Will LED light therapy work to fade a bruise that will not totally fade?

Thanks for your question. LED treatment could possibly help. A more targeted option could also be V Beam Laser Treatment. The most advanced Pulsed Dye Laser Technology, VBeam treats red skin, broken blood vessels, rosacea, birthmarks, as well as bruises. This laser targets the selected area with an intense yet gentle burst of light. This laser is so safe that it’s used for the treatment of port wine stains on infants and young children. Hope this helps! 

You would likely significantly benefit with a 590nm light therapy. The wave length is a frequency isolated form a broadband light therapy. 
Most providers providing broadband light (BBL) therapy will have the proper filters and be able to isolate the frequency. Works very will on bruises. One or two session should do the trick. 
Hope I have helped.
Warmly,
Arbella Sarkis, MD