Visible sunlight has many different colors that come together to make white light. Each of these colors is possible by a unique wavelength of the photon is emitted.
When we talk about LEDs, while they do have various wavelengths and are polychromatic, as in, emit a range of wavelengths, they can still appear to output only a single color.
True single wavelengths are emitted by laser light diodes. And this is the fundamental difference that leads to a variety of other differences in how LEDs and lasers work and are used in various applications.
LEDs and lasers both emit photons to produce light. LED light is more dispersed and multi-directional, while laser light is highly focused, making them specialized in their function. Lasers are used in optics and electronics, while LEDs are the go-to for illumination.
How Does LED Diode Emit Light
The LED, or light-emitting diode, is a junction diode that controls the amount of electricity that flows through it. An LED is made from semiconducting compounds containing gallium and other materials to produce different colored light energy.
Blue and green LEDs are produced by Gallium, Indium, and Nitrate compounds. In contrast, red LEDs are produced by Gallium, Aluminium, and Phosphate compounds.
At the heart of the diode is a p-n junction, which contains holes. Through these holes, electrons jump across the junction, from p to n. In this process of recombination of holes and electrons, they change their state.
The extra energy released as electrons changes their state causes photons to be emitted.
These photons then interact with the other materials used in the LED and the current running through it to give off visible light!
This property is called electroluminescence. And that’s LED tech in simple words.
Another thing to note is that, once across the junction, the electrons at higher energy levels like to settle back into their original state. So, ‘reabsorption’ of electrons back into the junction can occur in the wrong direction.
This reabsorption leads to energy inefficiency, meaning less electrical energy is converted to light energy.
Despite that, LEDs have a high efficiency level converting about 90% of energy into light.
How Does Laser Diode Work
Lasers are a very cool phenomenon that is highly efficient in their design and engineering. The word laser stands for Light Amplification by Stimulated Emission of Radiation. Here too, current passes through gallium compounds at the p-n junction.
But in the case of lasers, stimulated emissions of photons to create a feedback loop, leading to all photons being in phase with each other, or coherent, and having the same wavelength, that is, monochromatic.
Essentially, a beam of photons is responsible for gradually filling up a chamber of a mirrored cylinder.
This mirrored surface reflects photons back into the atoms within the chamber, exciting their electrons. These electrons in an excited state want to release the extra energy, which again is in the form of a photon.
This newly-released photon adds to the photon beam inside the chamber, amplifying the reflection and excitation process.
Once enough photons are released, a light escaping cavity allows a narrow, bright, and focused laser light beam to be emitted. This laser beam is very efficient in its conversion from current to light, so it needs protective eye gear to work with.
This efficiency allows a laser to get significantly hot. The power output of a laser diode is between 1 to 500 mW, depending on the safety class. A Class 2 standard laser pointer outputs about 1 mW. While a high-powered Class 3B laser needs protective eye gear as it outputs 500 mW.
Due to this high-energy precision, lasers are used in commercial work, like cutting diamond or metals, or for delicate eye surgery in LASIK. They carry signals over long distances and so are used for telecommunication. They are found in laser printers, fibre optics,
LED And Laser Diode Characteristics
While both LEDs and Lasers use p-n junctions and current to emit photos and produce visible light output, they differ in some fundamental ways.
|Principle of Operation||Electroluminescence||Stimulated Emission|
|Electrical to Optical Efficiency||10-20%||Up to 70%|
|Wavelength Spectrum Width||Wider, 25 to 100 nm
(10 to 50 THz)
|Narrower, <10-5 to 5 nm
(<1 MHz to 2 MHz)
|Coherence||Coherent wavelengths in phase||Incoherent light dispersion|
|Chroma||Polychromatic, has multiple bands of wavelengths||Monochromatic, has a single color wavelength|
|Output power||Low power, output is proportional to the input current||High powered from, from 1 mW to 500 mW, proportional to current above the threshold|
Advantages And Disadvantages Of Laser Diodes And LEDs?
Since the working and application of both lasers and LEDs are quite different, so too are their pros and cons.
Let’s have a look at some of these advantages and disadvantages of both light technologies.
LEDs are much cheaper to both produce and maintain. That is why they are used in everyday commercial and household settings to provide light. LEDs start emitting light at only about 50 mA.
Lasers, on the other hand, are more expensive to maintain and operate. Lasers require a higher current to maintain the high energy state of electrons. The current needs to be above the 40 mA minimum threshold.
The high power output of lasers can erode the pinpoint equipment that emits the light beam, making their application highly specific, such as for fiber optics. For comparison, LEDs emit dispersed light, so if LED shines over 1 mm square, a laser can shine on just 10 microns square.
LEDs also have a longer lifespan between the two. But while lasers have a much higher power efficiency level, they are still far from used as a means of illumination. At least not for another few years.
Now you know the fundamental difference in light generation and emissions of LED and laser diodes. They are quite similar in design, but they differ significantly in an application with a few key changes.
Did you know that LEDs are close to laser technology?
Have you seen laser applications around you in a non-commercial setting?
Share your thoughts with me in the comments below.