This next generation blue light could potentially promote or hinder sleep on command

Blue light from LED lamps and consumer electronics can mess with your sleep because it disrupts production of the natural sleep hormone melatonin. Tinted glasses or displays in night mode can mask, but don't remove, a portion of the disruptive wavelengths. But now, researchers report in ACS Omega that they have designed more "human-centric" LEDs that could potentially enhance drowsiness or alertness on command.

Humans have evolved over millennia to be active during the day and to rest at night; we've depended on the sun to regulate our sleep/wake cycle.

But many people today spend a majority of their time indoors, shielded from the sun, so it's harder for them to maintain that optimal 24-hour circadian rhythm.

Exposure to artificial light can worsen this problem because it can decrease secretion of melatonin.

And nighttime exposure to blue light, specifically, is notorious for interfering with melatonin production and therefore sleep.

However, blue light is emitted by LEDs in lamps, computers, TVs, phones and other handheld electronics that people often use at night.

So, Changwook Kim, Young Rag Do and colleagues set out to make a light source that could support natural circadian rhythms, no matter what time of day it is used.

Blue light ranges in wavelength from 380 to 500 nanometers (nm), but not all blue light is created equal.

The wavelengths that suppress melatonin production -- and cause wakefulness -- are in the range of 460 to 500 nm. So, the researchers designed two LEDs that emitted different wavelengths of blue light.

One LED, intended for daytime use, restricted its blue emissions to wavelengths close to 475 nm. The other LED, for evening use, emitted blue wavelengths near 450 nm, outside the range that disturbs sleep.

Then the researchers built these two new LEDs into bulbs. Like conventional bulbs, they produced white light by converting some of the blue light into red and green with the help of phosphors encased in the bulbs.

The new LED bulbs were placed along with conventional LED bulbs in fixtures installed in the ceiling of a windowless room furnished with a desk, treadmill and bed.

Individual male volunteers stayed in the room for a stretch of three days.

A computer controlled which type of LED was turned on or off during their stay; that way, the researchers could compare the impact on melatonin levels of conventional bulbs versus the new daytime and evening bulbs.

Saliva samples from 22 volunteers showed that using the new LEDs increased the participants' nighttime melatonin levels by 12.2% and reduced daytime melatonin by 21.9% compared to consistent conventional LED exposure.

The researchers hope manufacturers of LED lamps and electronic displays can apply these findings to help people increase daytime vitality and work efficiency while also improving nighttime relaxation and sleep quality.

Read more at Science Daily

Displays controlled by flexible fins and liquid droplets more versatile, efficient than LED screens

Flexible displays that can change color, convey information and even send veiled messages via infrared radiation are now possible, thanks to new research from the University of Illinois Urbana-Champaign. Engineers inspired by the morphing skins of animals like chameleons and octopuses have developed capillary-controlled robotic flapping fins to create switchable optical and infrared light multipixel displays that are 1,000 times more energy efficient than light-emitting devices.

The new study led by mechanical science and engineering professor Sameh Tawfick demonstrates how bendable fins and fluids can simultaneously switch between straight or bent and hot and cold by controlling the volume and temperature of tiny fluid-filled pixels. Varying the volume of fluids within the pixels can change the directions in which the flaps flip -- similar to old-fashioned flip clocks -- and varying the temperature allows the pixels to communicate via infrared energy.

The study findings are published in the journal Science Advances.

Tawfick's interest in the interaction of elastic and capillary forces -- or elasto-capillarity -- started as a graduate student, spanned the basic science of hair wetting and led to his research in soft robotic displays at Illinois.

"An everyday example of elasto-capillarity is what happens to our hair when we get in the shower," Tawfick said. "When our hair gets wet, it sticks together and bends or bundles as capillary forces are applied and released when it dries out."

In the lab, the team created small boxes, or pixels, a few millimeters in size, that contain fins made of a flexible polymer that bend when the pixels are filled with fluid and drained using a system of tiny pumps. The pixels can have single or multiple fins and are arranged into arrays that form a display to convey information, Tawfick said.

"We are not limited to cubic pixel boxes, either," Tawfick said. "The fins can be arranged in various orientations to create different images, even along curved surfaces. The control is precise enough to achieve complex motions, like simulating the opening of a flower bloom."

The study reports that another feature of the new displays is the ability to send two simultaneous signals -- one that can be seen with the human eye and another that can only be seen with an infrared camera.

"Because we can control the temperature of these individual droplets, we can display messages that can only be seen using an infrared device," Tawfick said, "Or we can send two different messages at the same time."

However, there are a few limitations to the new displays, Tawfick said.

While building the new devices, the team found that the tiny pumps needed to control the pixel fluids were not commercially available, and the entire device is sensitive to gravity -- meaning that it only works while in a horizontal position.

"Once we turn the display by 90 degrees, the performance is greatly degraded, which is detrimental to applications like billboards and other signs intended for the public," Tawfick said. "The good news is, we know that when liquid droplets become small enough, they become insensitive to gravity, like when you see a rain droplet sticking on your window and it doesn't fall. We have found that if we use fluid droplets that are five times smaller, gravity will no longer be an issue."

The team said that because the science behind gravity's effect on droplets is well understood, it will provide the focal point for their next application of the emerging technology.

Tawfick said he is very excited to see where this technology is headed because it brings a fresh idea to a big market space of large reflective displays. "We have developed a whole new breed of displays that require minimal energy, are scaleable and even flexible enough to be placed onto curved surfaces."

Read more at Science Daily