Projecting an image on the screen needs a powerful stream of light, otherwise the image will be dim. For a long time, discharge lamps were the only light source which could provide sufficient brightness for a projector. But in recent years the lamps have serious “competitors” – alternative light sources, and every year there are more and more models based on them. Let’s talk about the kinds of lampless projectors and their applications.
So what did not please the discharge lamps that they had to look for a replacement? It’s all in the peculiarities of their work and the device.
The main drawback – a fairly short service life would. During operation the lamps dim gradually, and at some point their brightness fades so much that it is necessary to replace them. The average lifetime of a lamp in high brightness mode is 3000 hours from 1500 to 4500 hours, depending on different factors . A more forgiving “economy” mode and a number of features that save the lamp life can extend the service life up to 4000-8000 hours, but its power will be lower.
But sooner or later the lamp has to be replaced. And then there is the problem of buying and installing a new. Manufacturers try to make lamp replacement as simple and convenient as possible, but the cost of lamps is still very high. This problem caused such phenomenon as the selling of the second-hand projectors with the comment like “it is fully working, you just need to change the lamp”. This “only” says a lot, because the price of a lamp can be up to half of the cost of a new projector.
Therefore owners find it easier to sell the unit with expired lamp and buy a more modern one, than to spend money on consumables. Lamps are especially problematic when projectors are used all day long, so you have to replace the light sources every few months.
Before going to full power the lamp is heated up for some time, and after work it must be allowed to cool down otherwise the internal components of the machine could suffer from heating . Should the user press the off button by mistake during a showing, the projector can not be switched on again straight away, one has to wait until it cools down, and then warms up to start again. Many models, however, allow you to turn the power off immediately at the end of operation.
There are a lot of complaints about the lamps because of the mercury vapor they contain – they require special disposal.
Lamps have been known to explode during use. But we can’t say that this is a frequent occurrence.
All these reasons have urged projector manufacturers to look for a worthy alternative to lamps. The new light source had to work much longer than the lamp in the first place. It was also important that it retained its high power while being more environmentally friendly. As a result of these studies, lamp-less light sources based on different technologies LED, laser, laser-LED , with their own advantages and disadvantages, appeared on the market.
Projector in the palm of your hand
The first thing that caught the attention of engineers were LEDs, known for their durability and low power consumption.
LED light sources can last 20,000 hours or more, which is several times longer than the life of the lamp. However, this technology had its limitations – at high brightness of red and blue LEDs, the green ones were weak. Therefore in a “pure” form LED-technology has found application in models of rather peculiar segment – pocket projectors.
The emergence of devices of such a small size was expected against the background of the rapid development of the gadget market. After all, if instead of laptops tablets and smartphones are widely used, then why not be a projector to match them. LED-technology is a must, because you need the same mobile projector for work with mobile devices: autonomous and not tied to the outlet by the power cord. A powerful gas-discharge lamp from a compact battery will not work, but the LEDs can be satisfied with a small.
Modern models allow you to project for an hour or two on internal battery power only, and some models e.g. Optoma RK301+ and PR320 have a possibility to connect additional external batteries for a longer work time in addition to their own batteries. At the same time the weight of the projectors is extremely small, from a few tens to several hundreds of grams. Not so many companies make pocket sized projectors, among them are ZM, Aiptek, Optoma, Philips and some more brands.
Their autonomy and small size impose their own restrictions on the brightness of such devices. When it comes to the luminous flux of pocket-sized models we are not talking about thousands or even hundreds of ANSI-Lm, but literally dozens. Accordingly, they can’t make a big image with a strong external illumination. But when it is darkened or the projection is small they can make a rather clear and bright picture.
The “pocket” format also determines other characteristics of the projectors: they are quite different from their stationary counterparts. Their functionality is affected by various factors. For example, while most ultra-portable tube models now have a resolution of at least XGA 1024×768 pixels , microprojectors tend to have less than. Also, lamp projectors’ optics is usually equipped with a zoom if it is not a short-focus model, of course , and pocket-sized apparatuses don’t have a zoom most often.
The communication capabilities of this class of projectors also have their own particularities.
Some models are designed specifically to work with certain types of technology – for example, tablets and smartphones based on Android or iOS Aiptek has such micro-projectors in its line . Such devices are equipped with special connectors for connecting to mobile devices. Often the connection to the signal source itself is based on a docking station, and the body of the device may have a special shape with a niche for a smartphone Other models connect tablets and smartphones via adapters.
Many projectors are equipped with USB cable inputs for flash drives and other devices cameras, computers , as well as some standard inputs for video sources HDMI, VGA, composite RCA, etc .d. . Models that support demonstration from memory cards for which separate slots are provided on the case are widespread. For recognition of files of different formats pocket projectors are often equipped with media players.
Scheme of hybrid laser-LED light source using Casio Green Slim projector as an example. In this model, the blue and green colors creates the blue laser bombarding the phosphor, and the red color provides a red LED
Not all microprojectors need external signal sources for projecting content. Many models are equipped with built-in memory sometimes quite extensive – up to several gigabytes , where you can pre-record the necessary files. Pocket-sized projectors also usually have built-in speakers so you can play sound without any speakers. Like conventional lamp machines, micro projectors can be built based on different projection technologies. The most widespread models are those based on DLP and LCoS technologies.
Low weight and long projector lifetime are useful features for situations when you need to carry the projector around. Therefore, LED-technology has also found a use in ultra-portable projectors for outdoor events. Such models, even though they are based on the LED light source, differ from their pocket-sized “brothers” in their features. Above all they are brighter devices – their luminous flux usually averages 100-500 ANSI-Lm, although some projectors have power up to 1000 ANSI-Lm.
Such models, on the one hand, are powerful enough to project a bright picture on the screen without much darkening of the room, on the other hand, they keep light weight. Ultra-portable LED projectors weigh about 0.3-1 kg, they are compact and can be easily placed in the bag. Produce such models and large manufacturers, known for the most part, lamp devices, and companies offering a variety of peripherals for computers, smartphones and tablets. Among the brands of LED projectors are, for example, ZM, Acer, Aiptek, BenQ, LG, Optoma, Philips, Vivitek
But the higher power has its own price – the loss of autonomy. Most models in this class require a network connection to work. However, there are exceptions. Built-in batteries can be found in some low-power devices Aiptek PocketCinema V100, Philips PicoPix, etc. . .
To some other projectors it is possible to connect specially designed for them batteries which allow to project without a network supply. Vivitek Qumi Q2 and Q5 and BenQ GP3 for example have this option. However, when powered by a battery the luminous flux of such projectors is reduced and becomes on average about 50-60 ANSI-Lm, t.e. Many times less than when connected to the network.
In turn, larger than in handheld models, size allows you to fully equip the ultra-portable projectors with connectors for connecting the most common signal sources. You can find HDMI, VGA, composite RCA and other inputs in these devices. Like microprojectors these models are often equipped with USB ports to receive video and audio signals from external sources via USB Display technology, to connect a “flash drive” with recorded files or even an optional Wi-Fi adapter, SD-card slots in these models are also not uncommon.
Such projectors are equipped with media-players for viewing popular file formats of movies, music, images, presentations and documents. Some have built-in memory for recording files. The ability to project content without using a computer or video sources is very convenient: you don’t need to carry heavy equipment, you can just take a projector, a memory card or “flash drive”, or copy all the necessary data to the projector memory, and nothing is superfluous.
Resolution of ultra-portable LED projectors is also higher than that of pocket LED projectors, most often WVGA 854×480 pixels or WXGA 1280×800 pixels , although there are devices with other types of resolutions. The tendency towards the “wide” format is due to the fact that these models are actively used not only for presentations but also for watching movies. The units are usually equipped with speakers and often tripod mounts just like cameras. Their optics are usually fixed, although there are some examples with an optical zoom
Despite the fact that LED models have no “rivals” from the side of lamp projectors in the segment of pocket projectors, the main areas of projection equipment – education, office presentations, conference halls, Digital Signage, etc., do not have LED models.d.- Low-power LED-based devices could not seriously compete with the lamp ones. To work in a well-lit room with a big screen the projector needs at least 1500-2000 ANSI-Lm so that people can both see a clear picture and take notes. LED projectors have barely reached the power of 1000 ANSI-Lm. To make the new lamp-less units competitive it was necessary to solve the problem of low brightness of green LEDs – to find a decent replacement for them.
And the solution was found! Instead of green LEDs manufacturers began to use phosphor bombarded by a laser, and in some cases the laser has replaced the blue LEDs. The resulting light source was no longer a “pure” LED technology, but a laser-LED hybrid. The luminous flux power of the models went up – went beyond 2000 ANSI-Lm, previously unavailable for LED-devices, and by the current moment reached 4000.
For the first time hybrid light sources were used by Casio, which abandoned completely the lamp projectors and focused its efforts on developing laser-LED devices. Later on, when the “hybrids” were well established, devices based on laser-LED technology began to appear in the product lines of other major manufacturers. For example, there are such models in Acer, Optoma, Panasonic, Viewsonic lines, the “hybrid” models from Mitsubishi are planned to be released.
What advantages do the “hybrid” models have in comparison with their lamp counterparts with the same output of light current?? First of all, the source has many times longer lifetime than the lamps – up to 20,000 hours. Secondly, low power consumption and no mercury. Thirdly, the projectors can be switched on and off quickly without warm-up and cooling down.
The special thing about the laser-LED models is their relatively high price as compared to their lamp counterparts. But it is worth taking into consideration that in conditions of intensive use of the device its price will be paid off quickly due to the low maintenance costs. Because replacement lamps for projectors are expensive, and the hybrid models have no lamps, you do not need to change the source. So in the long term “hybrids” are even more economical devices and that’s not even taking into account their low power consumption .
What does the hybrid projector market offer? The models are diverse not only in their features but also in their purpose. There are the light variants for mobile presentations, the state-of-the-art devices, and even the short-throw ones. Each unit is niche-oriented.
The widest line of laser-LED models is released by Casio. It offers two series of medium-focus ultra-portable and portable projectors – the slim, lightweight Green Slim and the more massive Standard, both with a light output of up to 3000 ANSI-Lm. The company also produces powerful stationary projectors Pro up to 4000 ANSI-Lm and Short Throw up to 3000 ANSI-Lm . The last two lines support interactive functions.
“Hybrid” models by Optoma are represented by short-focus XGA and WXGA units with luminous flux of up to 2500 ANSI-Lm.
Acer has a universal projector K750 with the power of 1500 ANSI-Lm and Full HD resolution, which can be used for presentations and for watching movies without image compression. However, this is not the only “hybrid” Full HD unit on the market. ViewSonic company releases a model of Pro9000 1600 ANSI-Lm with 1920×1080 resolution designed for home theater.
Panasonic also produces Full HD projectors on the basis of laser-LED light sources Solid Shine series models . Unlike other models with the same solution these devices are heavy and powerful stationary devices for large rooms, with light output up to 3500 ANSI-Lm, function of lens shift and support for data transfer via HDBaseT technology.
Almost all existing models on the market based on hybrid laser-LED light sources are DLP projectors. This technology has a number of advantages, one of which is a possibility to easily display 3D images. Not surprisingly, many “hybrids” are capable of playing back three-dimensional pictures although usually not with glasses .
Laser light sources are another promising alternative to discharge lamps
BenQ LW61ST+ Short Throw Laser Projector with BlueCore Technology
has been on the market for a long time, but there are not many projectors based on them yet. The main advantages of laser light sources are similar to the “hybrid” laser-LED ones – their lifespan is also about 20000 hours, they can be switched on and off quickly too, they do not contain mercury. And power of luminous flux of such models is high – at the moment up to 4000 ANSI-Lm. In addition, laser projectors are characterized by quiet operation.
The peculiarity of laser technology is that it allows to create a light source without using light emitting diodes. This can be accomplished in a variety of ways. For example, it is possible to achieve primary colors using red, blue and green lasers, but such technology is expensive. Another option is to use a laser of one color as a rule, blue bombarding a color wheel with segments of a special luminous composition. BenQ L-series laser DLP projectors are made exactly according to this technology BlueCore . These are short-throw units and their luminous flux reaches 2500 ANSI-Lm.
Sony company, which this year released its first laser projector VPL-FHZ55, used another technology. Here the laser affects a wheel with a special light coating to get a stream of white light, and then using dichroic mirrors to split it into three – red, blue and green. Then these streams pass through three LCD panels and through dichroic prism are gathered together forming a single picture. The VPL-FHZ55 not only excels with projection technology and it is the first 3LCD laser projector on the market , but also with characteristics that make it stand out from other lamp-less projectors. This is a powerful installation unit with a light output of 4000 ANSI-Lm and WUXGA resolution with lens shift function and interchangeable lenses.
Powerful as can be?
Laser-LED and laser projectors can seriously compete with lamp models in certain market segments. On the level of power they are already equal to the majority of portable, short-throw and stationary projectors. But at the moment even the brightest existing incandescent devices reach luminous current of 4000 ANSI-Lm, while among lamp devices there are more powerful models – both single-lamp models and double-lamp ones.
Nevertheless, it is already possible to receive luminous flux higher than 4000 ANSI-Lm with the help of lamp-less projectors. But not with one projector, but with two or more. The way of adding the light flux of several devices is well known for a long time – the stacking method two devices in a stack , successfully applied to the lamp models, is also suitable for projectors with alternative light sources.
It can be easily realized if the set supports lens shift function and there are already some models of this kind on the market e.g. Panasonic Solid Shine, Sony VPL-FHZ55 . Another affordable option is the XJ-SK600 stackable system with two pre-installed laser-LED projectors which allow images to be aligned together, even without lens shift, thanks to digital correction.
Projection without lamp: an overview of lamp-less projectors