The functional and the beautiful, the pragmatic and the aesthetic intersect in lighting.
To light a space well, you need to know how much space there is to light, what you want people to pay attention to, what you're going to do in the space, and where you're going to do it. This guides the pragmatic aspects, while décor considerations will shape the aesthetic elements.
But this basic piece—how much light?—can trip up the lighting layman, especially when fancy words get involved. Incandescent lighting used to be measured in watts, the electrical output needed to power the bulb.
With a shift to so many alternative forms of light, the key word for measuring light has changed to "lumens." What's a lumen and how many do you need for spaces essential as the kitchen island, the dining table, and the bathroom vanity?
The answer might be hard to understand without a background in the science of light. Here's the official definition: "a unit of luminous flux in the International System of Units, that is equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions."
Fortunately, you don't have to understand precisely what a lumen is and how it is measured to get your arms around how to use it.
You just have to know how many square feet you're lighting, and if it's the kind of space where being brightly lit is a priority or not. You'll also have to know what to look for when bulb shopping. They've made it really easy on the side of the box.
If all you'd like to know is how many lumens-per-square-foot a particular room should have, use these handy guidelines.
5-10 lumens-per-square-foot for hallways
10-20 lumens-per-square-foot for living rooms and bedrooms.
30-40 lumens-per-square-foot for dining room and for the ambient layer in the kitchen
70-80 lumens-per-square-foot for bathroom and laundry room, as well as for task lighting on kitchen surface areas where you work
Those numbers are useful, but it will take a little light math to figure them out for your space and bring it from basic to brilliant.
Multiply the width by the length of the space you are lighting to get its square footage.
Add up how many lumens are provided by the light sources currently or planned to be in that space.
Divide the number of lumens by the number of square feet.
This gives you the key measurement, lumens per square feet.
So, let's say it is a 20 x 20 ft room, giving us 400 sq ft.
And let's say you have a six-light pendant using 9W LED bulbs that put out 840 lumens each. 840 x 6 = 5,040 lumens.
Dividing the lumens by the square footage, you find you're getting about 13 lumens-per-square-foot (5,040 ÷ 400 = 12.6).
~13 lumens-per-square-foot might work for a mellow bedroom but is not adequate for most spaces. The addition of other light sources and/or an ambient source with more bulbs and thus more lumens will help here.
Here's where it gets tricky: sometimes the lumens information isn't clearly provided up front. You may have to do a quick google. Look at what the bulb type is and how many come with it.
For example, let's say you select an Abrams chandelier, 8825-AGB, from HVL, for your ambient layer of light.
Looking at the Spec Sheet, you see it comes with 10 40W Max 120V E12 Candelabra bulbs.
Google "40W candelabra bulbs lumens," and you will find out these bulbs produce 480 lumens (also sometimes called Brightness).
Multiply that by the number of bulbs in that fixture, and you will have the number of lumens: 10 x 480 = 4,800.
Of course, in this example, you may wish to replace these bulbs in time with LED ones with the same bulb base (E12 candelabra).
The savvy consumer needs to know the meaning of lm/W—lumens-per-watt. If a 60-watt incandescent bulb produces 800 lumens and a new LED bulb produces 840 lumens on only 9 watts, the LED bulb earns a lm/W efficacy score of 93.
As you can see, no one layer of light, such as a chandelier on the ceiling (ambient), a sconce on the wall (accent), or a lamp on a table (task), is going to meet a room's lumens-per-square-foot requirements.
A room that uses all three, complementing the layers and creating a dynamic space, will be the most comfortable, aesthetically pleasing, and practical.
If you would like additional information on how to select the perfect lighting fixtures for your bath or kitchen, please call our showroom at (215) 454-2258 or visit us at 127 S Easton Rd. Glenside, PA 19038.