Here is what I have so far...
There are moves that involve light as purely something that provides illumination. As stated before, we already have aroura beam, mirror shot, doom desire, sunlight, sunny day, spark, flash, etc... They all involve, in some way, providing illumination to the battle. However, we have not addressed another problem.
Dark-type is not solely taking illumination away, it's using cheap-tricks and cheating to get what you want. I've looked over the entire list of moves for dark-type, and there is no move that involves taking illumination away. They are all tricks and forms of cheating that would normally be looked down on, such as taunting(Torment & Taunt), ganging up on someone(Beat Up), stealing their items(Thief), or striking them when they're not looking(Night Slash).
People are looking at Light-type and thinking it's a type for illumination, others look at it and see angels, holiness, and all that is 'good'. Light-type is a really good idea, but it might not be necessary. We already have a type that looks at the altruistic and harmonic views of battling, such as making your foe fall in love with you(Attract), charming your opponent(Charm), asking kindly for their item(Covet), and showing their affection to their trainer by battling as hard as they can(Return). We can might as well have a new type for this, and it will probably come along with another type to balance out the chart in case Light-type tips it off.