THAT'S WHAT I'VE BEEN THINKING!!!! Like if Dallan uses a light source to make a barrier then would it be the reason why they consider him strong (Though in terms of physical capabilities it would be all on him) was because they were fighting him on the sun since all of their practice, training and many more. But what will happened if they fight him during the nighttime???
Consider that radiation from the body is a form of light, it doesn't have to be visible light, it's just energy manipulation! So I don't think the sun has effect on his magic.
If it exists, then it has energy on it and it can be extracted with this magic, light probably is just the easier thing to "extract" from and the easiest thing to produce since it's shapeless