Visible light is not mentioned in the section about targeting when spellcasting (page 183 SR4A, emphasis mine):
A metahuman spellcaster can target anyone or anything she can see directly with her natural vision. Physical cyber- or bio-enhancements paid for with Essence can be used to spot targets, but any technological visual aids that substitute themselves for the character’s own visual senses—cameras, electronic binoculars, Matrix feeds, etc.—cannot be used.
and
The act of choosing a target establishes a mystic link between caster and target. It is through this “targeting link” which the mana of a spell construct is channeled to produce a spell effect. Under the basic Shadowrunrules, such a link requires line of sight or touch
One might solve the contradiction by saying that astral perception is a kind of "natural vision" for the spellcaster. So when not seeing the target with his eyes because he is astrally perceiving, he has still some kind of vision left with astral perception to "see" the target and build the "targeting link".
