A kawaii cute science pun of a wave of ghosts - a spectral wave! The spectrum of electromagnetic waves in physics can be referred to as spectral waves.
Where to buy online
Direct from us here - see products featuring this design.
Elsewhere online
RedBubble (US)
Threadless (US)
TeePublic (US)
NeatoShop (US)
You can find the design on t-shirts in most stores, but also on other products depending on the store (e.g. hoodies, mugs, stickers, notebooks, phone cases, greeting cards, cushions, socks etc).