# LED FAQ and CHART



## md.apothecary (Nov 7, 2007)

This information was found at 1000bulbs.com but I figured I would repost it here since there has been an upsurgence of those interested in LEDs.

LED FAQ
Q. What does LED stand for? 
A. LED stands for Light Emitting Diode 

Q. Is an LED a bulb? 
A. LEDs do appear to be bulbs, but in fact are not. LEDs are tiny semiconductors encapsulated in plastic which protects their components and helps to focus the light. 

Q. What is the difference between an incandescent bulb and LED? 
A. Incandescent creates light by the use of a filament. When power is applied, the filament glows and generates heat - which in turn produces light. LEDs are just the opposite. LEDs create light through a 'cold process'. When power is applied to semiconductors (usually gallium, asenic and phosphorous), they're stimulated by the movement of electrons, this creating photons. Photons are the light that is visibly seen by humans. 

Q. Do LEDs have a wire filament? 
A. No, LEDs operate using entirely different components. LEDs are diodes - they only allow power to move in one direction. The anode (+) is where the current comes in and the cathode (-) is where the current goes out, much like the positive and negative terminals of a battery. Incandescent bulbs project light in every direction (omni directional) as opposed to LED lights which project light in specified directions (such as 20, 50 and 120 degrees) due to their package design and layout. 

Q. Why do LEDs use such little power? 
A. LEDs donot use a filament where a conductor is heated and light is created. Filament based lighting consumes more power than the light produced. LEDs produce very little amounts of heat and do not use filaments making them far more efficient in consumption and output. 

Q. Do LEDs produce heat? 
A. LEDs produce very little amounts of heat. The heat noticed in some instances is due to on board components and other factors of the circuit. Inc omparison to incandescent, LEDs produce a fraction of the heat. If LEDs are hot to the touch, they are being overpowered due to improper circuitry. 

Q. Can LEDs be damaged if hooked up backwards? 
A. Yes, they can. LEDs are diodes and only allow power to pass in one direction. To ensure that you will get the most life out of our LED devices, we add additional circuits to prevent this from occuring in both AC and DC applications. 

Q. Are LEDs affected by extreme conditions? 
A. LEDs are geared for harsh environmnts. LEDs function from -40F to 180F. There is no delay or required "warm up time" for LEDs to function. 

Q. Do LEDs attract insects? 
A. No they do not. Insects see entirely differrent spectrums of light and are attracted to ultraviolet light. A side note - flowers create "nectar guides", invisible to the human eye and ultraviolet light attracts insects to flowers for reproductive purposes. This is not to say that all bugs aren't attracted to LED lights, but most can't see the light that LEDs produce. 

Q. How long do LEDs last? 
A. LEDs are rated by manufacturers to operate under normal conditions for approximately 10 years or 100,000 hours of continuous use. As LEDs get older, they tend to dim and fade but aren't susceptible to blinking like incandscent or fluorescents. 

Q.LEDs are more expensive thn other lighting options. Why? 
A. LEDs can operate as stand alone devices, but when grouped or clustered they require additional steps to operate properly. LEDs need proper components such as a circuit board, driving components and some cases and housings to endure the elements. LED circuits can be designed rapidly, but to ensure that they operate correctly and for long periods of time they require testing.


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## md.apothecary (Nov 7, 2007)

What is an LED?
Light Emitting Diodes, as the name states - are diodes. A diode is a semi-conductor device that permits current flow in one direction. Semiconductor diodes are a junction of two materials. One material has a surplus of positive charge (holes), and the other a surplus of negative charge (electrons). When you apply a forward voltage, the electrons and holes are brought together. They combine and release light energy - the 'light emitting' part of the name.

Are LED's inherently directional?
No. One way to boost the luminous intensity spec (usually given in candelas of millicandelas) is to focus the beam more tightly. The same light flux, focused into a tighter beam, will give a higher luminous intensity spec. So indicator LEDs with 10 degree beam width are popular in part because they have higher specs compared to the same LED packaged to have a 30 or 70 degree beam width. It's more common to see illumination-grade LEDs rated in lumens, which doesn't take into account the focusing of the beam. Arrays built from narrowly focused LEDs will be narrowly focused; arrays built from other beam distributions will exhibit the beam distribution of their component LEDs. Narrow-beam LEDs and arrays can lose apparent impact when viewed slightly off-axis.

What is an LED driver? 
An LED driver is a self-contained power supply that has outputs matched to the electrical characteristics of your LED or array of LEDs. There are currently no industry standards, so understanding the electrical characteristics of your LED or array is critical in selecting or designing a driver circuit. Drivers should be current-regulated (deliver a consistent current over a range of load voltages). Drivers may also offer dimming by means of pulse width modulation (PWM) circuits. Drivers may have more than one channel for separate control of different LEDs or arrays How do I convert between candelas and lumens? You can't directly convert since they measure different things. The most useful explanation I've found is that lumens measure light output at the source, while candelas measure the light that falls on a surface. As the area of the surface increases, the number of candelas will decrease even as the number of lumens remains constant. Our handy conversion calculator is coming soon. In the meantime, you can use this table to get an approximate conversion from candelas to lumens. Find your LED beam width in degrees, and divide the candelas number in your specs by the cd/lm factor listed for that beam angle to get lumens.

Beam Angle
cd/lm
5°
167.22
10°
41.82
15°
18.60
20°
10.48
25°
6.71
30°
4.67
35°
3.44
40°
2.64
45°
2.09

Can LEDs be dimmed? 
It's useful to think of an LED as a current-driven device. The light output is proportional to the drive currnt over a decent range. Things go a bit odd at the bottom end of the current range, where the LED may flicker or change color. So dimming by reductions in forward current isn't the most useful technique. Instead, pulse width modulation presents a technique to safely dim an LED from 0 - 100% of its' nominal brightness. By pulsing the LED with current, and varying the duty cycle of the current waveform, the LED rapidly transitions between on and off, and the relative times spent give the impression of being dimmed.

How do you get more light out of an LED? 
LEDs are made by a process that deposits the junction materials on a substrate material. One of the limitations of LEDs is that imperfections in the material deposited on the substrate reduce the efficiency. Improvements in the manufacturing process have given us brighter LEDs, as have new junction materials. To a certain extent, you can also make the junction larger to get more light. But you can't extend that very far, mainly due to those imperfections. Their accumulated effect prevents a junction from growing much bigger than a square millimeter. So we won't likely see larger LED junctions without some advance in materials science to overcome that limitation. Since a single LED is a relatively low power device (by comparison with other light sources), constructing LED arrays is attractive.


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## md.apothecary (Nov 7, 2007)

savings chart


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