... got a 16mm Ruby sphere and tested it on a 405nm-LED with 500mW optical output (the LED can emit up to 9Watts, but will need water cooling then).
Here a video, showing the LED alone and with the Ruby sphere at max. 500mW output of 405nm - https://vimeo.com/285334438
And some images:
For the human eye the glow stay red and will get only more intensive ... the camera is saturated at some hundred Milliwatts from the LED!
Could be pretty interesting at max. 9Watts from the LED ... or with 3 of this 9Watt-LED's arranged around the "Äquator" of the sphere and two concave mirrors (one semi-transparent) on the "poles" focussing into the center of the sphere ...
Viktor