The journal PloS ONE has an article submitted by researchers from the University of Torino and The University of Padova in Italy regarding the sensitivity autistic children have to shadows. Neurotypical children tend to use shadows to help recognize objects while observing their world. As such, a shadow can be of help in a learning environment.
The research here recognized a significant measured delay in identifying item by shape and position using shadows. Basically, because the shadow was adding visual "noise", the children took longer to recognize the objects when compared to the neurotypical control group, and in comparison to the same objects without definite or pronounced shadows.
So what does this really mean? Basically, it means when you try to teach your child with autism, you need to make sure you have multiple light sources within the room to remove as much of the shadow as you can. This will reduce the presence of visual "noise", and help the child better engage with the objects around them.
For those who have autistic children that tend to be visually sensitive anyway, this is probably already being managed. For those of us who haven't had a child start going into a meltdown while walking into a badly lit building with flickering florescent lights (which sure bring on migraines for me), this may be something new.
So how do you get multiple light sources? Two lamps can do it, one on each side of the room. Most commercial environments (or industrially built buildings like schools, churches, etc.) will also have multiple light sources. But how many light sources do you have in your house? You may have natural light, you may have a lamp or two. A suggestion that could save some frustration would be to use a glossy or semi-gloss, light-colored paint to help reflect light. More than one lamp or lighting fixture in a room, and generally at opposite sides. There are a lot of potential solutions to help maximize the help for your child.