Why will we change all the traffic lights ?

The new traffic lights you are seeing are made out of arrays of light emitting diodes (LEDs). These are tiny, purely electronic lights that are extremely energy efficient and have a very long life.

Each LED is about the size of a pencil eraser, so hundreds of them are used together in an array. The LEDs are replacing the old-style incandescent halogen bulbs rated at between 50 and 150 watts. Most cities in the United States (and around the world) are in the process of replacing their incandescent traffic lights with LED units because of three big advantages:

• LEDs are brighter. The LED arrays fill the entire "hole" and have equal brightness across the entire surface, making them brighter overall.

• LED bulbs last for years, while halogen bulbs last for months. Replacing bulbs costs money for the trucks and people who do the work and it also ties up traffic. Increasing the replacement interval can save a city big dollar.

• LED bulbs save a lot of energy.

The energy savings of LED lights can be huge. Assume that a traffic light uses 100-watt bulbs today. The light is on 24 hours a day, so it uses 2.4 kilowatt-hours per day. If you assume power costs 8 cents per kilowatt-hour, it means that one traffic signal costs about 20 cents a day to operate, or about $73 per year. There are perhaps eight signals per intersection, so that's almost $600 per year in power per intersection. A big city has thousands of intersections, so it can cost millions of dollars just to power all the traffic lights. LED bulbs might consume 15 or 20 watts instead of 100, so the power consumption drops by a factor of five or six. A city can easily save a million dollars a year by replacing all of the bulbs with LED units. These low-energy bulbs also open the possibility of using solar panels instead of running an electrical line, which saves money in remote areas.

SOURCE: HSW

Amazing intelligent outdoor LED lighting !

The Nogloom Light, created by Alexandre Lasnier, ensures you won’t have to endure a moment of gloom. Lasnier, who credits “plants and their relation with the sun,” for inspiration, created a light-sensitive LED lamp that actually does the opposite of most flowers—it unfurls its petals as darkness descends. Embedded within the petals are 12 LED lights and 4 photo sensors. The photo sensors allow the lamp to detect the level of light in the room, and specifically to seek out dark spots, so that it can turn its petals towards the area where light is needed most. Talk about mood lighting! We always knew LED lights were smart, but this design definitely takes the cake!

SOURCE: Elementalled

LED Advantages

While all diodes release light, most don't do it very effectively. In an ordinary diode, the semiconductor material itself ends up absorbing a lot of the light energy. LEDs are specially constructed to release a large number of photons outward. Additionally, they are housed in a plastic bulb that concentrates the light in a particular direction. As you can see in the diagram, most of the light from the diode bounces off the sides of the bulb, traveling on through the rounded end.

LEDs have several advantages over conventional incandescent lamps. For one thing, they don't have a filament that will burn out, so they last much longer. Additionally, their small plastic bulb makes them a lot more durable. They also fit more easily into modern electronic circuits.

But the main advantage is efficiency. In conventional incandescent bulbs, the light-production process involves generating a lot of heat (the filament must be warmed). This is completely wasted energy, unless you're using the lamp as a heater, because a huge portion of the available electricity isn't going toward producing visible light. LEDs generate very little heat, relatively speaking. A much higher percentage of the electrical power is going directly to generating light, which cuts down on the electricity demands considerably.

Up until recently, LEDs were too expensive to use for most lighting applications because they're built around advanced semiconductor material. The price of semiconductor devices has plummeted over the past decade, however, making LEDs a more cost-effective lighting option for a wide range of situations. While they may be more expensive than incandescent lights up front, their lower cost in the long run can make them a better buy. In the future, they will play an even bigger role in the world of technology.

SOURCE: HSW

How Can a Diode Produce Light?

Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called photons, are the most basic units of light.

Photons are released as a result of moving electrons. In an atom, electrons move in orbitals around the nucleus. Electrons in different orbitals have different amounts of energy. Generally speaking, electrons with greater energy move in orbitals farther away from the nucleus.

For an electron to jump from a lower orbital to a higher orbital, something has to boost its energy level. Conversely, an electron releases energy when it drops from a higher orbital to a lower one. This energy is released in the form of a photon. A greater energy drop releases a higher-energy photon, which is characterized by a higher frequency. (Check out How Light Works for a full explanation.)

Free electrons moving across a diode can fall into empty holes from the P-type layer. This involves a drop from the conduction band to a lower orbital, so the electrons release energy in the form of photons. This happens in any diode, but you can only see the photons when the diode is composed of certain material. The atoms in a standard silicon diode, for example, are arranged in such a way that the electron drops a relatively short distance. As a result, the photon's frequency is so low that it is invisible to the human eye -- it is in the infrared portion of the light spectrum. This isn't necessarily a bad thing, of course: Infrared LEDs are ideal for remote controls, among other things.

Visible light-emitting diodes (VLEDs), such as the ones that light up numbers in a digital clock, are made of materials characterized by a wider gap between the conduction band and the lower orbitals. The size of the gap determines the frequency of the photon -- in other words, it determines the color of the light.

SOURCE: howstuffworks

HOW TO CHOOSE YOUR LED LIGHT BULB ?

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 and fittings - LEDs are available in several types of 'pin' sockets or the standard "screw' bases for recessed or track lighting.
• Choose between standard and dimmable bulbs - some LED bulbs now available as dimmable bulbs.

The common styles of LED bulbs available for household use include the following:

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. These bulbs have many uses, such as area lighting for rooms, porches, reading lamps, accent lamps, hallways and low-light applications where lights remain on for extended periods.

Diffused high power bulbs
Designed for standard household use, these bulbs produce light equivalent to a 100-watt incandescent bulb.

Track Lighting
Available in pin base or standard base, LEDs are ideal for track lighting. 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 incandescents, and last 10 times longer than CFLs, the frequency of changing bulbs is greatly reduced.

Recessed Downlight and Spotlight bulbs
LEDs are now available for standard recessed lighting pots and housings. The light output and color quality are similar to incandescent downlights, but draws only about one-fifth of the power. Also, because they are 90% more efficient than incandescents. and last 10 times longer than CFLs, the frequency of changing bulbs is greatly reduced.

Spotlight and Floodlight LEDs
The spotlight LED lacks a dispersing lens, so it appears brighter as its light is directed forward. It runs cool and will last over 50,000 hours due to advanced thermal management design. The floodlight model gives a spread-out dispersed light. Well suited for ceiling lights, outdoor floodlights. retail display lighting, landscape lighting and motion sensors.

SOURCES: eartheasy

Android meets LED bulbs in Google smart-home push

By the end of this year, people will be able to buy an LED light bulb controllable from an Android device, part of Google's move into home automation. At the Google I/O conference, Google demonstrated how Android devices, including tablets and smartphones, can act as a hub for controlling multiple devices in the home, including lighting, appliances, thermostats, and music. Google concocted a lighting demo system with Lighting Sciences Group, which developed an LED bulb that can talk to Android. It uses a new mesh network wireless protocol rather than Wi-Fi, ZigBee, or the other proprietary home automation protocols.


SOURCE: leds-news