How to Measure Sunlight Coverage in a Room

Using a Light Meter

• 1

  Divide the room into imaginary quarters. Measure the light in each quarter three times a day in the morning, at noon and in mid-afternoon. Position the curtains or shades in their usual way so your reading represent the most common level of available light.

• 2

  Stand in each quarter of the room with your back to the darkest part. Hold the light meter with the receptive pad pointed toward the nearest window. Do not get between the window and the light meter since your reading will be inaccurate.

• 3

  Record the three light measurements taken throughout the day in a notebook. Add the three measurements together. Divide the sum of the three measurements by three to determine the mean, or average, footcandles of light in each quarter of the room.

Measuring With a Camera

• 4

  Divide the room into imaginary quarters as in Step 1 of Section 1. Ask a helper to hold a sheet of white paper in the center of each quarter. Have the helper point the paper toward the nearest window.

• 5

  Stand off to the side with the camera pointed toward the white paper. Hold the lens of the camera 8.5 to 10 inches away from the paper. Don't stand directly between the window and the paper because your body will cast a shadow and give a false reading.

• 6

  Look through the viewfinder. Adjust the shutter speed to 1/60 second and the ISO to 25. Slowly adjust the f-stop, or lens opening, until it is set to the correct exposure. Low-light conditions are indicated by an f-stop of between f/5 and below. Medium-light conditions are indicated by an f-stop of between f/6 and f/10. High-light conditions will read f/11 and above.

• 7

  Repeat steps 1 to 3 three times a day in the morning, at noon and in mid-afternoon and record the f-stop codes. Record the numbers to get a good idea of the overall light level in each quarter of the room.