Question about Tobii Eye Tracker Eye Tracker 5

I have now heard in several places that the infrared light can be seen and that it is disturbing. Humans don't see infrared, do they? In the product pictures, the part is simply black, no red dots. Is that switched off or can you really see nothing? I have relatively sensitive eyes, so it would be a shame if I ordered it but then couldn't use it. What experiences do you have?