To be more energy efficient, many people have replaced their incandescent lamps with light emitting diode (LED) bulbs. However, those currently on the market emit a lot of blue light, which has been linked to eye disorders and sleep disturbances. Now researchers report in Applied materials and ACS interfaces have developed a prototype LED that reduces – instead of masking – the blue component, while making colors appear as they do in natural sunlight.
LED bulbs are popular due to their low power consumption, long lifespan, and the ability to turn on and off quickly. Inside the bulb, an LED chip converts electric current into high-energy light, including invisible ultraviolet (UV), purple, or blue wavelengths. A cap placed on the chip contains several phosphors – solid luminescent compounds that convert high-energy light into visible low-energy wavelengths. Each phosphor emits a different color, and these colors combine to produce a broad spectrum white light. Commercial LED bulbs use blue LEDs and yellow-emitting phosphors, which appear as a cold, bright white light similar to daylight. Continued exposure to these blue-tinted lights has been linked to cataract formation, and turning them on at night can disrupt the production of sleep-inducing hormones, such as melatonin, triggering insomnia and fatigue. To create a warmer white LED bulb for nighttime use, previous researchers added phosphors that emit red, but that only masked the blue tint without getting rid of it. So, Jakoah Brgoch and Shruti Hariyani wanted to develop a phosphor that, when used in a purple LED fixture, would give warm white light while avoiding the problematic wavelength range.
As a proof of concept, researchers identified and synthesized a new luminescent crystalline phosphor containing europium ((Na1.92Me0.04) MgPO4F). In thermal stability tests, the emission color of the phosphor was consistent between ambient temperature and the higher operating temperature (301 ° F) of commercial LED lighting. In long term humidity experiments, the compound showed no change in the color or intensity of the light produced. To see how the material might work in a light bulb, the researchers made a prototype device with a purple light LED covered with a silicone cap containing their luminescent blue compound mixed with phosphors emitting red and green. It produced the desired warm, bright white light while minimizing intensity on blue wavelengths unlike commercial LED bulbs. The optical properties of the prototype revealed the color of objects almost as well as natural sunlight, meeting indoor lighting needs, the researchers say, although they add that there is still work to be done before it is not ready for everyday use.
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Material provided by American Chemical Society. Note: Content can be changed for style and length.