Saturday, 26 March 2011

Household LED lamps

Lamp sizes and bases

LED bulbs intended to be interchangeable with incandescent lamps are made in standard light bulb shapes, such as an Edison screw base, an MR16 shape bulb with a bi-pin base, or a GU5.3 (Bipin cap) or GU10 (bayonet socket). LED lamps are made in low voltage (usually 12 V halogen-like) varieties, and as replacements for regular AC (e.g. 120 or 240 V AC) lighting. These lamps usually include circuitry to rectify the AC power and to convert the voltage to a level usable by the internal LED elements.

LED light bulbs

Many LED lamps have become available as change for screw-in incandescent or compact fluorescent light bulbs, ranging from low-power 5–40 watt incandescent bulbs, through conventional replacement bulbs for 60 watt incandescent bulbs (typically requiring about 7 watts of power), and as of 2010 a few lamps were available to replace higher wattage bulbs, e.g., a 13-watt LED bulb which is about as bright as a 100W incandescent. (Standard general purpose incandescent bulb emits light at an efficiency of about 14 to 17 lumens/W depending on its size and voltage. The European Union standard, an energy-efficient bulb that claims to be the equivalent of a 60W tungsten bulb must have a minimum light output of 806 lumens.)

Most LED light bulbs are not made to be dimmed (although some models are designed to work with dimmers), and are usually directional. The lamps have declined in cost to between US$30 to $50 each as of 2010. These bulbs are more power-efficient than compact fluorescent bulbs and offer lifespans of 25,000 or more hours, reduced operated at a higher temperature than specified which reduces the carbon emitance. Incandescent bulbs have a typical life of 1,000 hours, compact fluorescents about 8,000 hours. A LED light bulb could last till 25–30 years under normal use. The bulbs maintain output light intensity well over their life-times. Energy Star specifications require the bulbs to typically drop less than 10% after 6000 or more hours of operation, and in the worst case not more than 15%. Led light bulbs are also mercury free, unlike fluorescent lamps. LED lamps are available with a variety of color properties. The higher purchase cost than other types may be more than offset by savings in energy and maintenance.

Several companies offer LED lamps for general lighting purposes. The C. Crane Company introduced a 7-watt replacement for a 60-watt bulb, the "Geobulb", with an efficiency of 59 lumens/W. The company also gave wedge-base lamps for replacement in low voltage fixtures. In the Netherlands, a company called Lemnis Lighting offers a dimmable LED lamp called Pharox. The company Eternleds Inc. offers a led bulb called HydraLux-4 which uses liquid cooling of the LED chips. Philips makes a number of LED lamps which are commercially available in the United States and come with a six year warranty, and a number of smaller producers can be found that sell LED lights that are screw-in replacements for conventional bulbs, for example, the General LED Bulb from Arani
LED tubes in various length

The technology is growing rapidly, and new energy-efficient consumer LED lamps have been announced from three of the lighting industry’s largest producers, Osram Sylvania, Philips, and General Electric, so these listings should be taken as not necessarily representative of what is currently available.
High power LED lamp with GU5.3 fitting and aluminum heat sink, intended to replace halogen reflector lamps.

 Specialty uses

White LED lamps have achieved market dominance in applications where high efficiency is important at low power levels. Some of these applications include solar-powered garden, flashlights or outdoor street lighting, and bicycle lights. Monochromatic (colored) LED lamps are now commercially used for traffic signal lamps, where the ability to emit bright monochromatic light is a desired feature, and in strings of holiday lights.

LED lights have become very popular in agriculture and gardening by 2011. First used by NASA to grow plants in space, LEDs came into use for home and commercial applications for indoor horticulture (aka grow lights). The wavelengths of light emitted from LED lamps have been specifically tailored to supply light in the spectral range needed for chlorophyll absorption in plants, promoting growth while reducing wastage of energy by emitting minimal light at wavelengths that plants do not require. The red and blue wavelengths of the visible light spectrum are used for photosynthesis, so these are the colors almost always used in LED grow light panels. These lights are attractive to indoor growers since they use less power than other types for the same light intensity, need no ballasts, and emit much less heat than HID lamps. The reduction in heat allows time between watering cycles to be extended because the plants transpire less under LED grow lights. Due to this change in growth conditions, users of LEDs are advised not to over-water the plants.

Pioneering mass use

In 2008 Sentry Equipment Corporation in Oconomowoc, Wisconsin, USA, has lighten its new factory interior and exterior almost solely with LEDs. Initial cost was three times more than a traditional mix of incandescent and fluorescent lamps, but the extra cost will be repaid within two years via electricity savings, and the lamps should not need replacing for 20 years. In 2009, the Manapakkam, Chennai office of the Indian IT company iGate spent 3,700,000 Indian rupees (U$80,000) to light 57,000 sq ft (5,300 m2) of office space with LEDs. The firm expects the new lighting to pay for itself fully within 5 years.

LEDs on a big Christmas tree

In 2009 the exceptionally big Christmas tree standing in front of the Turku Cathedral in Finland was hung with 710 LED bulbs, each using 2 watts. It has been calculated that these LED lamps will pay for themselves in three and a half years, even though the lights run for only 48 days per year.
By 2010 mass installations of LED lighting for commercial and public uses were becoming common.

In 2010, on the reconstructed section of Bulevar Kralja Aleksandra (King Aleksandar Boulevard) in Belgrade, Serbia, LED lamps were introduced for new street lighting.
LED lamps have also been used for a number of demonstration projects for outdoor lighting and street lights. The United States Department of Energy has available several reports on the results of many pilot projects for municipal outdoor lighting. Many additional streetlight and municipal outdoor lighting projects have been announced.

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