What Happens to LED Lights in a Vacuum?|
Article - January 12, 2016 By LarsonElectronics.com
What Happens to LED Lights in a Vacuum?
Successful NASA projects revealed that LED lights work in space. In fact, according to Robert Frost, instructor and flight controller in NASA, astronauts use a wide range of lights in space, including incandescent bulbs on space suit helmets and high intensity metal halide spotlights on the International Space Station. Unlike the fixtures on Earth, luminaries designed for space are specially engineered with materials and mechanisms that manage heat efficiently.
Thermal Management Solutions
In space, the transfer of heat is limited. By comparison, on Earth heat is dissipated through the following processes: convection, conduction and radiation. Convection and conduction do not occur in microgravity settings (such as space). Therefore, scientists must rely on a unique heat dissipating process that uses radiation. During space missions, astronauts typically use radiators with large, metallic surface areas that are shaded and pointed away from the sun (some cooling devices are linked to coolant loops).
Previously, NASA invented several methods for managing heat in electronics, including LEDs, in order to keep them cool and operating consistently. In space, astronauts utilize special heat pipes that transfers heat from a hot location to a cooler (remote) area. The device is made up of a tightly sealed tube without air and liquid is added through a partial vacuum. When the liquid comes in contact with the hot surface, it evaporates into a vapor. The cycle, called capillary action, is completed when the vapor comes in contact with a cool surface, where it condenses back into a liquid, releasing the stored heat to the cold surface. One should carefully note that this mechanism does not require any moving parts, and the process can be repeated as often as needed.
This invention was first tested during an experiment titled The Constrained Vapor Bubble in the International Space Station. In the prototype, researchers used a cuvette pipe (quartz glass tube) filled with pentane. Scientists found that microgravity environments made natural convection- that normally takes place on Earth, difficult to facilitate in space. Furthermore, direct radiation is the only way heat pipes manage heat efficiently in such environments.
LED Applications in Space
LED lights are being used by NASA to improve vegetative crop yield rates in space. Initially, the organization teamed up with the University of Wisconsin and the Wisconsin Center for Space
Automation and Robotics to conduct tests on LEDs. NASA scientists concluded that red light with a wavelength range of 630-660 nm, is effective for stem and leaf growth. It is also applicable in seed germination and flowering. Blue light (400-520 nm) contributes to chlorophyll levels inside plants; though this type of light must be regulated closely to prevent overexposure. Far red light (720-740 nm) promotes leaf growth, while reducing conventional flowering times.
A report from Purdue University titled Sole-Source Lighting for Controlled-Environment Agriculture, cited the following advantages of luminaries for such applications: LEDs do not need ballasts, compared to traditional luminaries, such as fluorescents; the lights generate minimal heat with flexible mounting options- preferably close to the plants, and the fixtures are flexible in generating a wide range of wavelengths for optimal plant growth.
NASA is also using LEDs to correct the sleeping patterns of astronauts in space. In an $11.2 million project, the organization plans to outfit part of the International Space Station with LED fixtures. The luminaries will support natural circadian rhythm cycles by emitting blue light in the morning, white light during daytime operations and red light during the evening. The application of blue light is designed to suppress melatonin production in humans, stimulating sunrise and early morning conditions on Earth. On the other hand, red light will be utilized to promote drowsiness through the production of melatonin. The LED lights may also help ease reliance on medication for sleeping, which is common on the spacecraft.