Why New Lightbulbs Will Make White T-Shirts Look Bad

LEDs spell the end of a time-honored laundry detergent trick.

LED lightbulbs are incredibly energy efficient, 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.

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.