Friday, February 26, 2010

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 thenucleus. 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.)

As we saw in the last section, 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.

When current flows across a diode, negative electrons move one way and positive holes moves the other way.
The holes exist at a lower energy level than the free electrons, so when a free electron falls it loses energy.
This energy is emitted in the form of a light photon. The size of the electron’s ‘falls’ determine the energy level of the photon, which determines its color. A bigger fall produces a photon with a higher energy level and therefore a higher light frequency

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.

Wednesday, February 24, 2010

LED Flood Lighting Will Light Up the Night Efficiently

Almost anyone who is familiar with sports that are played outside is familiar with flood lights. Most flood lights are halogen lamps. However, new technology has now allowed LED flood lights to come onto the market. Just as with using any type of LED light, there are numerous benefits for using LED flood lights. Furthermore, there are just as many uses for these lights as there would be for a normal light. Used for settings both indoors and out, the LED flood lights can come in a variety of sizes to meet every need.

There are numerous uses for LED flood lighting. Some of these would be internal. Museums are known to use floodlights to highlight their pieces. There are several advantages to museums using LED lights instead of halogen. First, they are far more cost efficient. This is common amongst all LED lights. They produce a remarkably bright light for a surprisingly low cost. Second, they have a very long life span and are durable. LED lights typically have a lifespan of about 10,000 hours as opposed to halogen lights that only last for about 1,000 hours. Also, while it is still not recommended to do so, an LED bulb can be dropped or mishandled slightly more than a normal bulb that breaks very easily. Another great feature of LED flood lighting that is a benefit to indoor use is the fact that they put out very little heat. Again, using the example of a museum, the benefits are twofold; they not only help save on electricity themselves, but they keep the need for extreme climate control down to a minimum.

Some of the more well known uses for this type of lighting are outdoors. Many people have seen them be used to illuminate sports fields, football (American style) especially. These lights are usually very large and very powerful. Using LED lights instead could save money and the hassle of frequently changing light bulbs. Another use for them is in the construction field. For projects that require illumination at night, flood lights can provide that. LED lights for this use can come in two varieties, ones that are powered by batteries and ones that need to be plugged into a power source. Battery power can usually provide 8 hours of light and are usually rechargeable. Another outdoor use for LED flood lighting lies within the area of hone illumination. There are many people who enjoy illuminating certain aspects of their house, landscaping, and plants with flood lights from the ground up.

While they used to simply be thought of as lights for "big" places, LED flood lights are being brought into the domestic market as well. They offer many advantages over traditional halogen lamps and are becoming more and more popular in many areas.

Monday, February 22, 2010

LED Pool Lights - Illuminate Your Swimming the Cost-Efficient, Natural Way

Pools are a great luxury to have during hot, sweltering, summer days. However, for most people, the ability to enjoy their pool ends at sundown. While moonlit swims can be fun and relaxing, for many, the lack of illumination makes it too risky to enjoy. However, there is a solution now for those who wish to enjoy their pool no matter what time of day it is. This solution would be LED pool lighting. There are several different forms of this type of lighting. That way, it can be implemented for both above ground and in ground pools.

In ground pools have a major advantage as far as lighting capabilities go. There are LED pool lights that can be installed in the sides and bottom of these pools. If the pool has added features such as waterfalls or fountains, LED lights can also be added there for a greater effect. These types of lights are great because they illuminate the entire pool and can even have effects such as changing colors. These can function as mood setting lights.

For above-ground pools and even for in ground pools as well, there is a variety of floating LED pool lights. These can be found at a very reasonable price and do not require any form of installation. They are simply turned on and then placed in the water. There are lights that are very decorative and come in the forms of flowers (such as water lilies). Some LED pool lights are just plain fun looking, such as floating multi-colored orbs that bob around in the water.

There are numerous advantages that are associated with LED pool lighting. First, there is the efficiency of the bulb. LED bulbs are becoming increasingly popular as people seek to cut power consumption. LEDs can put out a surprisingly bright light for as little power as they consume. This means that be they powered through an outlet or by battery, hardly any power will be used when they are turned on. Batteries will last surprisingly long when used in LED pool lights. Another advantage is their durability and longevity. LED bulbs last much longer than regular fluorescent or incandescent bulbs. This is good news for those who have bulbs that are not easily accessed for replacing.

Pool lighting was once considered to be something attainable by only those with the most resources. Today, however, LED pool lighting is being a very popular and attainable option for those who wish to shed some light on their nighttime swims

Thursday, February 11, 2010

Homelights and Toshiba partners on the LED Market (Official)

It is a real opportunity for Homelights to collaborate with a company like Toshiba who is uncontested leader in leading edge electronics products manufacture and a worldwide reputation brand. The technical know-how and the experience of Toshiba related to commercial proficiency and to expertness of Homelights on the LED market will allow both companies to develop considerably their activities.

Wednesday, February 10, 2010

Lyon illuminates European view on LED lighting

European directives, LED standards, color quality and technological innovation were among the main subjects discussed at December’s ForumLED in Lyon, France.

A comprehensive perspective on the solid-state lighting market, mainly from European speakers and exhibitors but with some international participants, was provided at ForumLED, held in Lyon, France in December 2009. Many French companies and organizations are actively involved in solid-state lighting, with energy efficiency high on the agenda.

In France, lighting is becoming the main energy consumer in office buildings, typically consuming 30-50 kWh/m²/yr, according to Christophe Martinsons of CSTB Grenoble. However, the next building code (RT 2012) will require total energy consumption (i.e. for everything, not just lighting) of 50 kWh/m²/yr for non-residential buildings from 2011, and for residential buildings starting in 2013. LEDs are “excellent candidates,” said Martinsons, to reduce energy consumption, particularly in combination with occupancy sensors.

However, energy is not the only consideration. “Building occupants demand good products, well installed, and safe products that are safely installed,” he said, adding that standards will help LED lighting to meet these requirements. “However, Europe has not produced all the standards needed for LED lighting…yet.”

Tuesday, February 9, 2010

What is Color Rendering Index (CRI)?

Color rendering describes how a light source makes the color of an object appear to human eyes and how well subtle variations in color shades are revealed. The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering color when compared to a "reference" light source.

The higher the CRI, the better the color rendering ability. Light sources with a CRI of 85 to 90 are considered good at color rendering. Light sources with a CRI of 90 or higher are excellent at color rendering and should be used for tasks requiring the most accurate color discrimination.

It is important to note that CRI is independent of color temperature (see discussion of color temperature). Examples: A 2700K ("warm") color temperature incandescent light source has a CRI of 100. One 5000K ("daylight") color temperature fluorescent light source has a CRI of 75 and another with the same color temperature has a CRI of 90.

To further understand the physics of color rendering, we need to look at spectral power distribution.

What is spectral power distribution?
The visible part of the electromagnetic spectrum is composed of radiation with wavelengths from approximately 400 to 750 nanometers. The blue part of the visible spectrum is the shorter wavelength and the red part is the longer wavelength with all color gradations in between.

Spectral power distribution graphs show the relative power of wavelengths across the visible spectrum for a given light source. These graphs also reveal the ability of a light source to render all, or, selected colors.

Below see how a typical spectral power distribution graph for daylight.

Notice the strong presence (high relative power) of ALL wavelengths (or the "full color spectrum"). Daylight provides the highest level of color rendering across the spectrum.

Compare the daylight spectral power distribution with that for a particular fluorescent lamp.

The most obvious difference is the generally lower level of relative power compared to daylight - - except for a few spikes. All wavelengths (the "full spectrum) are again present but only certain wavelengths (the spikes) are strongly present. These spikes indicate which parts of the color spectrum will be emphasized in the rendering of color for objects illuminated by the light source. This lamp has a 3000K color temperature and a CRI of 82. It produces a light that is perceived as "warmer" than daylight (3000K vs. 5000K). It's ability to render color across the spectrum is not bad, but certainly much worse than daylight. Notice the deep troughs where the curve almost reaches zero relative power at certain wavelengths.

Here is another fluorescent lamp.

This spectral power distribution looks generally similar to the one above except it shows more power at the blue end of the spectrum and less at the red end. Also, there are no low points in the curve that come close to zero power. This lamp has a 5000K color temperature and a CRI of 98. It produces light that is perceived as bluish white (similar to daylight) and it does an excellent job of rendering colors across the spectrum.

Above are links to linear and compact fluorescent light bulbs from Topbulb that have a CRI of 90 or higher. If you want a high color rendering bulb to produce light perceived as warm white, choose a bulb with a color temperature of 3000K or 3500K. If you want a high color rendering bulb to produce light perceived as white, choose a bulb with a color temperature of 4000K. For a bulb that simulates daylight, choose a color temperature of 5000K or higher.

Monday, February 1, 2010

LED vs. Neon

So, you have looked at plenty of neon sign sites and have probably looked at plenty of LED sign sites by now and you are asking yourself, "What the heck is the difference?" Don't worry, we have all been through it and end up standing there scratching our heads trying to figure out which one to buy. Is one cheaper than the other? Will one last longer? What will other people think about my decision to purchase a neon or LED sign?
Business signage is an important part of your advertising budget and you want to make the right decision. So let’s compare the pros and cons of LED signs versus neon signs. Here is a list of the most important differences:

Price : Generally, LED signs are about 10% less expensive than comparable neon signs. The initial price difference between LED and neon are, therefore, not a significant factor in determining which sign you need for your business. Notice, however, that I said the “initial price.” When you compare the total cost of purchase, maintenance, and operation of LED signs versus neon signs the difference then becomes sizable. We’ll get into more detail about that in a minute.

Space usage : This may not be a big deal for some businesses, but LED signs are 1/3 to 1/5 the thickness of neon signs. Because neon is a little more bulky than LED lights, neon signs tend to be a little wide and taller than its LED counterparts. That usually is not an issue for most business owners hanging signs in their windows or walls. The biggest difference is in depth. An LED sign will only be 1 inch thick whereas a neon sign will most likely be 3-5 inches deep because the the glass tubing must extend away from its backing.

Shipping and installation : Because LED signs and thinner than neon signs, they are also lighter. This makes them easier to ship and install. In fact, our signs come complete with hanging hardware—it’s as easy as hanging a picture.

Brightness : One of the most important features of LED signs is their brightness and clarity. LED technology produces a sign that is very bright yet clear and easy to read from a distance. Neon signs, however, tend to look a little blurry from far away. The clear glow of an LED sign is therefore more appealing to customers and leaves a clear image in their mind as they drive by your business. An excellent and effective form of advertising. And, LED signs are bright and easy to see even in direct sunlight, whereas it can be hard to tell if a neon sign is on or not in the daylight.

Green factor : No, not the color green but green in the environmentally-friendly way. LED signs and lighting use very low power. LED signs use only 10 watts of power—that’s 6-10 times less than comparable neon signs. This low-power usage also makes LED signs safe and cool to the touch. Low-power usage also means you save a lot of money on operating your LED signs. Also, unlike neon, LED signs do not leak toxic gases (like argon and mercury). Neon signs slowly leak their gases out, which is why you sometimes see neon signs flickering or with part of the sign out.

Maintenance : LED signs have virtually no maintenance. There are no gases, no glass tubes, no argon or mercury problems and LED lights don't run out. LED lights are just that...they are small, extremely bright lights (LED stands for light-emitting diodes). LED lights don't have as many issues or problems because its simply little lights. Neon signs will eventually lose all of the neon inside the glass tubes which means you have to replace the gas by taking it to professional neon sign manufacturer or simply buy a new sign. Of course this process takes 10 years or more but eventually it will happen. Another added bonus of LED signs—they are easier to clean than neon signs because there are no tubes to clean off (and those tubes get hot!). LED signs are also high durable and last up to 100,000 hours, even if left on 24/7.

Animation : LED business signs are available in all kinds of flashing and animation options. Because they are made of many separate lights (instead of a continuous glass tube), LED signs offer more animation options than their neon sign counterparts. Also, many are available in your choice of custom colors to match your business’s unique style and personality.

Add it all up and it is easy to see why bright LED signs are the wave of the future. They are a great, eye-catching, budget-friendly way to attract customers. Light up your world the LED way!