Xenon lamps vs mercury vapor lamps

Over the years, Projectors have been evolving at the pace of the latest technological advances in line with the trend towards larger screens and higher resolutions. Digital projectors typically use high-intensity discharge lamps that contain xenon or mercury vapor. Marcos Fernández, Christie's Country Manager for Spain and Portugal, In this article, he highlights the benefits in terms of the performance of the former compared to the latter.

Despite its internal complexity, The function of digital projectors is very simple: Project a large-format image from a video source, Data and graphics on a projection surface; And for this, an internal light source is necessary. Due to the high degree of magnification required by the projected image and the number of optical elements in the path from the light source to the screen, The brightness of the light source must be very high; even more than that radiated by the typical fluorescent and incandescent lamps used in offices and other enclosed spaces.

The two most widespread technologies in digital projection solutions are mercury vapor lamps and xenon lamps. In both cases, The lamp emits light by passing current through a gas subjected to very high pressure (of several hundred atmospheres) inside a fused quartz tube. The current flowing between the electrodes of the lamp (what is called the bow) ignite the gas by making it glow.

The active gas found in mercury vapor lamps is, As its name suggests, mercury heated to a gaseous state that has been mixed with other gases to facilitate start-up, improving its performance and reliability; while, In the case of xenon lamps, the gas used is xenon gas. This basic difference between the two lamp technologies leads us to establish a number of practical differences in terms of the properties and performance of projectors that include these technologies.

Differences in performance

When it comes to performance, The fundamental difference between xenon and mercury vapor lamps lies in the color spectrum of the light they emit. A xenon lamp radiates a fairly flat spectrum with more or less similar intensities at all wavelengths throughout the entire visible range (between 400 nm and 700 nm), approaching the neutral white color of natural light. On the other hand, The typical emission spectrum of mercury vapor lamps is significantly less uniform, showing a series of maximum and minimum peaks throughout the entire visible range, where the highest peak is found in the region of Amarillos. The red end of the mercury vapor spectrum is also on a downward trend compared to the blue end, showing up as a cool white.

The spectrum of upward and downward peaks of the mercury vapour lamp means that projectors with this type of lamp usually offer poorer colour reproduction, vs. projectors that include xenon technology. The measure responsible for determining the accuracy with which colors are reproduced is known as the color rendering index or CRI. In order to improve the IRC, The projector's light path can be designed to better balance the mercury vapour spectrum over the entire visible range and reduce peak height, even if it is at the cost of a considerable drop in the luminous output. Some mercury vapour-based projectors include a motorised yellow separation slot filter that, if necessary, could be placed in the light path to improve the accuracy of the projector's colors, reducing the brightness level as a counterpart.

Another difference in performance between mercury vapor lamps and xenon lamps is the stability of the spectrum over time. The peaked spectrum of mercury vapor lamps involves a considerable change in the color reproduction of a projector, which can be affected as the lamp gets older. On the contrary,, in the case of xenon lamps, The plane spectrum has relatively little effect on color reproduction over time.

Xenon also has a very short-term stability advantage, which manifests itself from the very moment of ignition, maintaining a flat spectrum as it heats up. In addition, It can reach its full brightness capacity in considerably less time than mercury vapor lamps.

Operational considerations

In terms of on-screen performance, Xenon has a clear advantage over mercury vapour. However, The tables are reversed when it comes to assessing traits such as efficiency, the service life and operating cost.

First of all, Mercury vapor lamps are much more effective than xenon lamps at converting electrical energy into light. Indeed, usually, for the same light output, A mercury vapor lamp projector requires less energy to operate than a xenon lamp projector. This will depend on the level to which the light output has been sacrificed for improved colour accuracy (as described above). Projectors that run on less power don't tend to overheat, making them more reliable and quieter.

Secondly, Mercury vapor lamps enjoy a much longer service life, with a minimum duration of 1.000 hours that can reach even the 10.000 depending on the lamp power. While, The life of xenon lamps ranges from 500 hours and a maximum of 4.000.

The combination of high efficiency and long service life means that mercury vapour technology offers the third and decisive advantage: significantly lower operating costs.

Both technologies require very simple maintenance.

Mercury Vapor Lamps, such as Philips' ultra-high-performance UHP lamps and Osram's P-VIP high-quality video projection lamps, are pre-aligned modules that include independent reflectors that are easily replaceable by the user. Perkin Elmer's Cermax xenon lamps are another example of pre-aligned modules. There is another common configuration of xenon lamp, known as a bubble lamp, which can be designed in previously aligned modules, offering the same ease to the user for its replacement and allowing the lamp to be replaced at the factory as many times as necessary.

By containing a small amount of mercury, Mercury vapor lamps require extra care when disposing of an old lamp. Even so, Both types of lamps must be disposed of safely and responsibly in accordance with the environmental requirements for the disposal of this type of waste.

Applications

Given the different advantages and disadvantages of mercury and xenon vapor lamps, It is clear that certain projector applications will be better suited to one type of lamp than the other. Mercury vapour lamps are the best choice when low running costs and the longest possible lamp life are at a premium, while if the priority is to achieve maximum color accuracy and chromatic stability, The best option will be xenon lamps.

Another issue to take into account is the light output required by the projector, which may depend on the screen size and ambient light. Projectors with mercury vapor lamps reach brightness levels that exceed those of traditional models and this seems to be the trend in the future. In fact, Models that include two or more lamps together are considered to offer brightness levels high enough to be used in ProAV applications. However, today, Achieving the highest light output levels in digital projectors is only possible with xenon lamps.

For example, DLP projectors from 3 Christie's M-Series chips are based on mercury vapor lamps and offer a brightness level between 2.500 ANSI lumens and 9.500 ANSI lumens, while the models of 3 Christie chips that include xenon lamps offer a luminous range between the 2.000 ANSI lumens and 30.000 ANSI lumens. Xenon technology is the most logical choice when projecting on large screens or dealing with high ambient lighting.

Projector size is another factor to consider. How mercury vapor lamps are more efficient and consume less energy, Lamp size can be smaller, which in turn has made it possible to develop much smaller projectors. Some are so small that they can fit in a briefcase, leaving even plenty of room. Even so, despite Cermax's tiny xenon lamps and the dwindling dimensions of xenon-based projectors, Mercury vapour has become the technology of choice for small projectors thanks to the advantage of its low cost.

Conclusion

The most important characteristics of each of the lamp types determine the choice of mercury or xenon vapour technology for a particular application. The life of mercury vapor lamps is usually longer than that of xenon lamps and the maintenance costs are lower. In addition, are commonly used in smaller projectors. On the other hand, Xenon technology is the best choice when the highest level of on-screen performance is required, for both brightness and color accuracy. Christie offers a wide variety of digital projectors based on both technologies for every specific need.