Laser – an acronym for Light Amplification by Stimulated Emission of Radiation. But what does it mean in the context of AV? And what does the future hold for laser as a projection lightsource? AV News examines the current status of laser technologies and assesses the prospects for a future that will see pure laser lightsources migrate – even to the consumer market.
What does laser projection mean to you? The hybrid LED / Laser solid state models brought to market by Casio and ViewSonic? The laser phosphor technology at the heart of projectors developed by BenQ and Sony? Or the pure laser diode technology recently introduced by NEC Display Solutions? Martin Large, CEO of Steljes, acknowledges that: “As there is no industry accepted definition of what laser projection actually is, it covers a multiple of different types of projector.”
“Manufacturers and users alike have been looking to alternatives to the traditional metal halide lamp used in data projectors since the technology was first introduced,” continues Large. “Metal halide lamps offer a pure white light, but require high voltages, contain poisonous mercury, are relatively inefficient, leading to high temperatures and increased running costs – and are relatively short-lived, requiring periodic replacement.”
“With developments in LED and Laser technologies, it is now possible to use both Laser and hybrid LED / Laser technologies which offer an appropriate brightness for general usage at a reasonable price point. Since their introduction, Laser and hybrid LED / Laser technologies have become increasingly popular with customers – offering increased efficiency, excellent projection quality and a significantly longer lamp life – to the point that the lamp generally will never be replaced during the operational life of the projector.
Technologies
Typically, a hybrid Laser projector might use three different light sources – red Laser, blue LED and green from the phosphate colour wheel. A Laser phosphor device, such as BenQ’s LTW61ST, uses a blue Laser diode with an 8-segment phosphor colour wheel. The BenQ LW61ST is the first in the world to be equipped BlueCore, a light engine that takes only takes a few seconds to reach full brightness and to cool down.
Traditionally, choosing the right Laser / LED projector tended to be more of a budgetary rather than a functionality issue. “However” says Large, “we are now finding that customers are increasingly looking beyond the headline price and looking at total cost of ownership by calculating the costs of maintenance and lamp replacement. This is driving the adoption of pure Laser source projectors. BenQ’s range of Smart-Eco projectors offers savings over the life of the projector. It has been estimated by Futuresource that schools, for instance, could be saving £298 in energy savings and 159kg in CO2 (based on average projector usage of 6 hours per day) over three years.”
As the first to market with a projector designed around a Laser light engine and a phosphor colour wheel, BenQ claims an advantage in colour stability over the life of the unit. BenQ’s SmartEco laser source projectors have a minimum expected lifetime of 10,000 hours so there is no need to replace the lamp. The projector is claimed to save up to 90% in electricity consumption when compared with conventional projectors. An Eco Black Mode automatically activates after 3 minutes when not connected to a display source – helping to reduce unnecessary power consumption.
Laser phosphor
In addition to the well document Laser / LED Casio range, ViewSonic has adopted a similar form of hybrid technology. The company points to both the environmental benefits and the high contrast ratios of more than 10,000:1, supporting home cinema applications and other colour critical applications. ViewSonic’s Solid State Illumination (SSI) architecture is described in a company white paper as using a blue Laser light filtered through phosphor to produce the colour green with LEDs providing the red and blue colours.
Built using 405nm solid-state Laser diodes (similar to Blu-Ray) the Laser engine generates modulated beams that address the pixels of the phosphor panel. Mirrors are used to direct the beams over the entire display area. With a scan rate of up to 360Hz, flicker-free video can be displayed with no motion blur. The modulated beams from the Laser engine are used to excite the phosphors and determine the brightness of each pixel. The phosphors are printed extremely close to the panel’s surface, achieving a 178° viewing angle.
Laser / LED Hybrid projectors generally output about 100 lumens per laser. In terms of energy efficiency, Laser / LED hybrid models produce nearly twice as many lumens per watt as a lamp-based projector. Some hybrid projectors also utilise intelligent power control. The projector intelligently controls the amount of power delivered to the illumination source in synch with the brightness required, saving further energy.
Pure laser
Laser / LED hybrid projectors have fewer lasers than a pure Laser projector. A pure laser projector typically includes 20 to 30 Laser diodes for a brightness of 2000 to 3000 lumens, and proportionately more for greater light outputs. The larger number of Laser diodes increases the cost substantially. As a new lightsource there almost no economies of scale to be enjoyed by projector manufacturer, and BenQ says that manufacturing costs are still significantly higher for a projector using a Laser lightsource than those for an equivalent lamp-based model.
Applications for pure laser are, then, restricted to the high-end at present (although the modest output from the Microvision pico projector is driven by a pure Laser lightsource). Gerd Kaiser is the product line manager responsible for NEC Display Solutions’ new pure Laser 4K D-cinema projector, shown at the company’s Solution Showcase. He explains that the new projector is designed around a lightsource comprising clusters of Laser diodes, emitting spatial coherent light of a very narrow spectrum, i.e. emitting only a single colour of light.
Planar Wave Guide Laser technology produces efficient light output which combines to create a larger colourspace than that available from conventional lamp technology. The Laser diodes create pure colours that are significantly different from traditional lamp-generated colours. Kaiser says: “Anybody who saw Xenon light before has the impression of excellent colours, but Laser colours are absolutely amazing, even compared to Xenon.”
He explains: “A Laser lightsource can be much brighter because of its high luminous efficiency, which means much more brightness compared to a similar projector design and similar thermal emission. It delivers an amazing colourspace which is much wider than lamp colourspace.”
“Brightness decrease over time is much lower than decrease of lamp brightness, which also has a big influence on service cost. The scalable Laser lightsource is separated from the projector and connected via a long fibre tube. Consequently, the projector head can be very small and installation is very flexible. Even free tilt is possible and the projector head is silent without the noise generated by lamp cooling. The TCO is much lower because of no lamp cost and lower energy cost.”
Pure advantage
While Kaiser concedes that the cost of pure Laser lightsources is currently very high NEC believes it will come down in the near future as numbers increase. Kaiser believes that this is essential for high-end models because hybrid lightsources are currently limited to about 6,000 / 7,000 lumens. Pure Laser lightsources have the potential for much greatness brightness, with about 70,000 lumens currently possible. Even at such extreme levels, Kaiser argues that the colour reproduction of Laser lightsource is much better, with pure colours and a much larger colourspace.
Current product safety regulation doesn’t allow higher Laser class than class 3R, equivalent to about 5,000 lumen brightness. But there will be a regulatory change in the near future that will allow higher laser classes to be used as projector light source. In fact, the light emitted from laser-illuminated projectors is processed in such a way that it doesn’t even legally qualify as ‘laser light’ when it leaves the projector. It is recognised within international safety-standards authorities that regulations need to be revised. As soon as regulations change, high brighter laser projectors will be offered.
Kaiser believes that the potential for pure Laser is outstanding: “As soon as the price comes down it will be the perfect lightsource for the future. The Laser lightsource is very bright, delivers unbelievably pure colour, operates in an excellent colourspace, is very efficient and last but not least, is very environmentally friendly. The brightness, colourspace and the colour consistency of Laser won’t deteriorate over time – the major advantage of laser light source.”
“Reliability is excellent. The expected lifetime is more than 20,000 hours. Laser diodes are arranged in clusters, so it isn’t visible if a single diode is not working correctly. Laser is also very efficient, nearly all energy is used for visible light (in the case of Xenon, only 35% of energy is used for visible light) and so brightness is much higher at same energy level. This enables design of much brighter projectors for premium applications such as 3D cinema on really large screens.”
