As has been said, it all depends on the LED. The graph in the earlier post shows a pretty typical LED spectrum. SuperLEDs have a somewhat narrower linewidth. The problem is that some hight intensity LEDs operate at a shorter wavelength (more yellow), partly because the eye is more sensitive there. If you stick with the 645 to 660 nm red LEDs you shouldn't have any problem. I have used a pretty bright LED safelight with orthochromatic materials (like Kodalith) and paper with no problems at all. As for comparative brightness, they are quite bright, but the usual multi-LED module is nowhere near as bright as the Thomas safelight (which I find far too bright). The deep yellow and orange (590 - 620 nm) LEDs should also work well with the usual papers. (Forma claims to need deep orange or red safelights.) If you hunt hard you may even find LEDs that emit at 602 nm, which matches the Series 13 safelight filter for Kodak color papers. As with any safelight, a test should be done with the materials you intend to use. One decided advantage of LEDs is that they start instantly, so you can connect them to the enlarging timer. They are also miserly on power. Although LEDs have an inherently long life, they are sensitive to line spikes and surges, which can burn them out quickly.