Watts the Matter?

a guest post by Lisa J. Reed, Lighting Designer

Watts don’t matter. But if watts don’t matter, what matters? Actually, watts matter more now than ever, so that’s why we have to stop thinking in watts. Watt – er – what??

Let’s start over. In lighting, “watts” are a unit of measurement for the amount of power consumed by a lamp. This doesn’t really indicate how bright a lamp is, just how much electricity it requires to operate. But because of the need for energy conservation, manufacturers are producing products that consume fewer watts while burning just as brightly as their old counterparts. Instead of watts, we need to learn to look for lumens or CBCP, which are actually measurements of light output.

What Watts Used to Mean
From the invention of the electric lamp in the late 1800’s until around the year 2012, incandescent and halogen lamps were the main sources used in residential, retail, hospitality, art museums, conference rooms, churches, restaurants, and pretty much everywhere besides the office. For over 100 years (which spans multiple generations of entire careers) these lamps were specified by the wattage they consumed.

Watts the Matter - incandescent and halogen bulbs

50W MR16 for interior applications up to 12’ ceilings
20W MR16 good for outdoor applications
60W A19 for residential interior lighting
40W A19 for residential outdoor fixtures
75W PAR for floodlights, or 150W if you really need a lot of light…

When Other Lamps Came Along
With the mid-20th century advent of new technologies came new rules of thumb. For some reason we still didn’t make the switch to thinking of lamp lumens when making our selections. It was easier to just learn some new rules.

Watts the Matter - fluorescent and HID bulbs

40W T12 fluorescent for office applications
(followed eventually by 32W T8 fluorescents for offices)
250W high pressure sodium for street lights
400W metal halide lamps for parking lots
1000W metal halide for high mast lighting
1500W metal halide for sports fields

Watts are Meaningless as Indicators of Brightness
Today with LED lamps, the wattage varies so much between manufacturers that these old rules of thumb are out the window, or could only be used as a range:

60W A19 “equivalent” lamps range from 5 to 13 watts per lamp

So, even though it sounds like a case of who’s on first, what’s on second, and I don’t know is on third…Watts are the reason we have to stop thinking in watts. Have you developed any of your own “rules of thumb” for selecting an LED lamp? What are your go-to lamps for specific applications?

Lisa J Reed photo - Lighting Blog

Lisa J. Reed has been attracted to lighting (like a moth to a flame) for 20+ years. She is the Founding Principal at Envision Lighting Design, LLC in St. Louis, where she designs, teaches, and writes about architectural lighting.


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