[Christien]

I'm sure it's true, from a physics standpoint: the single burning candle is releasing heat (and light) energy into the room. If you light another candle from the flame, you would be using a bit of that heat energy to light the wick on the fresh candle, rather than the room. So the energy loss would be noticed in the room's temperature (though it would be an infinitesimally small loss.

Thing is, the metaphorical equivalent is true. The "happiness" given off by a lone individual would be just increasing the happiness content of an empty room, if not shared.