Rocket engine testing requires a lot of light since all tests are filmed with high-speed cameras to monitor performance; however, those cameras have to adjust to the bright plume from a firing engine, which would black out the rest of the image. Traditionally, that light has been provided by metal halide bulbs.
When Stennis Space Center officials wanted to try more energy-efficient lighting in the center’s rocket engine test stands, they couldn’t simply go out and buy the latest LED bulbs. Anything that’s going to share a room with a live rocket engine generating half a million pounds of thrust, 120 decibels of vibration, and temperatures in the thousands of degrees by ejecting hot gases at more than a dozen times the speed of sound in a process involving flammable liquids and gases, needs some special engineering.
In 2009, Stennis decided to try LED lighting, which was new at the time but promised significant energy savings. The center issued two Small Business Technology Transfer (STTR) contracts to LED lighting company Energy Focus (Solon, OH). With those contracts, the company developed floodlights able to withstand the hazardous conditions in test stands to illuminate engine testing, as well as general area lighting.
Although LEDs are relatively efficient in that they generate far more light than heat, they do still emit some heat, and the hermetically sealed design necessary in a potentially flammable environment made temperature management the biggest challenge to overcome. “We successfully overcame that by using an array of heat spreaders that contacted the LEDs directly and were able to extract heat properly,” said John Davenport, who was the company’s executive director and chief scientist at the time, and who remains a senior technical advisor to Energy Focus. The key was a thermally conductive aluminum alloy in a configuration that allowed internal conduction and convection to move heat out through a heat sink.
For the floodlights, the company developed highly efficient optical cones that allowed for less stray light when focusing a beam. After completing the project, Energy Focus redesigned its general area lighting for lower cost and put out the LED HazGlobe for hazardous areas as well as explosion-proof globe lights. The floodlight also evolved into a similar commercial product for use in hazardous areas.
Meanwhile, the original eight LED floodlights have been installed in Stennis’ A-1 test stand where engines planned for NASA’s Space Launch System have been tested in recent years, and 16 general area LED lights illuminate the center’s E Complex, which is used for testing developmental rocket engine components. Energy Focus’s LED floodlights produce the same amount of light as their 1,000-watt metal halide predecessors but use less than 300 watts.
LEDs can be tailored to emit light across the visible spectrum, making them more accurate for scientific imaging purposes and safer for human lighting. While a fluorescent bulb needs to be changed every few years, depending on use, Energy Focus became the first company to offer an unqualified 10-year warranty on its lights.
The hazardous area lights are being used in oil rigs, paint spray booths, elevator shafts, grain and steel mills, and munitions areas, among other uses. About 60 percent of Energy Focus’ business is with the military — particularly the Navy — with the rest coming from the commercial market. The company retrofitted approximately 450,000 LED tubes across the fleet and on every surface ship in the Navy. In addition to light energy savings, there are also tangible cooling energy savings. A ship lit with LEDs likely dedicates less fuel to cooling because the lights generate less heat than the old fluorescent technology.
Spinoff is NASA’s annual publication featuring successfully commercialized NASA technology. This commercialization has contributed to the development of products and services in the fields of health and medicine, consumer goods, transportation, public safety, computer technology, and environmental resources.