Under LED lights, your clothes can’t get “whiter-than-white”

April 19, 2014
April 19, 2014
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Uh oh.(Flickr/Classic_Films)

LED lightbulbs are incredibly energy efficient (pdf), but they could do a number on your crisp white button-downs: According to a new study led by Kevin Houser, a professor of architectural engineering at Penn State University, the most common type of LED lightbulb renders clothing brighteners—the chemicals in detergents that claim to make your whites whiter—useless.

Unlike bleaches, those detergents don’t actually change the fabric’s color: but they make it look whiter, at least under the lights we’re used to. Optical brighteners are used to make white clothes (and other things, including printer paper and blond highlights) appear whiter. These “fluorescent whitening agents” produce a subtle blue glow under most sources of light, counteracting dingy yellow tones and creating a perception of brightness. They have been engineered over decades to work well under sunlight, fluorescent light, and incandescent light.

But if you are one of the many people making the switch to blue-pumped LEDs, your life (or at least your laundry) might get a little bit dingier. The whiteners only glow under violet and ultraviolet light, which the most common type of LED bulb—the blue-pumped LED—lacks.

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You probably don’t realize it, but your laundry detergent is always ready for a rave.(Wikimedia Commons)

The study compared test subjects’ perception of different levels of fluorescence on white backgrounds (with progressively more optical brighteners) under several lighting conditions. A halogen lamp was used, along with a typical blue-pumped LED bulb and three violet-pumped LEDs. Sure enough, participants saw the more fluorescent objects as whiter with each increase in violet light emission. And when they tried to sort the objects by perceived “whiteness” under the light of a blue-pumped LED, they seemed to guess randomly.

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It’s hard to choose, they’re all so different.(Penn State/Patrick Mansell)

The market for LEDs is expected to increase rapidly in the coming years: A recent projection by the consulting group McKinsey & Company estimated that dropping costs and an increase in bans on incandescent bulbs mean that LEDs will make up 45% of the global general lighting market by 2016, and 69% of the market in 2020 (pdf).

For those moving from incandescent light to a more energy-efficient source, many prefer LEDs to fluorescents. And indeed, research has established that colors are still distinguishable and pleasing to the eye under blue-pumped LEDs, the researchers said. But in a home or business lit with LEDs, you might not see the sparkling white products you’ve grown used to—ranging from paper documents to platinum blond hair to tablecloths. That’s because of a mismatch between the way fluorescent whitening agents were engineered and this new form of lighting.

The researchers offer a solution to this mismatch: If companies producing lightbulbs focus on putting violet light into household LEDs, they suggest, we might end up feeling a lot better about our freshly-laundered gym socks.

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