The idea is simple: create large enough media surface, assign colorful Youtube video to it and enable Global Illumination in Experience settings. After publishing process there will be really impressive effect - Global illumination will propagate light everywhere from that youtube video on media surface, changing in real time! Here is how it looks:
Did this for my map "City park" but unfortunately got tons of Global illumination artifacts :( and this cool feature did not present in final version of my Experience *yet*:
But if it's working fine enough for you - use it, artifacts may not appear or be in moderate amount. Have fun! :)