Not all light is wholesome and pure. Sometimes it burns, sometimes it can turn you strange and twisted in the shadows cast. The memory of Light is as old as time itself, back unto the moment of creation before which only a handful know. That power is given strength by those who might seat themselves alongside the angels, but it is not its only face.
...ok, where did that come from. Brain please.
Seriously though, if you want a particularly interesting opponent where Light is a major component to the aesthetics of the field, Tome of Radiance is really good for that. Not all that is Radiant is Good. Mammon, after all, covets all that which is beautiful.
Note: if this convinces you at some point to use something from ToR, PM me. As someone who helped build the system, I know pretty much all of its tricks.