Imperatives to reduce building costs, power consumption and electric utility expense; improvements in light-emitting-diode (LED) and battery technology; and increasing interest in using interior and exterior lighting for design purposes are driving innovation in lighting today. These themes come together in solar lighting and without doubt the solar sector will benefit tomorrow from the engineering and architectural work being done in residential and commercial lighting today.
Here are some of the advances that are being made in lighting and what we can expect to see down the road.
Brightness of white LEDs
Recent advances in semiconductors, optics and materials science has led to the development of blue and then white LEDs and rapid increase in their brightness. Where once LEDs were used only as indicator lamps (initially only red), now they are used to project light in many wavelengths, and they have been doubling in light output about every 36 months.
Power consumption is measured in watts, while light output is measured in lumens. By 2009 LED manufacturers were making white LEDs with an output of 100 lumens per inputted watt (termed efficacy) in commercial quantities, far in excess of the 15 lumens per watt that is typical for incandescent lamps and about the same as the efficacy of fluorescents. In early 2010, the research, development and manufacturing firm, Cree Inc., reported output levels of 208 lumens per watt in a lab prototype.
How are LEDs used today?
Bright white LED lamps (individual bulbs) shine where high efficiency is important at low current levels; from 20 to about 250mA in flashlights, solar-powered outdoor lights and bicycle lights. Color LEDs are used for traffic signal lamps and in strings of holiday lights. As higher wattage LEDs are being used (1-3 watts), higher current draws are being specified in these applications. Flashlights with three AAA batteries and a 3W LED draw 750mA of current.
LED lamps are also being used in large arrays for grow lights for indoor horticulture. Grow light panels include red and blue LEDs because red and blue wavelengths are used by plants for photosynthesis. LED grow lights use less power than other types, need no ballasts, and emit much less heat.
Because of the low operating costs of LEDs, there is a high demand for LEDs in high-current-level applications such as interior residential and commercial lighting, and luminaire (light fixture) manufacturers have started to supply this market. However, at high current levels, LEDs emit heat, so they need to be cooled with heat sink fins or fans, which may not be effective in the small enclosed space of a luminaire.
Architects have been warned that luminaire manufacturers’ representations of lumen output in spec sheets are often based on LED lamp specs, which don’t take into account actual performance of LEDs in a luminaire. Light output will be lower, power consumption higher, and lamp longevity shorter. Actual lumen output may be anywhere between 10 and 60% lower than that indicated by the lumen output of the LED chips due to factors like heat buildup, high current and the use of diffusor lenses, and power consumption may be 15 to 100% greater. The misrepresentations by luminaire manufacturers could result in inappropriate selection of LED lighting and unhappy homeowners.
Research is continuing in the use of LEDs in high-current applications.
LED light bulbs
An important high-current application is the replacement light bulb. A high-efficiency light bulb could replace not only incandescents but compact fluorescent lamps (CFLs) as well, saving huge amounts of power used in homes.
LED light bulbs of good quality are now available as replacements for standard screw-in incandescent light bulbs. Osram Sylvania’s and Philips’ brightest replacement bulbs use 12 watts of power, have an efficacy of about 67 lumens per watt and produce about 800 lumens (+/-10%) of light, equivalent to a 60-watt incandescent. (Buyer beware: Some manufacturers label similar LED bulbs as equivalent to 100-watt incandescents, but they exaggerate. A 100-watt incandescent bulb outputs about 1600 lumens of light, and so would its replacement.) Rated life for a 12W LED is 25,000 hours. They are available at retail outlets for around $40. LED light bulbs are not yet commercially available with light output of 1600 lumens (true 100W incandescent equivalent).
LEDs lights are initially expensive but use 80% less electricity and will last 25 times longer than incandescents (but with a loss of 30% of their brightness). Most are labeled as “dimmable” but may require a special dimmer to avoid flickering when dimmed.
Are LED replacement light bulbs ready for prime time? You decide. They tend to be highly directional. As a result they make excellent PAR reflector-type bulbs (floods and spots) and work well in recessed downlight fixtures and tracks in homes, line-voltage façade lights outdoors, and as spots (both large display lights and small showcase lights) in retail stores. But LED lights made to replace standard incandescent bulbs have a spread of about 140 degrees rather than 360-degrees of incandescents, so try them out in your application before you stock up.
Lowering the cost of manufacture of LEDs
Replacement of conventional light bulbs is hampered by the high cost of available products. At $40 per bulb for a quality product, LED bulbs that produce only 800 lumens in a narrow spread will not find a mass market no matter how long they last or how much energy they save.
Why the high cost? Producing a white LED used in a replacement light bulb is a complex and expensive process that depends on a sapphire substrate coupled with a mirror-like reflector. Researchers are working to streamline the process.
In 2008, a Purdue University materials science research team made LED bulbs with metal-coated silicon wafers with a built-in reflective layer of zirconium nitride to reduce the production cost. Perhaps this technique will be commercially viable in a few years.
Bright new lighting applications
Installations of LEDs in municipal street lamps for outdoor illumination are becoming common and may prove to be an important application for large LED lamp arrays. Coupled with solar collectors and PV panels, they promise substantial savings in running cost. Because they are used outdoors and exposed, they don’t suffer the same heat build-up and performance degradation problems encountered with interior luminaires.
Because interior office and store lighting is wired and because their primary need for lighting is during the daytime, solar energy can theoretically be converted to electricity and used immediately without having to be stored in batteries. So-called hybrid solar/wired lighting uses large outdoor collectors that look like very bright satellite dishes to gather sunlight to run wired indoor lights in commercial buildings.
The future of residential lighting also includes the use of nanotechnology to reduce the costs of lighting interiors.
New ideas for solar power
There are many innovative solar lighting uses already here, such as lights for boats and for camping. Lightweight caps are available for water bottles for hikers that incorporate a solar light circuit and are meant to be used at night as camp lights.
The future of solar extends beyond lighting, of course. Thin films are currently replacing crystalline PV panels on building roofs, which reduces installation costs, and some day you may be able to paint your house with an inexpensive photovoltaic material.
Look for increasing solar use in automotive, RV and boating applications. PV panels and efficient batteries could power our mobile computers, radios, cellphones, GPS units, and lights. Could an all-electric car be powered solely by the sun some day? Three solar vehicles are said to be nearing production: from Sun Motor in the US, Reva in India, and Venturi in Monaco.
As technology further improves and component costs fall, engineers, architects and landscape architects are finding new ways to use low-energy LEDs and low-cost solar lighting in residential and commercial applications. Lighting innovation is healthy and strong.