How to Calculate Desired Foot Candles

A foot candle is a measure of the intensity of light. The unit is based on the amount of light emitted by a standard candle at a distance of one foot. Lighting levels vary in different rooms of a house. Most people prefer their bedrooms to be less bright than kitchens or living rooms. Once you have decided how bright you want each room of your house to be, you can calculate the number the foot candles necessary to achieve your desired lighting level.

Tape measure
Calculator

Instructions

- 1
  Measure the length and width in feet of each room you wish to light.
- 2
  Multiply the length and width to find the area of the room in square feet. Separate more complex shapes into squares or rectangles to make your calculation easier. For example, an L-shaped room can be split into a square and a rectangle. Perform separate calculations for each part and add the result for the total square footage.
- 3
  Decide how bright you want each room to be. Bedrooms generally require around 15 foot candles, dining rooms usually have around 35 foot candles and bathrooms may have as many as 75 foot candles or more. Choose figures based on your personal preferences.
- 4
  Consult the packaging of the bulbs you wish to use to find their output in lumens. This figure will vary according to whether the bulb is frosted, incandescent or fluorescent. Divide the lumen figure by the square footage of the room to find the number of foot candles it will produce.
- 5
  Adjust the number of bulbs or their lumen output until you reach your desired level of foot candles. For example, if bathroom is 10 feet by 8 feet and is fitted with a bulb emitting 1,760 lumens, the foot candles would be 1,760/80 = 22. If your desired level of foot candles for the room was 65, you would either have to fit a more powerful bulb or three bulbs of that same rating.

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