Bruce Cordell asks at http://community.wizards.com/dndnext/blog/2012/01/18/holy_and_radiant if the ‘radiant’ and ‘holy’ damage types should (poll actually says ‘can’, but conversation at google+ says he really means ‘should’ if it makes more sense) exist in the same game.
I didn’t take part in the poll because I think the poll is poorly worded, but I think the underlying question deserves a response. From my comment there:
It used to be that ‘holy’ was divine power (usually good), while ‘radiant’ would be positive energy, a fundamental building block (literally so) of the universe. One exists because of powerful will, one just exists. They are different things.
True, there is often presented an overlap between them, in that ‘good divine power’ seems to draw on or make use of positive energy… but I don’t see it as a necessary thing. I can imagine an evil god calling on positive energy (radiant power) to create, or damage, something. Similarly, a good god calling on negative energy (‘the merciful, the ender of pain’) isn’t beyond my imagining.
I’d say they are different things, there is just often a correspondence between them.
As far as preference is concerned, I like the division — positive and negative energy is just that — energy. It just is, without the alignment weighting ‘holy’ or ‘unholy’ would give it. I don’t want to require a divine relationship to use it, and conversely I don’t think I want to lose the option of ‘divine power’ for ‘just energy’ anyone can handle.
I see value to having them distinct. In fact, what I would really like to see is multiple energy types that have specific effects. I don’t remember seeing differences in energy effects beyond what defenses work against them, and who is particular vulnerable to them. Fire, cold, electricity… it just depends whether you have red, white, or yellow protection to shield you from them, or if you have the red, white, or yellow vulnerability that causes you to take more damage. That seems kind of weak to me.