how to calculate needed lightsource

[vonkuttenberg]

i am wondering quite long time about some math. formula about calculating needed ligting source power.

for example i know that i would like to light up a daylight room where will be the keylight 5m from the actor. i am going to use dof adapter with 50/1.8 lense and opened as possible.

how can i calculate if 700W will be enought or if i need some powerfull lighting source for this setup?

thanks a lot

 

[FBAS]

I don't know the exact formula you're looking for, but you definitely need more accurate information than what you gave to calculate anything. You say a "daylight room" - how much daylight? Does it have a glass roof and the sun is shining, or does it have a small window on an overcast day? You say 700W - is that 700W halogen, 700W hmi, 700W fluorescent or 700W LED?

Because, if your room has a small window, it is overcast and you have a 700W hmi, then you have more than enough light from your fixture. If the room has a glass roof on a sunny day and you have a 700W halogen (which needs to be gelled to daylight) then your lamp is nothing more than a mere eyelight.

 

[vonkuttenberg]

thanks for quick reply, that is exactly what i am asking for. the formula will have some data from exposure meter. is there anything like that formula or everybody is ruining his projects before he gets a experience or blindly trust to somebody? i hope there is some way how to count that number and see, ok i need for this setup 1kW halogen or 500W hmi light.