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LEDs (Light Emitting Diodes)  are small, solid light bulbs which are extremely energy-efficient. Until recently, LEDs were limited to  single-bulb use in applications such as instrument panels, electronics, pen lights and, more recently, strings of indoor and outdoor Christmas lights.

Manufacturers have expanded the application of LEDs by "clustering" the small bulbs. The first clustered bulbs bulbs were used for battery powered items such as flashlights and headlamps. 

Today, LED bulbs are made using as many as 180 bulbs per cluster, and encased in diffuser lenses which spread the light in wider beams. Now available with standard bases which fit common household light fixtures, LEDs are the next generation in home lighting.

The high cost of producing LEDs has been a roadblock to widespread use. 

However, researchers at Purdue University have recently developed a process for using inexpensive silicon wafers to replace the expensive sapphire-based technology. This promises to bring LEDs into competitive pricing with CFLs and incandescents. LEDs may soon become the standard for most lighting needs. 

Benefits of LED lightbulbsLong-lasting - LED bulbs last up to 10 times as long as compact fluorescents, and far longer than typical incandescents. 

Choosing an LED lightbulb Many different models and styles of LED bulbs are emerging in today's marketplace. When choosing a bulb, keep in mind the following: 

• Estimate desired wattage - read the package to choose desired illumination level. For example, a 3W LED is equivalent in output to a 45 W incandescent.

• Choose between warm and cool light - new LED bulbs are available in 'cool' white light, which is ideal for task lighting, and 'warm' light commonly used for accent or small area lighting.

• Standard base or pin base - LEDs are available in several types of 'pin' sockets or the

standard "screw' (Edison) bases for recessed or track lighting.

The common styles of LED bulbs include the following: Recessed/Track bulbs

Available in pin base or standard (Edison) base, LEDs are ideal for track or recessed lighing. LEDs do not contribute to heat buildup in a room because no matter how long they remain on, they do not get hot to the touch. Also, because they are 90% more efficient than

incandescants, the frequency of changing bulbs is greatly reduced. 

Diffused bulbs In this style LED bulb, clusters of LEDs are covered by a dimpled lens which spreads the light out over a wider area. Available in a range of wattage and sizes, these bulbs have many uses, such as area lighting for small rooms, porches, reading lamps, accent lamps, hallways and low-light applications where lights remain on for extended periods. 

Spotlight and Floodlight LEDs The spotlight LED lacks a dispersing lens, so it appears brighter as its light is directed forward. The floodlight model gives a spread-out dispersed light. Well suited for ceiling lights, outdoor floodlights. Retail display lighting, landscape lighting and motion sensors. 

LED Colors 

Red - red is the traditional color for maintaining night vision.

Green - green is now the preferred color for pilots and the military. The green color is also great for retaining night vision, and it doesn’t erase the red markings on maps and charts.

Blue - many people like the blue because it is very easy on the eyes. Blue appears to be a good reading light for elderly eyes. Elderly folks report that they can read under the blue light for hours without eyestrain, compared to severe eyestrain in less than 30 minutes with incandescent lighting.

White - the most popular of the LED colors. It produces a soft white light, without harsh reflection, glare or shadows.

Amber - LED amber bulbs do not attract flying insects, as do ordinary white bulbs. Amber LEDs are used outdoors in areas such as patios and decks where insects flying around lights are a nuisance.

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LED lamps Replacing an incandescent lamp for LED lamps is not quite easy because you can't simply use the power of the lamp. To choose the right LED lamp a little-bit knowledge about the luminous flux (in lumen), luminous intensity (in millicandela) and the radiation angle (in ) are important. 

Radiation angle At a narrower radiation angle the luminous intensity (clarity) becomes larger whereas the luminous flux (quantity of light) doesn't change. For example: A 1000 mcd 30 led lamp radiates just as much light as a 4000 mcd 15 led lamp. The radiation angle has been halved in both width and height multiplying the luminous intensity four times. 

Luminous flux Luminous flux is a measure for the quantity of energy that is transmitted by a light source in all directions. The SI unit of luminous flux is the lumen (lm). e.g. the luminous flux of a 40 Watt light bulb is 450 lm. 

Luminous intensity The luminous intensity of a light source is the density of that flux emitted in a given direction. For lamps this is expressed in millicandela (mcd). 

Convert Millicandelas to Lumen To calculate lumen from millicandelas, take the number of candelas, divide it with the number that belongs to the radiation angle of the lamp.

Example: 590,000 mcd = 590 cd, a lamp with a radiation angle of 40, 590/2,64= approx. 223,48 Lumen.  

Radiation angle To get lumen: divide the millicandela by

5 167,22

10 41,82

15 18,50

20 10,48

25 6.71

30 4,67

35 3,44

40 2,64

45 2,09 

Color temperature The Color temperature can be indicated in Kelvin or Mired (1 million divided by the colour temperature in Kelvin). 

Color temperature Kelvin (K) Mired (M) 

"Warm white" or "Soft white" < 2700 K 370 M

"White", "Bright White", or "Medium White" 2900 - 3000 K 333- 345 M

"Cool white" 4000 K 250 M

"Daylight" > 5000 K 200 M 

Electric lighting burns up to 25% of the average home energy budget.The electricity used over the lifetime of a single incandescent bulb costs 5 to 10 times the original purchase price of the bulb itself.

Compact Fluorescent Lights (CFL) and Light Emitting Diode (LED) bulbs have revolutionized energy-efficient lighting. 

CFLs are simply miniature versions of full-sized fluorescents. They screw into standard lamp sockets, and give off light that looks just like the common incandescent bulbs - not like the fluorescent lighting we associate with factories and schools. 

LEDs are small, solid light bulbs which are extremely energy-efficient. New LED bulbs are grouped in clusters with diffuser lenses which have broadened the applications for LED use in the home. 

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 copyright 2007 @ CENTRE FOR APPLICATION OF RENEWABLE ENERGY