The difference between LED and laser projectors

Lamps, LEDs and Lasers are the three most common light sources for projectors, with the latter two quickly gaining market share. Lamp based projectors are still commonly used today in home theaters, that generally operate only a few hours a week. However, their limited lifetime is not very appealing to professional customers. Especially when used intensely, LED and laser replace lamps as both the most desired and most economic option. In this article, we therefore only focus on LED and laser.

Over the past few months, we have been talking a lot about the advantages of laser projection vs. LED – its higher brightness, longer lifetime, lower power consumption, and lower total cost of ownership (TCO). We have shown the graphs and statistics to prove all these benefits.

But today, I want to tell you WHY laser illumination is so much more awesome than LED. Now don’t expect me to dive into quantum mechanics, because the details are complicated and not really my domain. But I can tell you the basic principles, which is all you need to know to understand any conversation on the subject. It’s a bit like learning history by watching cartoons: you won’t become a professor, but you will understand the essential themes and concepts.

The perfect coherence of laser light

One of the biggest differences between laser illumination and LED is the brightness produced by the projection system. For the same power input, laser light engines beat LED engines any day. The reason is focus and teamwork. A laser produces a really focused light beam. If you point it at something, it produces a dot. For LED lights, this is very different: the light is much more scattered and creates a large circle.

Let’s draw a comparison: take a horde of medieval soldiers that want to break down a castle’s door using a battering ram. If they all run together, at the same speed and in the same direction, they will develop a tremendous force. If on the other hand, they run at a different speed, in random directions, they will create a much smaller force and not even dent the castle door. Although the undisciplined horde uses the same amount of energy for their attempt, the force on the door will be much lower.

The same concept applies to light. Laser light is by definition coherent. This means that all light photons are in exact pace and moving in exactly the same direction. LED light (and all natural light by the way) is not coherent, so the photons do not all move in the same direction. The energy of the beam is therefore much less focused, and more energy is lost.

Creating exactly the right color

Another reason is that the bandwidth of laser light (this is what defines the color) is very precise. If you draw a diagram, it will almost be a straight line. This means that the generated color is completely accurate. For LED light, this is a ‘bell’ shape, meaning there is a much wider distribution of colors but less saturation. Furthermore, this explains the color accuracy of laser sources. Because we know exactly the wavelengths of the three primary colors (red, green and blue) of the projector, we have total control over the colors produced.

New evolutions

Laser light sources have at the moment the advantage of high brightness. If this will remain the case is however somewhat questionable. Significant investments have been made in LED light sources, and the newer generations are catching up with lasers.

They probably will never reach the very high levels needed for example for projection mapping on buildings, but for other applications LED projectors definitely have a future beyond home entertainment.

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