I've just read some of posts asking and answering questions about light meters, and how to interpret their readings. I think some of them were getting the wrong end of the stick. It is not a simple process, but i will try an explaination..........
There are 2 basic types of reading; INCIDENT and REFLECTIVE.
An incident reading is taken with a lightmeter with a diffuser, a white hemisphere, by pointing the bulb toward the light source to measure how much of it is falling on the subject.
You enter your film speed
If you are shooting at 24 or 25 frames per second your exposure time will be 1/50th of a second.
The mesurement given assumes an 18per cent reflectivity or middle grey (zone v). You can get these grey cards from any photography shop, they are useful for calibrating and as a reference point.
What that means is, say for example the stop reads f5.6, then if you put a grey card where you take the light reading from, and take your spot meter and get a REFLECTIVE light reading it will read F5.6 also.
(If you are serious about learning this stuff then you must read up on the zonal lighting system, it is the basis for understanding how you translate what your eye sees to what the film sees.)
Reflective readings (Taken with a SPOT METER) are where you can really finesse and fine tune your lighting, by manipulating these values by adding light, or taking it away then translating the readings, you can become more creative.
You are literally measuring the light bouncing of something.
Imagine you light two people sitting next to eachother, a black girl sits next a white girl. The light shining of them is the same (INCIDENT LIGHT) but take a spot reading (REFLECTIVE LIGHT) and the value will be higher for the lighter skin tone. How you use this information and how you manipulate the the light is the important thing.
It is a difficult concept to get your head around, but there is no escaping it, once you understand it then you can express yourself, use your eye, your taste, break the rules, create something beautiful, all the while knowing that your image will be captured the way you want it .
Once you master the science then you can begin to master the art.
Anyone can get an image, you point your incident meter at the lens take the reading set your stop and shoot. Theres a little more to it than that, if anyone is interested I can recommend some decent books on the subject. I hope this hasn't been too confusing.