt. I tried 2700K and 3000K bulbs and other brands but those all failed for me. The contrast at higher grades was too low: a grade 5 print with a 2700K or 3000K LED bulb was equal to a grade 3.5 print with a traditional bulb (Philips Photocrescenta 150w). A Philips 3000K bulb produced less contrast than an Osram 2700K bulb... strange. The contrast with the Osram Parathom 4000K is really the same as the Philips Photocrescenta traditional bulb, across the entire 0-5 range. What amazes me is the amount of light: the 5w and 10w LED bulbs produce much more light than the 150w Philips bulb, resulting in much shorter exposure times. Yesterday I printed a 20x24" (50x60cm), using a Leitz Focomat 1c, Focotar-2 lens at F/8, grade 5 filter, Ilford MG FB WT, Osram 10w LED bulb, exposure time 40 seconds. Less than half of what I needed with the Philips 150w bulb. The light spread of the LED bulb is fine. I also used the LED bulb in a Focomat 2c and here again the results were excellent. The advantages of using such LED bulbs are obvious: cheap, easy to purchase, no heat production (!), shorter exposure times. I'd be interested to hear what other experience using modern LED bulbs in enlargers.