Energy-efficient lights a threat to sleep?

Charles Czeisler, sleep medicine chief at Brigham and Women’s Hospital, is wary of LEDs, already in phones and laptops. Pat Greenhouse/Globe Staff/Globe Staff

For years, Dr. Charles Czeisler has studied sleep. The chief of the division of sleep medicine at Brigham and Women’s Hospital knows that the invention of the light bulb has profoundly altered human life and biology.

But in a perspective piece published Wednesday in the journal Nature, Czeisler argues that the sleep deficiencies that have become so pervasive among adults and children may be threatened yet again by technological progress: LEDs (light-emitting diodes) that consume far less energy than incandescent bulbs.

The reason Czeisler is wary of LEDs, which are already in our laptops, televisions, and cellphones, is that they are projected to become even more abundant as governments retire the incandescent bulb and shift toward more energy-efficient sources of light. That matters because it isn’t just all artificial light that can reset our body clocks; the exact type of light makes a difference.

Shining light on a subset of light-sensitive cells in the eye, called retinal ganglion cells, can inhibit the release of the sleep-inducing hormone, melatonin. Those cells are particularly sensitive to blue light — and blue LEDs happen to be widely used because it is relatively easy to make the light look white.

“The light is tremendously blue and rich, right at the wavelength that is most powerful at suppressing melatonin and resetting the circadian system,” Czeisler said.

Paradoxically, a shift toward LEDs may present one way to combat the problem, by giving people the ability to tune the color of light in their houses or on their screens — so that we are exposed only to time-appropriate colored light. That could decrease the likelihood that staring at a computer screen right before going to bed would impair sleep. That will only happen if light manufacturers decide to take into account human biology when they develop new products.

In his own house, Czeisler uses a software program called f.lux that tunes the LED displays of computers, shifting them to emit light frequencies that are appropriate for the time of day. He also keeps gadgets and televisions out of the bedroom.