- 1). Count the number of light fixtures in the area you want to calculate lux level. For example, there are four fixtures in the room.
- 2). Check the manufacture's information to get an exact reading of the lumens that each fixture or light source outputs. Add the values to get the total or, if they have the same value, multiple the value by the number of fixtures. For example, a 100W bulb produces 1,400 lumens. If you have four such bulbs, the total output for the room is 4 * 1,400, or 5,600 lumens.
- 3). Divide the total light output from Step 2 by the area of the room in square meters to calculate the lux level. In this example, the room is 20 square meters, so 5,600 / 20 = 280 lux.
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