Advice on safety for IV 400nm diode

I am working on a project that requires ball so hat with downward or resurfacing black light facing the wearer.

I am located in China and have access to millions of supports, but I am not sure if I am asking for the right thing, or how to know if I receive it. And more importantly if it is safe to shine in someone's face.

The diode options appear to be 5mm, 395-400nm LED. They would attach to a small battery set in the hat. What other information would a supplier need for this application?

As for safety, how do I know if it is too bright or damaging, how do I adjust that for the wearer? Through sizing the battery, or do I need some other controller?

I know these should be something I could figure out but don't know where to start. Thank you in advance.

I've seen something at festivals that sounds similar to what you're after: baseball cap with a couple of UV (395nm) LEDs lighting up the face of the person wearing the cap. The UV from the LED was being used to light up fluorescent face paint. I don't think it's particularly good to have these pointed towards your eyes but it sure did look cool.

I see this is you first post. Welcome!