Choosing between mercury-vapor
and Xenon lamp technologies
Technology brief
Overview
Digital projectors, despite their internal complexity, have only one
function — to project a large image from video, data and graphics
sources onto a viewing surface. In order to do this they need an
internal light source. Because of the large degree of magnification of
the projected image and the number of optical elements in the path
from light source to screen, the light source needs to be extremely
bright — far brighter than the familiar incandescent and fluorescent
lamps used to illuminate offices and other internal spaces.
consequence of a mercury-vapor lamp’s spiky spectrum the color
rendition of a projector can change noticeably as the lamp ages.
The flat spectrum of a Xenon lamp, in contrast, results in relatively
little color shift over time.
Xenon even has a stability advantage in the very short term just
after turn on, maintaining its flat spectrum as it warms up. It also
reaches full brightness in far less time than a mercury-vapor lamp.
The two lamp technologies most commonly used in digital
projectors today are mercury vapor and Xenon. Both types of lamp
generate light by passing current through a gas under very high
pressure (up to several hundred atmospheres) within a fused quartz
envelope. The current flowing between the lamp’s electrodes —
called an arc — ignites the gas and causes it to glow.
The active gas in mercury-vapor lamps is (as the name suggests)
mercury heated to a vapor state mixed with other gases to enable
start-up and to improve performance and reliability. Xenon lamps, on
the other hand, use Xenon gas. This fundamental distinction between
the two lamp technologies leads to a number of practical differences
in the properties and performance of projectors that use them.
Performance differences
The primary performance difference between mercury-vapor and
Xenon lamps is in the color spectra of the light they emit. A Xenon
lamp emits a fairly flat spectrum with more-or-less equal intensities
at all wavelengths throughout the visible range (roughly 400 nm
to 700 nm), which approximates the neutral white color of natural
daylight. The emission spectrum typical of mercury-vapor lamps,
on the other hand, is considerably less even, exhibiting a number
of strong peaks and valleys throughout the visible range, with the
strongest peak in the yellow region. The red end of the mercuryvapor spectrum also tends to be low compared to the blue end,
visible as a cool white (See Figure 1.).
As a result of mercury-vapor’s up-and-down spectrum, projectors
that use these lamps typically exhibit poorer color rendition than
those that use Xenon lamps, as measured by a metric known as the
color-rendering index (CRI). In order to improve the CRI a projector’s
light path can be designed to better balance the mercury-vapor
spectrum across the visible range and reduce the size of the peaks,
but at the cost of a considerable drop in light output. Some mercuryvapor based projectors feature a motorized yellow-notch filter that
can be positioned (as required) in the light path to improve the
projector’s color accuracy, with reduced brightness as the trade off.
Another performance difference between mercury-vapor and
Xenon lamps is the stability of the spectrum over time. As a
Figure 1. — Xenon vs mercury spectrum comparison
Operational considerations
Xenon clearly has an edge
over mercury vapor with
respect to on-screen
performance. However, the
tables are turned when it
comes to considerations such
as efficiency, useful life and
operating cost.
First, mercury-vapor lamps
are considerably more
efficient than Xenon lamps at
converting electrical power
into light. For a given light
output, a projector with a
mercury-vapor lamp usually
Figure 2. — Lamp types
operates at a lower power than a
projector with a Xenon lamp (depending on the degree to which
light output has been sacrificed for better color accuracy — see
above). A lower power projector typically runs cooler, which is
good for reliability, as well as quieter.
Second, mercury-vapor lamps also have a much longer useful
life, ranging from about 1,000 hours to as many as 10,000 hours
depending on lamp power. In comparison, the useful lifetimes
of Xenon lamps vary from over 4,000 hours down to just 500
hours. The one-two punch of higher efficiency with longer life
also gives mercury vapor a much lower operating cost — the
third advantage.
Xenon lamps range from 2,300 ANSI lumens up to 32,500 ANSI
lumens. Xenon is the natural choice when illuminating very large
screens or combating high ambient illumination.
Projector size is another factor. Since mercury-vapor lamps are
efficient and consume less power the size of the lamp can be
smaller, which in turn has enabled the creation of very small
projectors; some small enough to fit in a briefcase with room to
spare. Even though small CERMAX Xenon lamps do exist and
Xenon-based projectors in general are getting smaller every
year, mercury-vapor’s cost advantage has made it the preferred
technology for these smaller projectors.
Ease of maintenance is similar for both lamp technologies.
mercury-vapor lamps such as Philips’ UHP® (Ultra High
Performance) and Osram’s P-VIP® (Premium Video Projection)
are pre-aligned modules with self-contained reflectors that can
be easily user replaced. CERMAX® Xenon lamps
from Perkin Elmer are also pre-aligned modules.
The other common Xenon lamp configuration,
called a bubble lamp, can be engineered into
White color balance
pre-aligned modules, which confers the same
Colour Rendering Index
ease of user replacement and allows re-lamping
(CRI)
in the factory multiple times.
When it comes time to dispose of an old lamp,
mercury-vapor lamps do require somewhat more
care because they contain a small amount of
mercury. However, both types of lamp should
be disposed of in a safe and environmentallyresponsible manner.
Applications
Since mercury-vapor lamps and Xenon lamps
have different strengths and weaknesses some
projector applications naturally favor one type
over the other. Mercury-vapor lamps are best
used when low operating cost and long lamp
life are the most important factors, while Xenon
should be used when color accuracy and color
stability over time are the priorities.
Worldwide offices
Christie Digital Systems USA, Inc
USA – Cypress
ph: 714 236 8610
United Kingdom
ph: +44 (0) 118 977 8000
Christie Digital Systems Canada Inc.
Canada – Kitchener
ph: 519 744 8005
Germany
ph: +49 2161 664540
France
ph: +33 (0) 1 41 21 44 04
Spain
ph: +34 91 633 9990
Mercury-vapor
Neutral white (~6100K)
Cool white (~8000K~8500K)
>95
~60
Good
Lower
Color saturation
Wattage ranges
300W – 6kW
100W – 350W
Efficiency
–30 – 40 lumens/W
–60 lumens/W
Approximate list costs
$8 – $28/(1000 lm)
$7 – $9/(1000lm)
110 VAC (1kW), 220 VAC (>1kW)
110 VAC (dual lamp)
<15s to full brightness
60s to full brightness
500hr – 4000hr
1000hr – 10,000hr
Higher
Lower
Good to very good
Good
Projector size
Larger
Smaller
Projector weight
Higher
Lower
Power requirement
Warm-up time
Lifetime
(depends on lamp power)
Audible cooling noise
Ruggedness
Figure 3. — Lamp type comparison
Another consideration is the light output required from the
projector, which can depend on screen size and ambient lighting.
Projectors with mercury-vapor lamps are much brighter than
they have been traditionally, a trend that can be expected to
continue into the future. In fact, models that use two or more
lamps in tandem are now considered bright enough for Pro AV
applications. However, the highest light outputs available from
digital projectors today are only possible using Xenon lamps.
For example, Christie® M Series 3-chip DLP® projectors based on
mercury-vapor lamps range in brightness from 5,700 ANSI lumens
to 10,500 ANSI lumens while the Christie 3-chip models that use
Corporate offices
Xenon
Conclusion
Choosing between mercury-vapor and Xenon lamp technologies
for a given application depends on the essential characteristics of
each lamp type. Mercury-vapor lamps typically last longer than
Xenon lamps and cost less to maintain. They are also commonly
used in smaller projectors. Xenon, on the other hand, is the
best choice when the highest level of on-screen performance is
required, both for brightness and color accuracy (See Figure 3.).
Whatever the requirement, Christie offers a wide range of digital
projectors based on both technologies.
Independent sales
consultant offices
Eastern Europe and
Russian Federation
ph: +36 (0) 1 47 48 100
United Arab Emirates
ph: +971 (0) 4 299 7575
India
ph: (080) 41468940
Singapore
ph: +65 6877 8737
China (Shanghai)
ph: +86 21 6278 7708
Italy
ph: +39 (0) 2 9902 1161
China (Beijing)
ph: +86 10 6561 0240
South Africa
ph: +27 (0) 317 671 347
Japan (Tokyo)
ph: 81 3 3599 7481
Korea (Seoul)
ph: +82 2 702 1601
For the most current specification information, please visit www.christiedigital.com
Copyright 2011 Christie Digital Systems USA, Inc. All rights reserved. All brand names and product names are trademarks, registered trademarks
or tradenames of their respective holders. Christie Digital Systems Canada Inc.’s management system is registered to ISO 9001 and ISO 14001.
Performance specifications are typical. Due to constant research, specifications are subject to change without notice. Xe-Hg Lamp Tech Nov 11