Make UL lantern out of headlamp?

I've seen people make origami paper lanterns for their lights (you can use wax paper maybe, for some water resistance). You can also cut off a finger of some white rubber/nitrile/latex gloves to use (it's what I use). Or a ping pong ball with a cutout to fit your light.

You have a water bottle, right? Just aim the headlamp into the side of the water bottle.

–B.G.–

Put a little cup of aluminum foil in a corner or at the peak of your tent. Aim the flashlight at it.

Are you aware of this:
It is a crushable lantern shade (0.18 oz) designed to use your headlamp.

Here is the link: http://www.montbell.us/products/disp.php?cat_id=52&p_id=1124462

Buy it from Montbell, or make a version for yourself.

I've used expanded polythene foam sheet & block for all sort of uses, for years, and the white, thin sheet (2-3mm) version makes a good diffuser for a headtorch. Same principle as the MontBell thing.

Salvage from packaging, or laminate flooring underlay.

I think I'll try the wax paper tonight. Might also try using my bowl and see if that works. That Montbell one would be perfect, but not so keen on spending $15 for it, maybe $5.

I use Platypus bottles when on the trail, and have found that I can set my headlamp in the small cavity underneath the bottle. I make sure the light is directed into the bottle and it makes a great diffuser that lights up the campsite well.

You could try using a ping pong ball.

Easy to do for a torch but maybe it can work for you too.
Blu Tack or Velcro could be used to keep it in place if you cannot slide it in.