How Optical Illusions Can Build a Better Bulb

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Straight away, this would use 12.5 percent less electricity

At the SciFoo conference last weekend, brain scientist and illusionmeister Steve Macknikelevated a basic principle of energy conservation—turn off the lights when you don’t need them—to a whole new level. He showed how you can turn off the lights in a way that no one will even notice.

Right now, an AC light bulb turns on and off 50 to 60 times a second, or even faster for a modern ballasted bulb. If you could stretch out the off intervals, you’d save electricity. And if you could do it cleverly, taking the response of the human eye into account, the flickering would not only be imperceptible, but the quality of light might actually improve. “We’re taking advantage of the dynamics of the visual system,” Macknik says.

So far, most efforts to create greener bulbs have focused on the spectrum of light. Incandescent bulbs have long spectral tails, so even at their best, only about a tenth of their energy goes into useful illumination; most gets squandered as infrared radiation. (You can use this handy online calculator to see how much energy a glowing filament emits over different wavelength ranges.) The three main alternatives—fluorescents, LEDs, and a new technology called electron-stimulated luminescence—all emit light by causing a phosphor to glow at certain wavelengths, lopping off the tail. The downside is that spectral engineering takes a toll on color quality. It took me a long process of trial and error to find a good mix of bulbs for our house; I have a big box in my basement with all the CFLs and LEDs I’ve screwed in and back out again. New York Times columnist Bob Tedeschi recently offered his tips on how to match bulb to room.

Macknik and his colleague Susana Martinez-Conde, who work at the Barrow Neurological Institute in Phoenix and write a column for Scientific American Mind magazine, propose to explore not the spectral but the temporal dimension. The two of them have made a name for themselves coming up with visual illusions, and they think bulbs could exploit these tricks to shed more light with less power.

They start with the famous illusion that two identical gray dots or squares look different when you put them on different backgrounds. They find they can accentuate the difference by flickering the illumination at a certain rate. “You can make something brighter or dimmer if you change the temporal dynamics appropriately,” Macknik says. This result seems simple enough, but he says visual studies are prone to a lot of subtle biases; volunteers’ perception of light and dark can be skewed by the order in which the experimenters present their test scenes. It took years to come up with a controlled experiment that could tease out the optimal flicker rate.

This illusion can work even if you don’t realize the light is flickering. When a light turns off and back on within 20 milliseconds, it looks as if it never went off; retinal cells detect the change, but the stimuli get blurred as the brain processes them—an effect known as flicker fusion. Yet the gray patches still look brighter or dimmer.

To achieve the highest contrast, Macknik says a bulb would turn on for 70 milliseconds, off for 10, and repeat—an 87.5-percent duty cycle. Straight away, this would use 12.5 percent less electricity. You can wring out another 10 percent or so because the enhanced contrast would let you get away with a lower-wattage bulb.