Buy some diy flashlight kit. There's an entire community of people that build flashlights for fun and hence a ecosystem of parts.

Then put in the strongest 455mm wavelength diode you can find off Digikey that fits the kit parts.

Haha, 455mm! That's 659MHz, which used to be channel 45 for UHF TVs in the US: https://en.m.wikipedia.org/wiki/Television_channel_frequenci... but has it been reallocated to something else like LTE?

https://www.spectrumwiki.com/wiki/display.aspx?f=659000000&l...

*nm, as in nanometers.