Hi Jo *mar,

You said an LED takes 20-30 minutes in a spot, could you direct me to some more information on this?

And do you think that's the case with this one? I suppose a lot of it can be trial and error. I'm just trying to be careful and get some benefits.

Amazon.com : Aweek(R) 96 Leds IR Illuminators Light IR Infrared Light LED infrared light CCTV Camera Night-vision Fill Light for CCTV Security Camera, Standard 45deg Level Angle Visual Range : Camera & Photo

You need to look for medical therapeutic type LED usually red/blue lights..

like these types-
Amazon.com: led light therapy pain: Health & Household