This is the model of box I used to propose to my girlfriend. 
The box was attached to my sony camera so i could take a video while i was proposing. 
I told my girlfriend that I had built a homemade flash that I wanted to try out by taking a picture of her. 
I put the ring in and at the time of the proposal I pulled the lever down. 
Booom, lots of tears of joy and a very nice effect.

I also uploaded the mount for the canon and a square box only version without the mount.

I'm not a designer so if you can improve this design to actually looks like to a proper flash I'll be happy.

for the light I put 6 led and a lithium battery of 3,7V