How To Use A Light Meter
by William Lulow
A light meter is a device for measuring the amount of light on a given subject. It is important to understand the various types of light meters in order to understand how the metering system in today’s digital cameras work.
(From left to right: flash meter, incident meter, spotmeter)
The REFLECTIVE light meter measures the amount of light that is reflected from the subject. It is usually pointed at the subject from the position of the camera. It works fairly well for most conditions, but can be “tricked” by shiny objects within the scene. It is the type of meter incorporated into most cameras.
The INCIDENT light meter measures the amount of light that falls on the subject. The reading is taken from the subject’s position and aimed back at the camera. This is a very dependable method of determining a correct exposure for the subject as a whole. It can even be used for specific points within a scene if used properly. It is also best for determining lighting ratios in a studio setting.
The SPOT meter is a device which also measures reflective light, but only measures about one-degree of the scene. It is excellent for measuring light reflected from a subject at moderate distances. Since its angle of view is so small, it is not fooled by other reflective elements in a scene.
Most good digital cameras these days, have incorporated the attributes of reflected meters. They can measure an overall scene as well as various types of SPOT readings from “center-weighted” settings to actual spot readings. Read your camera’s manual to understand what settings to use for the types of photographs you intend to make.
Most of my concert photographs were made with the use of a SPOT meter so that I could measure accurately the amount of light reflected from the musician’s face. Here is one example:
In order to set up a ratio lighting in a studio, you need to use an incident meter so that you can measure the exact amount of light falling on the subject’s face. Here is an example of a 1:3 ratio with the mainlight twice as bright as the fill-in light:
The reading on the left side of the model’s face was f/8 and the right side was f/5.6.
Here, the fill-in light’s reading was f/4:
This image was achieved by simply moving the fill-in light back four times the distance as the mainlight.
These kinds of results can be obtained by using the light meter and setting your lights to yield various intensities (readable directly in f/stops). You can use the meter in your camera to do this as well, but you need to be close to the subject so that it is not influenced by any other object in the studio except the subject’s face.