This is am extremely simple, basic diffuser for the popular Lumintop FW3A flashlight. The FW3A has a 25.5mm head, and you should be able to scale it up or down accordingly to fit other lights.

I designed this because I was so disappointed with the official diffuser from Lumintop, which just delicately sites on top of the light.

You should be able to print this without supports. I printed it in glow-in-the-dark PLA from Matter Hackers, but you can use any translucent filament. (Disclaimer: MH GitD PLA is somewhat abrasive.) The diffuser is a close fit, but the stand-up base is somewhat loose. The base works fine as-is, but you can scale it down a tiny bit if you want a tighter fight. I might work out a better stand eventually.