but from what you say they only detect infared light then?
yeap, IR only. as I said, these sensors are typically used for line following and encoders, not for photovores.
but dont really worry, most lights emit light in the infrared spectrum, too. anything really hot, such as a stove or a lightbulb, emits huge amounts of infrared light.
think of infrared as a color you cant see but your robot can, not something that isnt light at all.