How to Calculate Lighting Requirements

Pose or locate your subject. This will allow you to measure the ambient light falling on the subject and decide whether you will need to add or subtract light to the scene.

Set your desired shutter speed and aperture in the camera or light meter. These settings affect how much light will be necessary for the image to be properly exposed, so they determine the lighting requirements for the image. Aperture also affects the depth of field--how much of the photograph is in focus--and shutter speed affects how motion is captured, so the setting of these controls also depends upon your artistic needs.

Meter the light using a reflected or incident light meter. Reflected metering measures the light which is reflecting off of the subject, and incident metering measures the light falling on to the subject itself. To measure reflected light, aim the light meter at the subject and press the metering button. For incident readings, stand next to the subject and meter the light falling on the subject without facing the subject, then press the metering button.

Add or subtract light to the image to create the correct exposure. This can be done by changing aperture or shutter speed, adding or removing flash or studio lights, reflecting light on to the subject with a reflector or placing a filter over the end of the camera lens to block light. Continue to add or subtract light until the meter shows a balanced reading, then take your photograph.