4K, HDR, LASER, LED. The latest developments in projection systems

Text: Javier Guerra


 

There is no need to go to great lengths to see that we have definitely reached a turning point, both regarding the technology for the reproduction of images and the content itself that we are going to broadcast through any modern visualisation system.

 

Within this qualitative leap forward, there is a segment of our market that has not been updated at the same speed and seems to have been anchored in the moments immediately before the beginning of the economic crisis that has been with us for a decade now. I am talking about Imaging Devices for professional use, which experienced their splendour in the years of economic prosperity. At that time, every month a Museum or Nature Interpretation Centre was opened, a Congress was inaugurated or an Exhibition or Trade Fair was created, the projection market reached its glory, making the greatest exponent of the technology of the time available to end users. Many of those projectors are still working today, but it is obvious that -immersed as we are in the world of Ultra High Definition- it is time to review the current state of projection technologies and their implementation in current devices.

 

Projection Technologies and Lighting Systems

The professional video projection sector is so broad, ranging from tiny devices for training in small classrooms to monstrous RGB laser film projectors that achieve brightness values of up to 60,000 lumens. However, their essence comes from the same three types of technology that has been around for years. That is, transmissive LCD panels, reflective LCD-based LCoS systems (mainly SXRD and D-ILA) and DLP technology projectors – both in single panel variants, as well as in Tri-DMD models. It is true that, little by little, traditional LCD technology has gradually reduced its formerly substantial market share in favour of DLP technology. Today, Texas Instruments panel-based projectors have massively taken over the most economical segment of the market, but it is no less true that thanks to LED lighting or laser diodes, any of the three technologies currently on the market are now capable of displaying images of the highest quality, even on large format screens.

 

Lighting systems used in imaging have traditionally been based on the use of UHP mercury vapour lamps or Xenon lamps. The advantage of the increased colour accuracy and colour stability of Xenon lamps was that they competed against the best electrical performance and longer life of mercury vapour lamps. Precisely for this reason, the markets for both lighting systems were well differentiated, with Xenon-based systems prevailing in applications with higher requirements for faithful colour reproduction and UHP in installations where low maintenance costs were paramount.

 

Since the middle of the last decade, the first projectors with lighting systems based on RGB LED light emitting diodes began to appear. Several projector manufacturers incorporated different variants of these LED systems, which were mainly characterised by very low brightness, making them unsuitable for professional applications where ambient light cannot be fully controlled. A couple of years ago, one of the most important companies in the lighting segment -the Dutch company Philips- presented a variant of this lighting system called HLD LED, which, thanks to a drastic improvement in the density of its diodes, solved this problem, achieving brightness values in the region of 3000-4000 lumens. This enabled these devices to be classified as appropriate light sources for educational applications and professional environments. At ISE 2017, the company added the Home Cinema projector variant to its portfolio, which, with values between 1000 and 2000 lumens, already curried favour with at least two of the largest manufacturers of DLP projectors on the market, such as Taiwanese Benq and Optoma. There are also two main advantages over traditional lamps. The first and foremost is that its service life reaches 20,000 hours of use, which, in terms of savings in maintenance costs for projectors operating 24/7, can result in a very considerable figure. On the other hand, the light emitted by these devices allows manufacturers of DLP chip-based projectors to achieve a colour reproduction that is much more faithful to the original. In fact, we can go from only just covering the Rec.709 colour space of HDTV broadcasts when we use traditional lamps, to reproducing up to 100% of the DCI-P3 colour space that is the norm in Digital Cinema and UHD content, which translates into a 26% improvement in its ability to show colours that the human eye can see.

 

Projection Systems
HLD-LED lighting system operating scheme

 

With decades of experience in the use of laser light diodes for the most diverse applications, it was only a matter of time before these lighting systems entered the imaging segment. It is obvious that the theoretical ideal for a projector with this type of lighting, should have at least one laser emitter for each of the primary colours -Red, Green and Blue- that compose the image and even better, two for each colour -one for each eye- in 3D projection systems. Regrettably, the price to pay for these devices is stratospheric and only the most modern and luxurious cinemas in the world have systems like these. For all other laser projection devices, we have to use systems with a single emitter bank, or hybrid systems. The most common and the one we can find in some single panel devices dedicated to Home Cinema involves generating a blue beam of light by means of a bank of laser diodes of this colour, which is led through a focus lens towards a phosphorous wheel in which it decomposes at different wavelengths, thus obtaining the yellow and green colours. The sum of BGY is passed through a second wheel, -this time a colour wheel that can vary between 4 and 6 segments depending on whether you are looking for more brightness or greater chromatic fidelity- and this way, we can obtain the 3 primary colours that will make up our image. If we want to obtain a significant increase in the brightness of the projector or its contrast ratio, the toll to be paid unfortunately involves a loss of performance in the red colour. This is the reason for the recent appearance of the most advanced hybrid systems, which can include a second red light emitter in the form of a LED diode or even a second bank of red laser diodes that dramatically increases the accuracy of colour obtained. The inherent advantages of using solid-state lighting sources over traditional lamps are concentrated in any of these technologies based on the use of laser diodes. Brightness in the order of several thousand lumens, the reproduction of colour spaces as wide as those required in cinematographic applications and the duration of more than 20,000 hours of use with negligible losses in its luminous efficacy.

 

Projection_Systems_3

 

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