What does LED mean? It stands for Light Emitting Diode. For writing convenience, we will take the first letter of the words – L.E.D. to form the abbreviation of light emitting diode. It is a contemporary device that produce visible lights, infrared or ultraviolet lights. LED does emit almost all colors by adding up the three color constituents red, green and blue lights.
The invention of LED revolutionized the history of lighting because it is brighter, cooler, more energy efficient and more durable when compared to conventional incandescent of CFL bulbs. Nowadays, LED lights are widely applied in residential, commercial, sports, filming and industrial areas. The different types of products include LED light bulbs, flood lights, color-changing RGB lights, spot lights, security lights, indicator lights and more.
If you are asking about LED in lighting, it has also two meanings – COB or SMD LED. They have slight difference on how do they work.
What does LED Stand For?
LED stands for Light Emitting Diode. When looking at the words individually, we can define each term as below.
| Terms | Definition |
| Light | The artificial illumination generated to make objects visible. It usually means visible lights |
| Emitting | Discharging the photons (or lights) |
| Diode | A circuit electronic that allows current flow in one direction, and suppresses it in the reverse direction. The diode is made of semiconductor, which provides medium for electron excitation. |
When a D.C. current pass through (usually 12V), bright light is emitted from the diode. By adding the LED lens having specific beam angles, we can make it becomes spotlights or floodlights.
What is the LED Symbol?
When representing the light emitting diode in circuit diagram, we need to use the LED symbol below.
The symbol of LED light consists of a triangle, a vertical line and two arrows. It is basically a diode symbol with 2 additional arrows. The arrows mean it is light emitting.
When we are drawing the LED circuit diagram, it should be noticed that the positive pole of battery connects to anode of LED lights. Otherwise, the bulbs will not turn on. In this setting, the current will pass from battery, then to LED, and then to resistor, lastly go back to battery.
How Does LED Work?
One of the fundamental knowledges about LED is the working principle, which means how does LED produce light.
The semiconductor is the essential components inside LED. When there is current flow through the circuit, the holes in P-type semiconductor and the electrons in N-type semiconductor will combine to together. This process causes the electrons fall from a relatively high energy level to lower, which in turn leads to emission of photons having the same amount of energy of this energy gap. In other words, the valence band (the holes) are basically creating the vacancy having low energy level for electrons to fall.
By using different P-type & N-type semiconductors, we can get photons with different visible wavelength and thus colors. Some of the common semiconductor includes the followings.
| Light Color | LED Semiconductor |
| Red or yellow | Aluminum Gallium Arsenide Phosphide |
| Green | Gallium Nitride |
| Blue | Zinc Selenide |
LED History
LED is one of the best inventions in human history because it solves many problems with incandescent, metal halide and CFL lighting. The incandescent has incredibly short life span, metal halide requires 5 to 10 minutes warm up time, while CFL contains toxic mercury. Nevertheless, LED improves all these problems, like it has 50x to 80x longer life span, LED reaches maximum brightness within a second, and it does not contain the volatile chemicals that contaminate our environment upon disposal. In addition, LED has 10x higher energy efficiency than incandescent. Energy crisis is always one of the historical issues in the world, the invention of LED significantly helps reduce the energy burden.
1. 1900s
A scientist working in Marconi Labs named Henry Joseph Round noticed that he can create a yellow light when he applied 10 volts to carborundum or silicon carbide crystals. However, no working theory was presented on why this was so until a Russian scientist named Oleg Losev published his paper in 1927 explaining the detection and oscillation effects that occurred using carborundum.
In 1955, Rubin Braunstein noticed that simple diodes gave off infrared light when connected to a current. A few years later, Gary Pittman and Bob Biard, both working at Texas Instruments, found that gallium arsenide diodes emit infrared light when connected to a current. This was the same year when they received the patent to infrared LED. However, their technology did not receive wide recognition because the light was not visible to human eyes.
2. 1960s and 1970s
The first working version of LED lighting first came out in the 60s when it was invented by GE scientist Nick Holonyak Jr. GE called the bulb ‘the magic one GaAsP or (Gallium Arsenide Phosphide). GaAsP was the first semiconductor to be used in the red LED bulbs.
A few years later, M. George Craford, a student of Holonyak’s invented the first yellow LED by using red and green gallium phosphide chips. During this time, he was also working on a brighter red LED. In 1976, Thomas P. Pearsall developed brighter diodes and a brighter red LED which was used in fiber optics and telecommunications. In Japan, Shuji Nakamura was developing the first blue LED which he perfected in 1979. This technology was later made available for commercial use in 1994.
Use for LEDs were often limited to industrial and laboratory uses because LEDs were expensive to produce. Fairchild Semiconductors worked on a new technique using a planar process to make the diodes cheaper and managed to reduce cost for individual LEDs to 5 cents, making LEDs widely available for commercial sale. Soon after, LEDs were being used in a variety of commercial and manufacturing purposes.
Further development led to the discovery of white light LEDS by coating blue chips with fluorescent phosphors. Development for white LEDs were supported by the US Department of Energy since white LED technology would prove to be cost-effective in lighting manufacturing, commercial, and other spaces.
Importance of LED Lights
The appearance of LED means it does a revolutionary change in lighting industry.
1. Top 3 disadvantages of incandescent bulbs
Before the popularity of LED bulbs, people relied heavily on incandescent. First, incandescent bulb is not energy efficient because it heats up the tungsten filament to generate light. Around 95% of energy is consumed to heat while only 5% turns to light. Second, the surface of incandescent is quite hot to touch. Your skin may get burnt if you accidentally touch the bulbs. The 3rd drawback of incandescent light bulb is that it goes off very fast (usually within 1000 to 2000 hours). The frequent replacement will lead to wastage of resources.
2. Why LED is better than incandescent and CFL
However, LEDs seem to solve all of the above issues. First, LED turns 95% energy to light by making use of semiconductor. So, we can see under the same power consumption, LED emits brighter lights. In other words, it means LED is more energy-saving because we can have smaller power LED to give the same lumen output of incandescent. For instance, a 10W LED bulb can produce nearly the same brightness of a 100W incandescent! In addition, the surface of LED bulb is relatively cool to touch, but there is still a little amount of heat if you have high power flood lights.
Although the lighting efficiency of CFL is in between incandescent and LED, CFL has another problem – mercury. The mercury is the essential component of fluorescent bulb as it provides medium for electron excitation and production of UV lights, then the phosphorus layer turns the UV lights to visible light. However, disposal of CFL bulb might lead to contamination of river, sea or farmland. Besides, if the phosphorus layer is peeled off, then large amount of UV light will come out from the bulb. It is hard to detect UV light by our eyes because it is not visible in natural. Nonetheless, this is not the case for LED bulb as we can control the wavelength of the lights emitted from LED, so we can eliminate the generation of harmful UV lights.
See also: LED vs CFL lighting
How to Choose the Best LED Lights
Some may also ask – what does the best LED lights stand for? It means it should be energy-saving, long-lasting, eco-friendly, durable and etc.
1. Energy & cost saving LED
One of the incentives of using LED light is the reduction of electricity bill. Since LED light has high luminous efficacy of 130lm/W (approx. 10x of incandescent), we can cut down the energy cost to 1/10 of the original value if we replace all incandescent and maintain the brightness in more-or-less the same level. When buying the LED bulbs, we can look at the “luminous efficacy”. Higher the value, more energy saving the bulb. The better LED would have around 100 to 130lm/W. If someone tell you their bulbs has over 160 or even 200lm/W, we should be extra careful because they are probably giving you the fake value.
See also: Do LEDs save energy?
2. Life span of bulb
If you want to save on the cost of buying lights in your home remodeling, commercial or industrial lighting projects, we can select the LED lights having higher life span. In general, the life span of LED flood lights or bulbs available in the market has the service life from 50,000 to 100,000 hours. The figure is incredibly high because we can do the conversion here. If we are using the LED lights for 8 hours per day, then the bulb can last for approx. 17 to 34 years. By switching to LED, we can also save a lot of replacement & installation cost.
3. No warm up time for LED
If you are using metal halide light in your backyard or football field, you will need to wait for about 5 to 10 minutes for the MH to reach maximum brightness. It would be quite inconvenient if you are having the backyard BBQ party with your friends, or going to play football with your team mates.
LED can be turned on and off instantly, which implies we have no need to wait for such a long period of time to have bright lighting. LED is especially useful for outdoor night activities because of its instant on/off ability.
See also: LED vs metal halide lighting
4. Versatile color temperature
In the lighting industry, we use color temperature to describe light color. In general, 2800K to 3500K means warm white color, while 6000K to 7500K represents cool white lights. If you want to create romantic and relaxing atmosphere in your living room or bedroom, then we can have warm white light. For football field, tennis court and other sports facilities, we will use natural white light or slightly cool white lights for better vision of athletes and spectators. The top LED light can even be bi-color, which means we can adjust the color temperature for different situations.
See also: Color temperature vs color rendering index
5. High CRI LED lights
CRI stands for color rendering index, which is an important parameter indicating the LED light quality. If the LED bulb has high CRI, it means we can see the more realistic color under this artificial illumination. Sun has the maximum CRI of 100. Broadly speaking, the LED having 80+ CRI is sufficient for general residential and commercial application. Some museums might require the lighting must have 90+ CRI, so the visitors can see the real colors of the paintings.
6. Versatile LED beam angle selection
To choose the best LED light, we also need to have a look at the beam angle, which stands for how wide the LED light will be spread. The typical beam angles include 30°, 45°, 60°, 90° & 120°. As we can see from the figure, the light intensity just fall outside the beam angle range is equal to 0.5 x maximum intensity. Small beam angle of LED means it is a spotlight, while large angle means flood lights.
In the photometric calculation, beam angle is a paramount parameter because it affects the ground lux level distribution (light uniformity). Depending on the size and shape of field, lighting engineer will make use of LED light having different lumen outputs and beam angles to achieve the best lighting uniformity. It is important because if the illumination is more uniform, we can see the objects clearly and pleasantly.
See also: What is lighting uniformity?
7. LED Luminaires that survive in extremely hot or cold temperatures
For industrial lighting, we will need LED lighting that works in extreme environment, which means burning hot or freezing cold areas. Due to the solid-state design, LED seldom has delicate components such as filament. By using the customized optics or adding the protective case, our LED luminaires can function normally from -40°C to 100°C.
See also:
a. Low temperature LED street lighting
b. High temperature high bay LED
8. LED Dimming & color-changing lighting control
Dimming is another great feature of LED lighting, some of the LEDs are dimmable, which means we can adjust the brightness to fit different applications. For instance, if we are having dinner in the backyard, we can dim the outdoor flood lights a little bit to have relaxing feeling. On the contrary we will need to have brighter lights for lawn mowing. Dimmable LED bulbs give a greater flexibility.
Besides, if we want to decorate our house in Halloween or Christmas, we can install RGB facade lights. Some of the LED has color-changing function. By adjusting the intensity of each color constituents red, green and blue, we can establish up to 16 million colors. With the use of wireless DMX controller, we can even manipulate the light color on smartphone or computer.
9. Compact and light-weight LED
The top LED light should be light-weight to guarantee safety. If the luminary is heavy, the cost of installation would be higher as we will need to do the reinforcement on your poles.
Before buying LED, it is better knowing the weight limitation of the mounting site, and then use this value to select the best lighting product.
10. Avoid blue light pollution
Blue light is one of the common problems of LED lights, as it can affect our sleep quality if our eyes are exposed to prolonged blue lights. The way to reduce the blue light content is to select the LED with lower color temperature (2800 to 3500K). For such the Kelvin value, the color of light is yellowish orange. It can also create cozy feeling at home & garden.
11. Price of LED lights
Despite the above LED advantages, its price is generally higher than incandescent, HID and other types of conventional lighting. Some may concern about the initial price of the lights. That is one of the factors we should consider; however, we also need to calculate the maintenance cost of the lights. If you are using halogen flood lights for your patio, you will need to replace this outdoor light every few months because of lumen depreciation. On the contrary, LED lasts for 10 to 30 years, so it can eventually save your lots of lamp cost and installation cost.
Applications of LED lights
As time goes by, LED has been widely adopted to different areas.
1. LED residential lighting
a. LED light bulbs
b. Recessed lights
c. Track lights
d. Outdoor flood lights
e. TV backlight
2. Commercial LED lighting
a. Downlights
b. Sports lighting
c. Parking lot lights
d. Airport lighting
e. Public park lights
3. Industrial Lighting
a. Factory
b. Warehouse
c. Foundry
d. Power station