How to Calculate Lighting Needs

how to calculate lighting needs

Recently, you saw the fruits of our organizing labor over at Jo-Lynne’s place. After the pantry, we organized…actually, we created the command center. This week I’m going to share more about her laundry room re-do. I’m so glad her talented hubby agreed to another light fixture. Here’s how I knew we needed more light.

To calculate the lighting wattage needed in any room:

Multiply width of room x length of room x 1.5 = amount of total minimum wattage needed (assuming an eight foot ceiling).

Divide by 60 to get the number of 60-watt equivalent bulbs required.

Then, add up the wattage in each bulb in each fixture to figure out how many light fixtures are needed.

Lighting: It Doesn’t all Count the Same

In a room where people typically sit and linger, we do not consider overhead lighting for this exercise. The table and floor lighting gives a softer, more congenial light.

In a walk-through space, like a laundry or bathroom, mounted and overhead lighting does count.

In an area where we need really good lighting, like over a counter, near a make-up table, or where you do homework, you might need to multiply by 2.5 rather than 1.5.

How to Calculate Lighting Needs

So if my living room is 16×12 with an eight foot ceiling, I need 288 watts total, or 4.8 bulbs that are 60-watt equivalent. Of course, that last part is getting tricky, because the CFL and LED bulbs aren’t measured in watts, but will typically show a wattage equivalent on the package. They are now measured in lumens, or “light output”. I shared what’s going on with the new light bulbs in a past post.

Laundry Room Lighting

For Jo-Lynne’s laundry room, she had a 3-bulb fixture, but only one bulb was working, the shade was dark, and it was the kind of fixture that doesn’t reflect much back into the room.

calculating lighting needs

Her room is 12′ x 5.5′, so she needs a minimum of 99 watts, but with a 9′ ceiling, she needs more, especially given that all the light originates from the ceiling fixtures. 165 watts (at least 3, maybe 4 bulbs) starts to feel adequate.

This is room where you don’t want ambiance. You need light! A simple two-bulb fixture just won’t cut it. So by adding a second two-bulb fixture, we fixed the lighting, and made the room feel nearly twice as big.

The color she had originally was a “low light reflecting value” shade, meaning that it was absorbing more light than the average color, so by painting a color with higher light reflective values, we did more with the light available in the room.

Calculate lighting in a room

This equation is like a neat little parlor trick that you’ll be trying at home, and possibly in your friend’s homes too.

Cute, right? I’ll be sharing more adorable laundry room makeover features from Jo-Lynne’s place later this week. Stay tuned!

2 Responses to How to Calculate Lighting Needs

  1. […] I didn’t realize how crucial good lighting is to a space like this. Darla has a whole mathematical equation for determining how much light one needs in a space, but you know how well math and I get along, right? Here is her post explaining How to Calculate LightingNeeds. […]

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