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Difference between revisions of "LED traffic light FAQ"

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** '''What are the common elements that make up an LED?'''
 
** '''What are the common elements that make up an LED?'''
 
** '''How are LEDs made?'''
 
** '''How are LEDs made?'''
 +
Producing an LED starts with a substrate. The substrate is sapphire for InGaN LEDs or gallium arsenide for AlInGaP LEDs. Layers of various materials are then grown on the substrate. These layers are applied under precise pressure and temperature control, and make up the "N layer" or active region and the "P layer". This process is called epitaxial or epi-growth. The brightness, color and intensity of the resulting LED are determined by the quality and consistency of this epigrowth process. After the epigrowth process individual LED chips are defined on the wafer. The wafer is then sawn up in to separate individual LEDs whose exact color and electrical characteristics are then recorded. Finally, the LED is installed in the LED package where wire bonds create the electrical connections. To complete the package, a lens is attached to direct light and silicon is added to protect the chip and fill the air gap between the chip and lens. Each LED is then tested and organized according to color, brightness, and other characteristics. http://www.lumileds.com/technology/manufacturing.cfm#
 +
[Krissy M. Kelly] 12:52pm, 27 September 2007 (EST)
  
 
== '''Efficiency and Lifetime''' ==
 
== '''Efficiency and Lifetime''' ==

Revision as of 16:53, 27 September 2007

Light Emitting Diode (LED) Frequently Asked Questions (FAQ)

Here are a number of frequently asked questions concerning retrofitting street lights with LEDs. (remember to cite your sources and sign/timestamp your answer)

LEDs

  • What does an LED traffic light look like? (picture)

An LED traffic light looks very similar to a regular traffic light. It still gets the job done and is actually brighter. An LED is actually very small and therefore the traffic light is made up of a bunch of smaller lights, this is apparent when you look closely. The color of the light depends on the exact composition inside the bulb. A link to pictures is posted below. http://www.china-led-manufacturer.com/china/led-traffic-light.htm --Susan 14:40, 16 September 2007 (PDT)

  • How does an LED work?
    • What is a diode?

A diode is a component that restricts the directional flow of charge carriers. Also a diode allows an electric current to flow in one direction, but blocks it in the opposite direction. http://en.wikipedia.org/wiki/Diode Here is a link to view a picture of a few types of Diodes. http://en.wikipedia.org/wiki/Image:Diode-photo.JPG Ki Pass 17:16, 18 September 2007 (PDT)

    • What is a p/n junction?

A p/n junction is the connection between two semiconductor type, p-type and n-type. The p/n junctions are said to have fixed characteristics. http://dictionary.reference.com/browse/p-n%20junction --208.103.142.75 18:53, 22 September 2007 (PDT) User: JustineMichelle

    • What does solid state mean?

In a LED light, the term "solid state" refers to the route of conduction through the bulb. There are no gases, filaments, or moving parts in a LED. Instead, the electricity is passed between metal or alloy gaps ("solid state"). This solid state conduction of electricity requires less energy to create the desired light and in turn produces less lost energy via emitted heat.--Hoffster 17:09, 24 September 2007 (PDT)

    • What are the common elements that make up an LED?
    • How are LEDs made?

Producing an LED starts with a substrate. The substrate is sapphire for InGaN LEDs or gallium arsenide for AlInGaP LEDs. Layers of various materials are then grown on the substrate. These layers are applied under precise pressure and temperature control, and make up the "N layer" or active region and the "P layer". This process is called epitaxial or epi-growth. The brightness, color and intensity of the resulting LED are determined by the quality and consistency of this epigrowth process. After the epigrowth process individual LED chips are defined on the wafer. The wafer is then sawn up in to separate individual LEDs whose exact color and electrical characteristics are then recorded. Finally, the LED is installed in the LED package where wire bonds create the electrical connections. To complete the package, a lens is attached to direct light and silicon is added to protect the chip and fill the air gap between the chip and lens. Each LED is then tested and organized according to color, brightness, and other characteristics. http://www.lumileds.com/technology/manufacturing.cfm# [Krissy M. Kelly] 12:52pm, 27 September 2007 (EST)

Efficiency and Lifetime

  • How efficient is an LED compared to a CFL or an incandescent bulb?
Type Efficacy in lm / W
Incandescent 5 - 17
Halogen 16 - 24
CFL 45 -60
FL up to 100
Current generation LED's 26 - 70
Next generation LED's up to 150

For more information see Luminous efficacyDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD.. Current generation LED in this context means: there are many products using this type of LED. Next generation means: there are prototypes available, or the LED is in production but not used much in products.

    • What are the wattages of a normal incandescent light compared to an LED?

Current generation 3W Led's have the light output of a 20W Halogen spot. It is expected that at the end of 2007 there are LED's are on the market with a brightness comparable to a 50W Halogen spot.

  • How long do LED bulbs last? (e.g. what is the estimated lifetime of an LED?)

LEDs have an incredibly long lifespan ranging from 50,000 to 100,000 hours. --Pmthomas99 11:25, 17 September 2007 (PDT)

    • How long do standard incandescent bulbs in street lights last?

A typical incandescent traffic light bulb using 150 watts generally lasts 8000 hours as studies have shown. --Pmthomas99 11:25, 17 September 2007 (PDT)

    • How many incandescent bulbs (and light bulb changes) do you need to last as long as a single LED?

A typical incandescent light bulb last about 1000 hours so if you think about how many hours a LED light bulb has, you'd probably need to change your light bulbs 50 to 100 times whereas a LED light bulb would only need to be changed once. --Pmthomas99 11:25, 17 September 2007 (PDT)

LED Retrofits

  • How do you replace a normal incandescent street light with LEDs?

It is all in the design when it comes to replacing the normal incandescent with LED's. Even though LED lights are small as individuals, they shine brightly and work very efficiently. LED's come in "bulbs" which have the same compatable base as an incandescent bulb. When they replace them, they go up, take off the colored panel, pull the old incandescent lightbulb out and replace it with the array of LEDs. The new street lights will last for years and save money by lower maintenance. (( http://auto.howstuffworks.com/question178.htm)) --Kellygreen06 17:15, 18 September 2007 (PDT)

  • What colors are LEDs available in commercially?

Colors that LEDs are available in are as follows: deep blue (470 nm), blue (490 nm), green (565 nm), yellow (590 nm), amber (610 nm), orange (630 nm), red (660 nm), "super bright" red (650 nm), and deep red (690 nm) http://www.lrc.rpi.edu/programs/transportation/LED/LEDTrafficSignal.asp?section=2.2 --Melinastar22 20:04, 16 September 2007 (PDT)

  • Who manufacturers LEDs for use in traffic lights? (link to web pages)
  • Are any large cities using LED traffic lights? (Name at least 3 with articles -- about half the cities in PA have done it)

In Idaho, the largest county has two cities who have made the switch to LED traffic lights. Article: [1] In Allentown, Pennsylvania, an SEF grant is making the switch from incandescent bulbs to LED's possible. Article: [2] The Boston area in Massachusetts also makes the transformation to save money and energy. Article: [3] --Krd207 12:01, 21 September 2007 (PDT)

Do LEDs save money (show your work)

  • What are the major variables in determining savings?

The true savings from LEDs are found not only in the amount of money saved on electricity, but also money saved on labor and the cost of replacement over time. Labor and replacement cost is substantial when you are looking at a large building with many lights. If you use LEDs, maintenance costs will be much less than if you used traditional incandescent bulbs. The other major variable in savings is the amount of power used compared to the power used for an incandescent bulb. LEDs use only 10-20% of the electricity used by incandescent bulbs. As you can see, LEDs save much more money and energy in the long run. http://www.earthtoys.com/emagazine.php?issue_number=05.08.01&article=chan --Suzann.pomraning 20:33, 24 September 2007 (PDT)

  • How much money is saved over the lifetime for switching out a red light with an LED?
    • What is the payback time and return on investment for red LEDs?
  • How much money is saved over the lifetime for switching out a yellow light with an LED?
    • What is the payback time and return on investment for yellow LEDs?
  • How much money is saved over the lifetime for switching out a green light with an LED?
    • What is the payback time and return on investment green LEDs?
  • How much money is saved over the lifetime for switching out a walk/do not walk sign with an LED?
    • What is the payback time and return on investment for white man LEDs?
    • What is the payback time and return on investment for red hand LEDs?
  • How much money does it cost to make the switch (labor + materials)?

LEDs and the environment

  • If the street lights are running on coal-fired electricity - how much carbon dioxide emissions are prevented by switching to LEDs?
  • How much pollution is prevented switching an average intersection to LEDs? (list all and amounts)

Any other questions

  • Is there any reason not to switch to LEDs?
  • Why hasn't everyone already done this?