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ELECOSN asked:


LEDs are solid-state semiconductor devices that convert electrical energy directly into light.

Thermal sources of light such as flames and incandescent filaments emit light when heated, either by chemical reaction (flames) or electrical heating (filament lamps). LED “cold” generation of light leads to high efficacy because most of the energy radiates within the visible spectrum.

Other common high efficiency light sources, such as fluorescent lamps and electro luminescent devices, also produce light without much thermal radiation outside the visible spectrum.

Because LEDs are solid-state devices, they can be extremely small and durable; they also provide longer lamp life than other sources.

Light is generated inside the chip, a solid crystal material, when current flows across the junctions of different material compositions.

An LED consists of two elements of processed material called P-type semiconductors and N-type semiconductors. These two elements are placed in direct contact, forming a region called the P-N junction. The composition of the different materials determines the wavelength and therefore the colour of light generated.

LED resembles most other diode types, but there are important differences. The LED has a transparent package, allowing visible or IR energy to pass through. Also, the LED has a large PN-junction area whose shape is tailored to the application. The device shown in Figure 1 is an AlGaInP LED because the semiconductor layers are aluminum (Al), gallium (Ga), indium (In), and phosphate (P).

Main LED materials

The main semiconductor materials used to manufacture LEDs are:

*Indium gallium nitride (InGaN): blue, green and ultraviolet high-brightness LEDs

*Aluminum gallium indium phosphide (AlGaInP): yellow, orange and red high-brightness LEDs

*Aluminum gallium arsenide (AlGaAs): red and infrared LEDs

*Gallium phosphide (GaP): yellow and green LEDs

 

Why LEDs?

LEDs have a range of benefits which is fast making them the best solution for real energy efficient lighting. Over the course of the next few years some aspects are expected to change significantly.

Lifetime

As solid-state light sources, LEDs have a very long lifetime and are generally very robust due to no mechanical or moving parts.

Incandescent bulbs have an expected lifetime of 1k to 5k hours, while good quality LEDs are often quoted of having a lifetime of 50k hours, more than 5 years continuous use. However it is important to to understand that the performance of LEDs degrades over time, and this degradation is strongly affected by factors such as operating current and temperature.

Low maintenance

The long lifetime of LEDs reduces the need to replace failed lamps, and this can lead to significant financial and environmental savings, particularly in maintenance, labour and recycling. This makes LED fixtures useful for installations in inaccessible locations, but if tasks like cleaning the light fixture are required, then the light sources could be replaced at the same time, negating the “low maintenance” advantage.

Efficiency

As a semiconductor device, LEDs are highly efficient. Current device technology is allowing the performance of these to be pushed to limits that exceed that of standard lighting.

The directional nature of light produced by LEDs allows the design of luminaires with higher overall efficiency.

Low power consumption

The low power consumption of LEDs leads to large energy savings that can often drive the installation of LED-based systems. Initial purchase costs start off higher, but can be proven to return the investment cost in a short period of time.

Brightness

Light outputs are constantly being increased and there are several products that have higher lumen output than traditional lighting.

Heat

LEDs do not produce heat in the form of infrared radiation (IR) unlike incandescent bulbs which makes them hot to the touch.

This lack of heat production allows LED fixtures to be used in locations where heating from conventional sources would cause a particular problem e.g. illuminating food, textiles, artifacts, etc.

However, LEDs do produce heat at the semiconductor junction within the device and good thermal management must be employed on high power devices to maintain operation life

Cost

In many applications, LEDs are expensive compared with other light sources, when measured by metrics such as “£-per-lumen”.

LED manufacturers continue to work towards reducing their production costs while at the same time increasing the light output of their devices.

However, the high initial cost of LED-based systems is offset by lower energy consumption, lower maintenance costs and other factors.

The initial cost may seem high, but take into account the electricity usage that is saved, they pay for themselves.

Electricity Cost savings from switching to LED Direct replacement bulbs

10W LED Bulbs Vs 75W halogen bulb running cost comparison

 

Small form-factors

LEDs are very small - typical high-brightness LED chips measure 0.3 mm by 0.3 mm, while high-power devices can be 1 mm x 1 mm or larger. There are many examples where the availability of small, high-brightness devices have enabled significant market advancement. The obvious example is in mobile phone handsets, where blue, green and white LEDs are now used in most models to back light keypads and liquid-crystal display (LCD) screens.

Instantaneous switch-on

LEDs switch on rapidly, even when cold, and this is a particular advantage for certain applications such as vehicle brake lights.

Colour

LEDs are available in a broad range of brilliant, saturated colours (although performance varies across the spectrum), and white devices are also available. Modules containing different colored LEDs (typically red, green and blue, or RGB) can be tuned to a huge range of colours, and easily dimmed. RGB modules provide a much wider gamut of colours than white LEDs or other traditional white light sources, which is a particular advantage in applications such as backlighting liquid-crystal displays (LCD’s).

RGB LEDs and colour mixing

LED characteristics change with time, temperature and current, and from device to device. For RGB LEDs, the performance of different colored devices changes at different rates. This can result in variation of lamp colour and intensity, and poor reproducibility.

LED Vs Halogen

LED Lighting Types

 

Now the LED bulbs are widely applied in household, office, street, shop, park etc for decoration and lightings LED lighting family mainly includes:

1. LED ball lamp

2. LED spot lamp

3. LED ground lamp

4. LED tube light

5. LED rope lamp

6. LED pool lamp

7. LED curtain lamp

8. LED Christmas (festival) lamp

9. LED ceiling lamp

10. LED road light

11. LED Solar light

Etc.

In a word, LED lightings will be the future of lighting, and it will definitely replace the halogen lights in soon future.

Robin Green asked:


Dimmer switches can give a more relaxed feel to your home, and save you energy as well. But with the increasing prevalence of compact fluorescent lights or CFLs, many people are wondering what options they have for using a dimmer with these lights - or whether it saves more electricity to use a regular CFL, or to use incandescent or halogen bulbs on a dimmer switch.

Let’s start by putting to rest some misconceptions people have over the relative energy use of fluorescent, incandescent, and halogen bulbs.

Many homeowners put in halogen bulbs, starting in the 1990’s, on the mistaken idea that these lights are more efficient than incandescent lights. In fact their energy efficiency is pretty much the same as that of incandescents. So don’t think you’re saving energy by using them.

CFLs, meanwhile, are very efficient - it takes about one fourth as much electricity to light up a CFL as to light up an incandescent or halogen lamp with the same light output. They also happen to last about eight times longer than incandescent lights.

So if you are using a dimmer primarily to save power, you might be better off just switching your incandescent or halogen lights to CFLs, and keeping the dimmer switch on full, or going back to a standard on-off switch. That will give you more light for less power.

If you want a more mellow lighting all the time, one way is to put in light bulbs that aren’t as bright. Whether you go down from, for example, a 100 watt incandescent to a 60 watt incandescent bulb, or down from a 100 watt incandescent bulb to an 18 watt CFL, you’ll still get less light and you’ll use less electricity. Of course, the CFL solution will save you much more electricity in the long run.

But chances are you want the best of both worlds: the low running cost and better durability of CFL bulbs, with the flexibility to dim them when you don’t need their full light.

You may have heard that you cannot put a regular CFL on a regular dimmer switch. In fact you can, but it is not recommended, because it can really reduce the life of the bulb. There is no increased risk of explosion or fire from installing a regular CFL on a standard dimmer switch - you’ll only increase the risk of shortened bulb life. And since the higher price of CFL bulbs is offset by the fact that they outlive incandescent bulbs by a ratio of 8 to 1, putting regular CFLs on a standard dimmer destroys that cost advantage.

If you choose to dim CFLs, you have two real options: buy a special dimmer switch that is compatible with CFLs, or buy dimmable CFLs that are designed to work with standard dimmers.

Both choices leave you with the energy-saving advantages of CFLs, as well as the ability to dim those CFLs. But for now at least, dimmable CFLs seem like the more affordable option, because fluorescent-compatible dimmer switches are prohibitively expensive, while the price difference between standard and dimmable compact fluorescents is miniscule.

Let’s consider the total cost for both options, for a fixture with three 60-watt light bulbs. Let’s assume you already have a standard dimmer switch and regular incandescent light bulbs. If you want to upgrade to CFLs, your choices are:

1. Installing three 13-watt standard CFLs at $3 a piece, and a $49 fluorescent dimmer switch. Total cost: $58.

2. Going for three 13-watt dimmable CFLs at $3.50 a piece, and use the existing dimmer. Total cost: $10.50!

As you can tell, using an existing dimmer switch is a more affordable alternative. Since both options use the same amount of energy, in terms of payback period the solution with dimmable compact fluorescent lights is definitely much shorter.

Even if you need to buy a dimmer switch because you don’t have one, it still makes sense to go with a standard switch and dimmable CFLs. You can get a standard dimmer switch for under $10. Even a fashionable one for $25 is more affordable than a fluorescent dimmer at $49. And with the cost gap between standard and dimmable CFLs so small, the only way a fluorescent dimmer switch will be cost competitive is if its price drops substantially, which it probably will over the coming years.

If your only motive for using a dimmer switch with CFLs is to save money, and you don’t already have a regular dimmer switch, I would suggest you stay with basic CFLs and forego the dimmer switch. Use the money you save on the dimmer switch to buy more CFLs for other areas of your house. Dimmer switches resulted in major savings for incandescent or halogen fixtures because the bulbs were so wasteful. For example, my rec room has six 50-watt bulbs on a dimmer switch. By using the dimmer at about half power, we use 150 watts instead of the full 300 watts. Assuming an hour on each day, that would save 150 x 365 watts, or 55 kilowatt hours a year.

But if we were to switch those halogen bulbs to 13-watt dimmable CFLs, we’d save 81 kilowatt hours a year at their full strength. By turning them down to half, we’d only save an extra 13 kilowatt hours a year - that’s about $1.30 worth of electricity. Not really enough to make it worth considering this alternative.

Consumer response to dimmable CFLs has been less than overwhelmingly positive. There were certainly some teething issues with these lights - early burn-out, flashing light, and loud buzzing noises. These problems have been pretty much resolved in the more recent dimmable compact fluorescents. But if there isn’t a strong motivation for you to dim your CFLs, I would recommend sticking with standard compact fluorescents for a year, until the market offers a wider range of choices for dimmable fluorescent lights. Who knows - in a year or two, fluorescent dimmer switches could be as cheap as standard dimmers.

Madison Greene asked:


One of the biggest challenges the human race faces today is finding and using alternative energy sources. The push for means of generating electricity has been around for over 100 years, but when oil and coal-fired generators produced power inexpensively, the world put the search for alternative energy sources on the back burner for a number of years.

We cannot procrastinate any longer, however, as many of the earth’s natural resources, such as oil, are depleting.

A Short History Lesson on Alternative Energy Sources

The need for an alternate energy source was rekindled in the 1970’s with the oil shortage that created lines at gas stations and produced critical shortages throughout the United States. The search for alternate power generation is not limited to finding new ways of powering vehicles, as supplying cheap power for homes and industries is a continuous endeavor. There have been many advances in the search for alternative energy sources, but the price of the power produced still remains too high.

Wind, water and sun are touted as renewable energy resources with claims that once the technology is perfected, making it more cost effective, they can replace the need for oil and natural gas to turn turbines in the generation process. Even geothermal power production is one of the alternate energy sources being researched.

The Source Of The Energy Depends on The Location

For many people the switch to alternative energy sources is a matter of finding the type of alternative power that works the best in their particular geographical location. Persons who live in areas that have limited exposure to the sun for example, may not be too excited about using solar panels to supply power. When the sun goes down for an extended number of days, the town can go dark.

In some of those areas, wind is not a problem as it seems to blow nearly every day. Using wind power to turn turbines to generate electricity can work there, but may not work in other areas that experience less windy conditions. Another of the alternative energy sources, hydropower uses the power of rivers to turn generators, but the cost of the infrastructure to get power to the people from the generator may still be high for long range use.

With the three major alternative energy sources continuing to be researched and advanced, the need for an answer to out problem becomes more evident every time a person receives their electric bill, or fills their car with gas.

The resources that we have left on the planet are running out. Do your part to keep educated on the latest changes in technology and any up to date with the issues at hand to learn what you can do to help solve the energy crisis.