- In practice
|TCO xenon lamps|
When considering an investment, one should not only look at the initial purchasing costs, but also at the operating costs, sometimes referred to as Total Cost of Ownership (TCO), which can have a considerable impact on the total costs of the investment. One of the factors that can influence these costs is the type of xenon lamp that is used.
Different lamp types
In cinema, basically three different xenon lamp types are used: the standard xenon lamp, the high efficiency lamp and the digital cinema lamp. All of these lamps are so called short arc lamps: the distance between anode and cathode is short, as opposed to long arc lamps which are not used in cinema. Because the arc gap (equal to the light emitting area) of short arc lamps is very small, they are suitable to be used in optical systems found in 35mm and digital projectors.
With equal power consumption, high efficiency lamps are brighter than regular lamps; they produce at least 10% more light. These lamps can be useful in situations where there is not enough light on the screen, but a more powerful lamp is not possible. High efficiency lamps are about 10% more expensive than standard xenon lamps and under normal conditions have the same life span. They can also be used at lower power, called 'Eco Mode' by some manufacturers, giving the same amount of light as regular lamps, but saving on energy costs. Manufacturer Ushio prolongs warranty life with 50% when these lamps are used in this way.
Digital cinema xenon lamps are specially designed to be used in digital cinema projectors. They generally have an even shorter arc than regular xenon lamps, producing an intensified spot of light. This helps to focus the light on the chipset, giving a better light efficiency. Some digital cinema lamps are specially designed and optimised for a certain projector model. In digital cinema, the mirror (also called reflector) is often specially designed to get the highest light efficiency. The lamp should therefore closely match the specifications of the mirror, in order for it to give the optimum result. Digital cinema xenon lamps normally last as long as regular xenon lamps, but special lamps for extra high output (for 3D etc) have a life span that is significantly shorter (about 50%).
Naturally any exhibitor wants to use a lamp that is cheap to acquire, with high brightness, low power consumption and a long life span. However, exhibitors are generally not aware that there is a choice, although a limited one, of xenon lamps. Being aware of this choice before making the initial investment, could lower the Total Cost of Ownership. This is where the projector that one wants to buy comes into play, as some projectors have a higher light efficiency than others. Some manufacturers have addressed this issue, stating the 'Lumens per watt' of their systems.
With Series 1 DLP Cinema projectors, the digital projector would generally require a much more powerful xenon lamp for the same screen as the 35mm projector. With the new Series 2 DLP Cinema projectors, all projector manufacturers have managed to raise the light efficiency, diminishing differences between manufacturers, but not eliminating them. For the Series 2 one can generally use lamps of similar wattage as the 35mm projector, the only difference being that the digital projector uses a high pressure lamp. Understandably running costs have lowered considerably with the arrival of the new projectors.
But is there really a choice in which lamp to use? Some manufacturers recommend using a certain type of lamp, sometimes even branded as their own, as it is said to make an ideal match with the projector. This is especially the case when the design of the projector mirror (also called reflector) makes a match with this particular lamp, as its electrode shapes follow the reflector geometry. Therefore the electrodes don't cast a shadow on the mirror and no light is wasted by spilling over the edge of the mirror. But most digital projectors are said to work with several types of lamps, and projector and lamp manufacturers can provide exact lists of possible combinations. However, these lists are not very long and some d-cinema projectors are not compatible with all xenon lamp brands.
So which type of lamp should be used when there is a choice? Due to their relatively low light output, for Series 1 projectors it seems advisable to use lamps with very high efficiency. This could be particularly true for projectors that cannot be fitted with more powerful lamps like the smaller projector models, or for projectors in auditoriums with very large screens.
Projectors often come fitted with a lamp designed specifically for this certain type of projector. These lamps are often considered to be the best choice for a projector and are offered by the projector manufacturer as the original part. Other companies might also offer similar lamps as a replacement for the original part. It is up to the projector manufacturer which brand of lamps he allows to be installed in the projector.
In some projectors it is possible to use standard 35mm xenon lamps as a cheaper alternative, even though not everyone is aware of that. These lamps are not only cheaper to buy, but also have a longer life expectancy, resulting in a low TCO. Not all projector models can be fitted with these lamps and special brackets or adapters may be required. If maximum light output is not required these standard lamps can be a good alternative, but only if maximum current and life span are respected. It should however be noted that if a more powerful lamp is required due to light efficiency, the net gain is reduced by the higher electricity costs.
A lot of the new generation projectors can only handle specially designed lamps and do no longer have the option to use 'standard' lamps; in most cases the design of a standard xenon lamp will not fit into recent digital projectors. Those 'special' lamps do not only have a special construction (size) or higher output, but also the capability to handle higher currents - or even over current - compared to their 'standard' family members. Some manufacturers divide these lamps into high power and long life versions (NEC) or have special lamps for high output (3D) like Christie (the SD series). Lamps that generate extra output wear out faster and have limited operating hours.
It is sometimes possible to fit a lamp designed for one projector into another projector. For instance an Ushio DXL60BA2 designed for a Barco can be fitted into a Christie projector if the anode cable is removed. And an Ushio DXL40BAF, also designed for Barco, can be fitted in a NEC projector if a special adapter is used. In cases like these, one should check if this construction is still covered by warranty.
In series 2 projectors the lamp uses less power in 2D than with 35mm film, so 2D digital screenings are cheaper to run than 35mm screenings. It should however be noted that xenon lamps for digital cinema cannot be used as much over their official life span as is possible with 35mm lamps. They really have to be replaced soon after they expire, when the fall off rate is very high.
The series 2 projector created a new issue on very small screens: too much light. Even when using a small lamp (often the smallest lamp possible) there is sometimes still so much light on the screen that 2D is above 30 ft/l and even 3D is well above 6 ft/l. This is much higher than any DCI spec and also gives problems in 3D, since the filters cannot handle this much light causing strange ghosting effects to appear. The only option here is to use a so called Cat eye (diaphragm) in the optical system, lowering the light throughput, which is understandably not very good for light efficiency.
2D / 3D
With the multitude of 3D films on the market nowadays, 3D is a major point of consideration when considering which xenon lamp to use. Because of this light inefficiency, 3D requires a strong lamp for optimal light output. Therefore it is worth looking at the use of the digital cinema projector: is it mainly used for 3D or for 2D?
The choice in 3D systems is a major issue in lamp requirements and can be a very important point when calculating total costs. The systems that can be used on a white screen (like Dolby and XpanD) require the most light (also depending on the gain of the white screen). Polarization systems like MasterImage and RealD use a silver screen that has a better reflection. The RealD XL system can be considered the most efficient and requires the lowest lamp power (or can handle the biggest screen) and the Sony 3D system ( RealD XLS system) is also very light efficient.
Almost all digital cinema projectors can nowadays set lamp power to match different formats. Light output increases with 3D and decreases with 2D; the lamp is strong enough to ensure a good 3D projection. The light intensity is then automatically reduced when the projector changes from 3D to 2D screenings. This feature reduces the light output and prolongues the life of the lamp. Issues that used to be associated with this in the past, like older xenon lamps that were difficult to start have been eliminated.
If a projector is used for 3D most of the time, the hours that it plays 2D (with the same large lamp) do not matter that much to its degradation. With the elimination of the projectionist in larger cinemas in the future, some 3D systems (like RealD XL) will stay in position even when screening 2D films. In this case the extra light is also needed for 2D screenings. This is not the proper way to use the equipment and does not give optimum quality in 2D, but is unfortunately very well imaginable.
Barco has been using a modular projector design since the first DP100 digital cinema projector. The modular design facilitates swapping parts and it is therefore easy to change the complete lamp house of a projector, which contains the xenon lamp. Barco recommends using different types of lamps for projections in 2D and a more powerful one for 3D. The projectionist pre-installs the different lamps in two of these lamp houses and since these are very simple to install in the projector, he can alternate the two types of lamp houses easily, without losing time or money. This is also made possible because the projector recognizes the lamp house and readjusts to the correct settings.
However, not many exhibitors are aware of this possibility, so not many cinemas use this option. Also: it's not quite as simple as it's made out to be – the swap should be done with care and one should wait at least 15 minutes for the lamp to cool down and also track exactly which screenings are 3D or not, which is not always easy in multiplex cinemas. Therefore, some consider this system not to be practical. They point at the multitude of presets for the many formats that need to be programmed into the projector during installation. Secondly they say that this is not what many strive digital cinema to become: it is not automated to the max. Changing lamp houses requires a projectionist or technician that is able to swap the lamp house between shows. With the prospect of a projection booth without a projectionist in the near future this is not a likely scenario.
However, for smaller cinemas this may well be a solution to consider, as they have plenty of time between screenings and there will always someone able and knowledgeable to change the lamp house.
|Last Updated on Sunday, 15 May 2011 23:33|