a light meter is everything...you should have one...every DP should have one and know how to use it...i really cant see lighting things without one....
using a monitor to light is really not the answer...you need to know what stops your lights are at and to keep the same ratio and stops within a scene...
how would one set a stop without a meter? how would you know your DOF for the puller without one?? how would you know if you had even light for a walk without one??? and on and on...
everyone thinking of doing camera work should learn how to use a meter...its a simple tool that means so much...and you can learn to use one in no time at all....
and as a side note...all this F4 talk...means nothing...f4 is great for a focus puller, but more lens used in film should be 1.4...so many things a shot around 3 or a third under...but again...that would be up to the look you are going for and the camera you use...what is the best stop for the framerate and lens you have...this is what will determine the stop you will be lighting for...hell if its outside in sunlight it may be an 11 and if it were inside at night it could be wide open at 1.4...even though the lights are at a 2.6...there is now ideal...its all a look