[hdesbois]

Sometimes you'd want just to tell your emitter is a black body and just set the color temperature and power.
Less often, it could be cool to just specify a wavelenght to get a monochromatic light (I agree you won't use this one everyday, but would be a nice option).
HD

[bathsheba]

It would also be very useful if emitters could be invisible.

Or at least not cast shadows.

-Sheba

[Micha]

... or we could set a special type of lighsource like "fluorescent tube A" and Maxwell use the right spectrum.