Ultraviolet Rays
noun
The purple outside line is the color spectrum that's outside purple. Those are ultraviolet rays (the lines are the rays).
しがいせん
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
あんたはまずその紫外線恐怖症を克服しなきゃいけないね。
You must first conquer your fear of the ultraviolet rays.