Common LED Types and Packages

LEDs come in two basic categories: Low power LEDs commonly come in 5 mm size, although they are also available in 3 mm and 8 mm sizes. These are fractional wattage devices, typically 0.1 watt, operate at low current (~20 milliamps) and low voltage (3.2 volts DC), and produce a small amount of light, perhaps 2 to 4 lumens. High power LEDs come in 1-3 watt packages. They are driven at much higher current, typically 350, 700, or 1000 mA, and—with current technology—can produce 40-80 lumens per 1-watt package. High power LEDs come in many different shapes and sizes. Some current products from the leading LED manufacturers are shown below.		Structure of a 5mm type LED. Source: Lumileds™ Structure of a high-brightness LED. Source: Lumileds™

Cree® XLamp 7090

Philips Lumileds Luxeon® K2 Emitter

Osram® OSTAR Lighting

Luminous Efficacy

Energy efficiency of light sources is typically measured in lumens per watt (lm/W), meaning the amount of light produced for each watt of electricity consumed by the light source. This is known as luminous efficacy. DOE's long-term research and development goal calls for white-light LEDs producing 160 lm/W in cost-effective, market-ready systems by 2025. In the meantime, how does the luminous efficacy of today's white LEDs compare to traditional light sources? Currently, the most efficacious white LEDs can perform similarly to fluorescent lamps. However, there are several important caveats, as explained below.

Color Quality
The most efficacious LEDs have very high correlated color temperatures (CCTs), often above 5000K, producing a “cold” bluish light. However, warm white LEDs (2600K to 3500K) have improved significantly, now approaching the efficacy of CFLs. In addition to warmer appearance, LED color rendering is also improving: leading warm white LEDs are now available with color rendering index (CRI) of 80, equivalent to CFLs.

Driver Losses
Fluorescent and high-intensity discharge (HID) light sources cannot function without a ballast, which provides a starting voltage and limits electrical current to the lamp. LEDs also require supplementary electronics, usually called drivers. The driver converts line power to the appropriate voltage (typically between 2 and 4 volts DC for high-brightness LEDs) and current (generally 200-1000 milliamps or mA), and may also include dimming and/or color correction controls.

Currently available LED drivers are typically about 85% efficient. So LED efficacy should be discounted by 15% to account for the driver. For a rough comparison, the range of luminous efficacies for traditional and LED sources, including ballast and driver losses as applicable, are shown below.

Light Source	Typical Luminous Efficacy Range in lm/W
	(varies depending on wattage and lamp type)
Incandescent (no ballast)	10-18
Halogen (no ballast)	15-20
Compact fluorescent (CFL) (incl. ballast)	35-60
Linear fluorescent (incl. ballast)	50-100
Metal halide (incl. ballast)	50-90
Cool white LED 5000K (incl. driver)	47-64*
Warm white LED 3300K (incl. driver)	25-44*

* As of October 2007.


Thermal Effects
The luminous flux figures cited by LED manufacturers are based on an LED junction temperature (Tj) of 25°C. LEDs are tested during manufacturing under conditions that differ from actual operation in a fixture or system. In general, luminous flux is measured under instantaneous operation (perhaps a 20 millisecond pulse) in open air. Tj will always be higher when operated under constant current in a fixture or system. LEDs in a well-designed luminaire with adequate heat sinking will produce 10%-15% less light than indicated by the “typical luminous flux” rating.

LED Lighting

Durable solid-state light that is more compact and durable than incandescents

Summary

A Light Emitting Diode (LED) is a semiconductor device which converts electricity into light. LED lighting has been around since the 1960s, but is just now beginning to appear in the residential market for space lighting. At first white LEDs were only possible by "rainbow" groups of three LEDs -- red, green, and blue -- by controlling the current to each to yield an overall white light. This changed in 1993 when Nichia created a blue indium gallium chip with a phosphor coating that is used to create the wave shift necessary to emit white light from a single diode. This process is much less expensive for the amount of light generated.

Each diode is about 1/4 inch in diameter and uses about ten milliamps to operate at about a tenth of a watt. LEDs are small in size, but can be grouped together for higher intensity applications. LED fixtures require a driver which is analogous to the ballast in fluorescent fixtures. The drivers are typically built into the fixture (like fluorescent ballasts) or they are a plug transformer for portable (plug-in) fixtures. The plug-in transformers allow the fixture to run on standard 120 volt alternating current (AC), with a modest (about 15 to 20 percent) power loss.

The efficacy of a typical residential application LED is approximately 20 lumens per watt (LPW), though efficacies of up to 100 LPW have been created in laboratory settings. Incandescent bulbs have an efficacy of about 15 LPW and ENERGY STAR® qualified compact fluorescents are about 60 LPW, depending on the wattage and lamp type. Some manufacturers claim efficacies much higher than 20 LPW; make sure to examine system efficacy, which accounts for the power use of all components. In December 2006, the U.S. Department of Energy studied the efficacy of four luminaries. All four fell short of the manufacturers’ claims; the study implies that manufacturers are relying on measurements of how much light an isolated LED produces, rather than how much light an LED luminaire actually delivers.

LEDs are better at placing light in a single direction than incandescent or fluorescent bulbs. Because of their directional output, they have unique design features that can be exploited by clever designs. LED strip lights can be installed under counters, in hallways, and in staircases; concentrated arrays can be used for room lighting. Waterproof, outdoor fixtures are also available. Some manufacturers consider applications such as gardens, walkways, and decorative fixtures outside garage doors to be the most cost-efficient.

LED lights are more rugged and damage-resistant than compact fluorescents and incandescent bulbs. LED lights don't flicker. They are very heat sensitive; excessive heat or inappropriate applications dramatically reduce both light output and lifetime. Uses include:

• Task and reading lamps
• Linear strip lighting (under kitchen cabinets)
• Recessed lighting/ceiling cans
• Porch/outdoor/landscaping lighting
• Art lighting
  
• Night lights
  
• Stair and walkway lighting
  
• Pendants and overhead
  
• Retrofit bulbs for lamps

Definitions and Terms

Term	Definition	Units	How to interpret
Color Temperature	Color of light	Kelvin (K)	Sunlight at sunrise is 1800K 100W Incandescent light bulb is 2850K Overcast Sky is 6500K
Color Rendering Index (CRI)	Light’s effect on color	Scale of 0 to 100 with sunlight at 100	The higher the number, the more “true” the color will look in that light
Brightness	The intensity of the light.	Lumens	The higher the lumens, the brighter the light
Power	Amount of electrical energy consumed	Watts	Lower the watts, the lower the energy consumed
Efficacy	The efficiency of the bulb to convert electricity into light	Lumens per Watt	More efficient bulbs provide more light using less energy

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PATH Attributes

	Individual LEDs are considerably more efficient; however, the lamp or fixture design is reduced by the driver and electronics. In addition, LEDs do not produce heat like incandescent bulbs.
	LEDs last considerably longer than incandescent or fluorescent lighting. LEDs don't typically burn out like traditional lighting, but rather gradually decrease in light output. Their "useful life" is defined by the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) as the time it takes until 70% of initial light output is reached, often 50,000 hours. They are resistant to thermal and vibrational shocks and perform well when subjected to frequent on-off cycling.

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Ease of Implementation

No additional tools or training are required for installation of LED fixtures.

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Initial Cost

The biggest limitation to LED for common residential use is the cost of manufacturing due to still-limited production runs. Manufacturers claim production will increase considerably in the near future, further lowering prices. Currently, there is a limited number of LED fixture manufactures, but this is changing. Retrofit bulbs range from $25 to $60 for night lights and small lamps.

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Operational Cost

The cost savings of LEDs can be found in smaller wattage lamps or for applications that take advantage of their longevity, such as difficult to reach places. They are also advantageous for dimmable fixtures, since dimmable fluorescents are expensive.

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Installation

The small size of LED lights encourages a variety of design options. White LED lamps are available with Edison (screw-in type) bases to retrofit existing fixtures. There are LED strips that can be used under cabinets. In addition, outdoor landscaping fixtures are available.

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Benefits/Costs

LED lamps have many advantages over traditional lighting methods. These include:

• Low energy consumption – retrofit bulbs range from 0.83 to 7.3 Watts
• Long service life – LED bulbs can last up to 50,000 hours
• Durable – LED bulbs are resistant to thermal and vibrational shocks and turn on instantly from -40C° to 185C°, making them ideal for applications subject to frequent on-off cycling, such as garages and basements
• Directional distribution of light – good for interior task lighting
• No infrared or ultraviolet radiation – excellent for outdoor use because UV light attracts bugs
• Safety and environmentally conscious – LEDs contain no mercury and remain cool to the touch
• Fully dimmable – LEDs do not change their color tint when dimmed unlike incandescent lamps that turn yellow
• No frequency interference – no ballast to interfere with radio and television signals
• Range of color – LEDs can be manufactured produce all colors of the spectrum without filters, they can also produce white light in a variety of color temperatures

There are some current disadvantages to LED lighting:

• LEDs are currently more expensive than more conventional lighting technologies, and may be hard to locate
• LED are very heat sensitive. Excessive heat or inappropriate applications dramatically reduce both light output and lifespan
• LEDs typically cast light in one direction at a narrow angle compared to incandescent or fluorescent lamps so lenses or reflectors are needed in fixtures to broaden the beam (if desired)

Big LED Breakthrough at Purdue University Could Change the World

by Michael Graham Richard, Gatineau, Canada on 07.22.08

Better, Cheaper LEDs
The incandescent lightbulb that wastes 90% of the electricity as heat is dying, we all know that. But a new breakthrough in solid state lighting might also kill compact fluorescent lightbulbs (CFLs) faster than some expected. Scientists at Purdue University have figured out how to manufacture LED solid-state lights on regular metal-coated silicon wafers (more details below). What this means is: much lower costs.

10% Reduction in Total Electricity Use
And since about 1/3 of U.S. electricity is used to produce light, this is major. "If you replaced existing lighting with solid-state lighting, following some reasonable estimates for the penetration of that technology based on economics and other factors, it could reduce the amount of energy we consume for lighting by about one-third. That represents a 10 percent reduction of electricity consumption and a comparable reduction of related carbon emissions," said Timothy D. Sands, professor of Materials Engineering and Electrical and Computer Engineering states at Purdue.

Old LEDs vs. New LEDs
What makes traditional LEDs so expensive is that the light-emitting layer of an LED light is a gallium nitride crystal and it needs to be treated in various ways with expensive materials.

Dailytech:

In sapphire based LEDs, used for green or blue lighting, mirror-like reflectors are need to reflect and resend emitted light, increasing the efficiency. Typically, this layer is extremely expensive to produce, part of the reason the current generation of LED lighting costs so much,costing at least 20 times more than conventional incandescent and fluorescent bulbs. Also, the LEDs are built on sapphire crystals, which provide the color, but are extremely expensive.

But the new LEDs can be made using standard silicon wafers and already existing, less expensive, processes. This would make them competitive with incandescent and CFLs.

The new techniques yield a crystalline structure aligned to the crystalline silicon. This means that the LEDs are less prone to defects and will perform more efficiently [...] silicon dissipates heat more effectively than sapphires. This will reduce damage during operation and lead to longer lifetimes and more reliability..

We might soon have to get used to changing lightbulbs every other decade.

LEDs that are currently available convert electricity to light with an efficiency of 47 to 64%. It is predicted that LED produced with Purdue's process would have an efficiency in the high-end of that range, compared to about 10% for incandescent.

LED Street Lights are Coming

by Michael Graham Richard, Gatineau, Canada on 05.28.08

New Foothold for LED Lights
Dusseldorf, Germany, has 17,000 gas street lamps. The city's power utility has decided to replace 10,000 of them with LED street lights, but that hasn't happened yet. So far, only about 25 of them have been installed.

Of course, LED are still kind of expensive, so there's a capital cost. But once they are in place, their operating costs are lower and they can last for a very long time. Another benefit is that you can direct light much more easily, so you can avoid sending light in all directions (people with a street light across the street from their bedroom window will understand...). The first bump in the road for LED street lights was that some people thought their white light was too cold compared to the red-ish glow of the old lamps, but that can easily be fixed by using colored LEDs. ::Replacing gas lamps with LEDs

10 Ways to Go Green and Save Green

How can we live lightly on the Earth and save money at the same time? Staff members at the Worldwatch Institute, a global environmental organization, share ideas on how to GO GREEN and SAVE GREEN at home and at work.

Climate change is in the news. It seems like everyone's "going green." We're glad you want to take action, too. Luckily, many of the steps we can take to stop climate change can make our lives better. Our grandchildren-and their children-will thank us for living more sustainably. Let's start now.

We've partnered with the Million Car Carbon Campaign to help you find ways to save energy and reduce your carbon footprint. This campaign is uniting conscious consumers around the world to prevent the emissions-equivalent of 1 million cars from entering the atmosphere each year.

Keep reading for 10 simple things you can do today to help reduce your environmental impact, save money, and live a happier, healthier life.

1. Save energy to save money.

   
   Armistead Booker/flickr
   • Set your thermostat a few degrees lower in the winter and a few degrees higher in the summer to save on heating and cooling costs.
   • Install compact fluorescent light bulbs (CFLs) when your older incandescent bulbs burn out.
   • Unplug appliances when you're not using them. Or, use a "smart" power strip that senses when appliances are off and cuts "phantom" or "vampire" energy use.
   • Wash clothes in cold water whenever possible. As much as 85 percent of the energy used to machine-wash clothes goes to heating the water.
   • Use a drying rack or clothesline to save the energy otherwise used during machine drying. If you must use a dryer, consider adding dryer balls to cut drying time.

2. Save water to save money.

   • Take shorter showers to reduce water use. This will lower your water and heating bills too.
   • Install a low-flow showerhead. They don't cost much, and the water and energy savings can quickly pay back your investment.
   • Make sure you have a faucet aerator on each faucet. These inexpensive appliances conserve heat and water, while keeping water pressure high.
   • Plant drought-tolerant native plants in your garden. Many plants need minimal watering. Find out which occur naturally in your area.

3. Less gas = more money (and better health!).

   
   richardmasoner/flickr
   • Walk or bike to work. This saves on gas and parking costs while improving your cardiovascular health and reducing your risk of obesity.
   • Consider telecommuting if you live far from your work. Or move closer. Even if this means paying more rent, it could save you money in the long term.
   • Lobby your local government to increase spending on sidewalks and bike lanes. With little cost, these improvements can pay huge dividends in bettering your health and reducing traffic.

4. Eat smart.

   • If you eat meat, add one meatless meal a week. Meat costs a lot at the store-and it's even more expensive when you consider the related environmental and health costs.
   • Buy locally raised, humane, and organic meat, eggs, and dairy whenever you can. Purchasing from local farmers keeps money in the local economy.
   • Watch videos about why local food and sustainable seafood are so great.
   • Whatever your diet, eat low on the food chain [pdf]. This is especially true for seafood.

5. Skip the bottled water.

   • Use a water filter to purify tap water instead of buying bottled water. Not only is bottled water expensive, but it generates large amounts of container waste.
   • Bring a reusable water bottle, preferably aluminum rather than plastic, with you when traveling or at work.
   • Check out this short article for the latest on bottled water trends.

6. Think before you buy.

   
   Michael Reinhart/flickr
   • Go online to find new or gently used secondhand products. Whether you've just moved or are looking to redecorate, consider a service like craigslist or FreeSharing to track down furniture, appliances, and other items cheaply or for free.
   • Check out garage sales, thrift stores, and consignment shops for clothing and other everyday items.
   • When making purchases, make sure you know what's "Good Stuff" and what isn't.
   • Watch a video about what happens when you buy things. Your purchases have a real impact, for better or worse.

7. Borrow instead of buying.

   • Borrow from libraries instead of buying personal books and movies. This saves money, not to mention the ink and paper that goes into printing new books.
   • Share power tools and other appliances. Get to know your neighbors while cutting down on the number of things cluttering your closet or garage.

8. Buy smart.

   • Buy in bulk. Purchasing food from bulk bins can save money and packaging.
   • Wear clothes that don't need to be dry-cleaned. This saves money and cuts down on toxic chemical use.
   • Invest in high-quality, long-lasting products. You might pay more now, but you'll be happy when you don't have to replace items as frequently (and this means less waste!).

9. Keep electronics out of the trash.

   
   Gaetan Lee/flickr
   • Keep your cell phones, computers, and other electronics as long as possible.
   • Donate or recycle them responsibly when the time comes. E-waste contains mercury and other toxics and is a growing environmental problem.
   • Recycle your cell phone.
   • Ask your local government to set up an electronics recycling and hazardous waste collection event.

10. Make your own cleaning supplies.

    • The big secret: you can make very effective, non-toxic cleaning products whenever you need them. All you need are a few simple ingredients like baking soda, vinegar, lemon, and soap.
    • Making your own cleaning products saves money, time, and packaging-not to mention your indoor air quality.

Next Generation of Cheap Solar Cells

New technology uses cheaper materials instead of expensive silicon crystals. These new solar cells are projected to cost 1/10th of what the more expensive silicon cells cost.