Radiance and Song of Flame

Solution 1:

It seems that a lot of research has been done by the guy who started this thread: http://www.reddit.com/r/DestinyTheGame/comments/2skp25/sga_song_of_flame_and_how_it_interacts_with_stats/.

That post suggests that the user sees better reductions than those nearby.

It also says the range is 8m but the effect lasts for 5 seconds after you leave that range.

Other interesting things of note are that heart of praxic fire effects not just the warlock but those near him too.

More detailed analysis can be found there including exact figures for cooldowns on various combinations (ie 0 discipline, 100% discipline, etc.)

Solution 2:

According to this link it's 10 meters for allies.

http://www.destinygamewiki.com/wiki/Song_of_Flame