It depends on what kind of light you are talking about. Sunlight, for example, is known for sure to be dangerous for humans, since there is conclusive experimental evidence. Note that the dangerous part of the frequency spectrum is not in the visible range.
It is also known through lengthy exposure of humans to the visible spectrum from artificial lighting that this radiation is safe, as long as the intensity is low.
Microwaves have been around much less than the above and, even though I don't know the current status of research in that field, the implications of lengthy exposure cannot be assessed as easily as for visible light.
The statement I would make would therefore be: there is no conclusive evidence that exposure to WiFi microwaves is more dangerous than equal exposure to light.