Many film and paper manufacturers post sensitivity curves. Most LED manufacturers also post emission curves. You could match that way. The problem is finding out which particular LEDs are in the product you buy. You could also just purchase your own LEDs of known make and emission curve and make your own safelight, very easy to do with a simple resistor and power source. I've used both red and amber LEDs in the darkroom for years without problems, and really like them. LEDs typically don't have a very wide spectral output. shows the output of the LEDs I use. Half-power spectral bandwidth appears to be about 25 nm with both the red and amber at recommended voltage/current.