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Elizabeth James' Blog

By Elizabeth James | Other/Just Looking in 91710

The Lighting Formula: How Much Light Do I Need in Each Room?

Some big-shot interior designers may have you fooled into thinking that creating a lighting scheme for a home is a gift. That there is no underlying formula and that they’ve simply created the perfect lighting because that’s what they do: they design. Fortunately, that’s just not true and there is actually a lighting formula that many interior designers and light specialists employ when designing a lighting scheme and combination of light fixtures for a space.

How to Determine How Much Lighting a Space Needs

Before you can begin picking out table lamps or a new ceiling fixture, you’ll need to determine how much light you need in the space. Fortunately, there is a formula you can use to determine it.

This formula uses basic math, so there’s no worries about messing it up or getting the formula wrong. It should be noted that this formula does not apply only to overhead lighting. It also should include other light fixtures into the lighting scheme, including fixtures for task lighting, accent lighting or ambient lighting.

To begin, you’ll need to determine the square footage of the room. This of course, is the simple mathematic formula of length times width. So if the room is 10 feet by 14 feet, the square footage is obtained by multiplying 10 by 14. 10 by 14 equals 140 square feet.

Using the square footage, you’ll multiply the square footage by 1.5 to find out what wattage is needed to light the room. 1.5 multiplied by 140 equals 210 watts needed to light the entire space.

So say this room is a bedroom. To achieve 210 watts, you can install a 100 or 120 watt bulb into the overhead ceiling light fixture. However, prior to installing this high wattage light bulb into the space, be sure to check the light fixture itself for maximum wattage allowed or contact the manufacturer for more information. You may need to use smaller wattages, such as 60 or 80, so as not to overload the light fixture.

If you are able to install a 100 watt bulb in your ceiling light, you still have 110 watts to account for. In the bedroom you can have 2 table lamps that use 40 watt bulbs, bringing your total room wattage up to 140 watts. That still leaves 70 watts unaccounted for. For those final 70 watts, consider installing some accent or ambient lighting. This could include wall sconces on the opposite side of the wall of the table lamps. If these wall sconces require 40 watt bulbs, this puts you 10 watts over your total wattage for the room.

That being said, remember that you don’t have to be exactly on the dot in terms of wattages. Being slightly over or slightly under by 10 to 15 watts is acceptable, as it’s not always easy to create the perfect, exact wattage when using a combination of different light fixtures in a single room.

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