I m going to try and will let you know

Let us know the specication of the flashkight. Interesting to find out!

It depends. I tried and crashed using 2 push bike LED flashlights onto my P3 for a total all up weight increase of 300g. That lesson cost me a new P3 camera.
I switched to 2 Fenix E15 flash lights and it flew like they weren't even there.  Quite bright little beasts for their size.
And just for fun, I mounted a battery powered video light onto one of my 3DR solo's. It hauled a$$ and lit up the sky!
Have fun man. Let us know how u go.

There are many youtube videos showing the Phantom 3 lifting its own body weight.  A payload of 1kg (2.2lb) is about the maximum you would want to try as even this weight severely affects its flight characteristics and stability.  A small torch should not be a problem, in fact some members of the forum use external lights for navigation and visibility.