10 Frequently Asked Questions (FAQ) on laser phosphor and RGB laser

Posted by (@Tom_Bert) in Professional cinema

DP4K-60L lightbeam
There's a lot of discussion in the market on laser light sources for cinema projectors. Two technologies are emerging and co-exist: 'laser phosphor' (or 'LP') and 'RGB laser'. To take away some of the uncertainties, we'll share the most Frequently Asked Questions (FAQ) on the topic (and their answers).

1. What is the technological difference between laser phosphor and RGB?

The light source in an RGB projector contains red, green and blue lasers. The light source in a laser phosphor projector contains only blue (and sometimes red) lasers, combined with a yellow phosphor wheel. Both types of light sources create a uniform white light interface that enters the engine; just like a Xenon lamp did before. Only when you analyze the spectral properties of this white light, you can discern the narrow bandwidth of RGB from the broader bandwidth of LP.

2. Why do the two technologies exist next to each other?

This is because the strengths and benefits of each technology serve different market segments. Where RGB technology today is an enabler for higher brightness and improved image quality; laser phosphor technology is a mainstream technology with clear TCO benefits.

3. Why did Barco introduce RGB projector models first?

When Barco started development on laser based projection in 2010, the first requirement from the market was to enable higher brightness than lamp-based projectors. This was linked to the ambition to project brighter 3D, as well as to serve the largest cinema screens with one projector. RGB is the technological enabler for these very high brightness projectors. 

4. Why did other brands introduce laser phosphor projector models first?

Other brands introduced low brightness (<<10,000 lumens) projectors based on laser phosphor technology as their first model. This was because laser phosphor as an enabling light source for projection could be leveraged from other markets; if brightness was limited to the one of those smaller-screen markets. The price point did prove difficult to bring a clear TCO advantage however. It is only recently with a second generation of laser phosphor light sources emerging, which also allow higher brightness levels, that the economic viability was proven.

5. Will both technologies continue to co-exist?

Very likely. Technological evolution and matureness will lead to brighter laser phosphor projectors as well as to economic viability of mid-sized RGB projectors; but 100% closing the gap will be difficult. Both technologies will keep their merit for the right market segment.

6. How do RGB and laser phosphor projectors differ in spec?

Looking across the portfolio of the RGB and laser phosphor projectors of different brands in cinema, the market is settling for some common trends. RGB-based projectors typically go up to around 60,000 lumens, with an estimated lifetime of 30,000 hours to 80%. The sweet spot of laser phosphor-based projectors lies around 15,000-25,000 lumens, with an estimated lifetime of 30,000 hours to 50%

7. Does laser phosphor always have a shorter lifetime than RGB?

No, this is a pure consequence of product design. When designing an RGB projector for high brightness, the importance of cooling is major. A well-designed cooling system also allows for a higher lifetime spec. When designing a laser phosphor-based projector for economic viability, the existing spec is where the sweet spot lies. RGB is not intrinsically longer-lived than laser phosphor: it’s all in the cooling.

8. Does RGB always enable higher brightness than laser phosphor?

No, this is a pure consequence of product design… up to a certain level. Because of the optical properties of a laser phosphor source, you cannot scale it to the same brightness levels as – the more collimated – RGB light sources. Apart from that, by adding more cooling, you could also build a very high brightness laser phosphor projector, but the economic model would not be beneficial (also not compared to RGB).

9. Does the same laser safety regulation apply to laser phosphor and RGB?

Yes, these regulations do not discern between laser phosphor and RGB. However, when doing the math and defining the metrics for a certain setup (hazard distance, separation height,…) they typically lead to – significantly – lower numbers for laser phosphor vs. RGB due to the typically lower brightness of the former. 

10. Can you see the difference of RGB vs LP on-screen?

Looking at the existing portfolio of Barco projectors: yes, because these have been designed to be different. The contrast and uniformity spec is higher on the RGB models. (Note that they are higher on laser phosphor projectors than they were before on the lamp models). The RGB projector was purpose-built for this: utilizing higher quality optics to increase sharpness and contrast. This is confirmed by many audience measurements. However, looking at what the technology can do, they both hold the same opportunity. The only thing that RGB can do, that is impossible with laser phosphor, is go to the theoretical single bandwidth gamut called Rec.2020

NOTE: This article describes laser cinema projectors. Looking for RGB Laser in 24/7 control rooms? Then read all about it here.

About the author

Tom Bert
Tom Bert is a senior member of the Product Management team in Barco’s Entertainment division; he is responsible for the digital cinema servers and projectors. Tom joined Barco in 2006 as Research Engineer for Barco’s Technology Center. In 2009, he joined the Product Management team in the Digital Cinema division. Since 2015, Tom has been actively working on digital cinema servers and projectors and he has been promoted to Sr. Product Manager. Based in Belgium, Tom has international experience in display technology. He holds a PhD degree in Engineering from Ghent University.

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