Hey Bajee -
There are two possible ways to achieve this effect. One way would be to take a post process material which increases the brightness of objects found behind the mesh and assign it to a basic mesh shape like the flashlight’s triangle and adjust the 3D scale of that mesh to simulate shape change. There are some limitations to this method as you would have to do some complicated variable alignment to check for blocking objects and then either fun a gradient fade to cut the brightness effect or change the Relative Scale 3D.
The other method would require a significant investment into some Programming and is explored quite nicely on this website here, 2d Visibility
Hopefully this will point you in the right direction, if you have further questions about this method please feel free to comment below -
Eric Ketchum