TORRANCE, CA — July 26, 2002 — In St. Clair, Michigan the heavens appear big, bright and bold, and nowhere more so than at Bob Manning’s home. At dusk the driveway seemingly transforms into a planetarium with glowing stars, planets and moons levitating above the background of concrete. In addition to being a passionate astronomer, Manning is a commercial concrete contractor who wanted to differentiate the driveway of his own home from the mundane cement slabs that he has poured countless times. To accomplish his goal, Manning integrated into the concrete substrate decorative lighting in the forms of celestial objects. “My aim was to have the stars, moons and planets glow at night without overwhelming the surroundings,” he explains. The challenge was finding the right light source. LEDs (light emitting diodes) proved to be the ideal solution due to their resistance to environmental stresses, low power requirements and long operating lives.
In recent years LEDs (Light Emitting Diode) have emerged from the confines of electronic devices to become mainstream lighting tools for architects, automotive designers and industrial lighting professionals alike. LED lamps come in a variety of colors, sizes and standard electrical bases ranging from 3mm “grain-of-wheat” sub-midget flange to 25mm Edison-screw based. Colors available are white, blue, green, red, orange and yellow. LEDs are solid-state devices composed of diode chips made from semiconductor materials that are encased in solid epoxy lenses. Solid-state design makes LEDs impervious
to electrical and mechanical shock, vibration, frequent switching and environmental extremes. LEDs generate light at a specific wavelength (nanometer) when current is applied. The wavelength produced can be in either visible (400 - 700 nanometers) or infrared (830 - 940 nanometers) depending upon the semiconductor compounds used. LEDs are environmentally friendly because they use 80% to 90% less operating power than standard incandescent bulbs, reducing the pollution associated with generating electricity. With an average life span of 100,000-plus hours (11 years), LEDs operate reliably year after year. That’s more than 10-20 times longer than incandescent bulbs!
Longevity of the lamps was of paramount importance to Manning because once the concrete hardened relamping the light fixtures would be impossible. Manning
immediately eliminated incandescent lamps as a solution because, while the up-front costs were minimal, incandescents would require periodic replacing due to their high incidence of failure. Next, Manning considered using fiber optic lighting. With a remote centralized light source from which light is piped down long acrylic strands to multiple objects, fiber optic lighting made relamping a non-issue. However, running fiber optic cables to each embedded object would cost in the neighborhood of $6000, which was just about equal to the amount Manning budgeted for the entire job. Utilizing the Internet, Manning set about researching other lighting alternatives and soon discovered LEDs.
Manning found all the information he needed at the website of LEDtronics, a premier LED lamp manufacturer located in Torrance, California. LEDtronics manufactures thousands of different LED products ranging from discrete surface mount indicators to direct incandescent replacement LED lamps. The LEDtronics website – www.ledtronics.com – offers comprehensive information on LED technologies, products and applications. The site includes tools for cross–referencing incandescent lamps to their LED equivalents, and for calculating the power savings accrued by replacing incandescents with LEDs. LEDtronics
provides specifications online of all their LED products. “That’s what is great about the LEDtronics website, I was able to look at the specs before I placed the order. I saved a few bucks and a lot of time by ordering the right stuff from the start,” says Manning.
He liked what he read: Lamps that provide years of reliable performance. With an average operating life of 11 years (100,000–hours), LEDs fulfilled Manning’s need for a durable lighting solution. Since LEDs are solid–state lights with no filaments or glass tubes to break they could withstand the vibrations from motor vehicles in the driveway, the temperature changes of Michigan’s seasons, and the frequent switching of everyday use. Manning calculated that if the LEDs burned for eight hours per night they would last for the life span of the average concrete driveway – 30–plus years! What further convinced Manning that LEDs were the best solution for his application were the sustained color fidelity and energy efficiency that LEDs provide.
While incandescent bulbs can waste 90 percent and more of the energy they received in the generation of heat and in light blocked by lenses or filters, LEDs deliver 100 percent of their energy as light.
Manning purchased 32 Snap–in ½–inch Top Hat Panel Mount LEDs. (LEDtronics part numbers PF50CW1K white and PF50CB1K blue, sixteen of each color)
The LED lamps feature one LED chip, six–inch wire leads and clear lenses. They are rated for incoming voltages of 12/14Volts DC. Built–in current–limited resistors eliminate the need for any circuit modifications. Blue LED lamps emit light at 470 nanometers, produce 3000 millicandela at 20mA and have a 15–degree viewing angle. White lamps produce an 8000K cool–white light, 6000 millicandela at 20mA and have a 20–degree viewing angle.
The diode chips are composed of Silicon Carbide on a Gallium Nitride substrate.
Constructing the luminaries involved some handiwork on Manning’s part. First, he had a local plastics company mill the stars, moons and planets from a clear acrylic polymer. The finished forms measured five inches in diameter by one and one half–inches thick. Manning drilled a 9/16–inch hole in
each form, inserted one LED lamp, and applied silicon to waterproof each connection. The assemblies were then connected to four–inch wire chairs that had been positioned in the underpinning for the concrete bed. Since LEDs are voltage–sensitive, Manning hooked up the electrical circuit to a power supply calibrated to output precisely 13 volts. After testing the LEDs, the concrete was poured and allowed to cure. A few days later, Bob turned on the luminaries. “The end result produced the WOW effect I was hoping for,” says Manning, pleased with the outcome.
Successfully fulfilling Manning’s vision of a driveway that reflects his interests and transcends the typical cement slab relied on the strengths of LED lighting: 100,000–hour operating life, energy efficiency and solid–state design. As Bob Manning’s application demonstrates, that the sky’s the limit for LED technology!
Publish Date: July 26, 2002
