The Yellowlight Pillow is a pillow obtainable in the store/pillows page in PFS. The pillow is a light yellow pillow with neon around it.
Harnessing the sun's powerful energy to create light is very hard to do. Luckily, you only need a light bulb stuffed inside a pillow to create the Yellowlight Pillow.
I mean, it doesn't give you those harmful UV rays that all these scientist warn us about. And it isn't as hot. Well, unless you leave it on for too long. Then there is a relative chance if it overheating.
And thinking about it, how does a light bulb not break inside a pillow? Especially if you are fighting with it.