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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.