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High Intensity Discharge sources are another light source that have been with us for some time



HID Light Sources, Ever hear of Non-Passive End of Life?
By
Darrin Hoyle, IESNA
dhoyle@cooperlighting.com


or how about Spontaneous De-construction? Those are some of the terms that are used if a
mistake is made when mating lamps and ballasts together on some High Intensity Discharge
(HID) systems. In other words, the lamps could explode! It is essential when dealing with HID
sources, especially some of the newer Pulse Start systems, that lamps and ballasts be designed
to work together. HID sources have been with us for some time, with the oldest, Mercury Vapor,
being utilized in street lighting since 1933. While the original lamp introductions had poor color
temperature and color renderings, some newer technologies, such as Ceramic Metal Halide, are
suitable for high end retail applications. High Intensity Discharge sources combine the point
source nature of the arc tube which supports precise optical design (it is easier to create
dramatic punches of light designed around smaller physical light sources, hence the popularity of
incandescent) and the energy efficiencies of fluorescent systems. So not only is it possible to
provide dramatic lighting effects, but it is also possible to get 10,000 hours of life or better.
However, most HID systems are not Ceramic Metal Halide. In fact the most popular HID systems
are High Pressure Sodium or Probe Start Metal Halide. Typically found in high wattage
applications (175w and above) they are commonly situated in exterior applications (i.e. parking
lots) or in high ceiling applications (i.e. warehouses). A versatile and flexible lighting system, HID
sources have been around for a long time and continue to prove themselves a viable solution to
todays complex lighting challenges.

There are four major families under the HID umbrella. They are Mercury, Low Pressure Sodium
(though not technically a HID source, well discuss that in a moment, it is often referred to as
being one), High Pressure Sodium and Metal Halide. Metal Halide can further be broken down
into Probe Start (or standard Metal Halide), Pulse Start and Ceramic Metal Halide. All of these
are systems, meaning that they require a ballast and a lamp to work, just like fluorescent
lighting. While HID is an ideal choice for many applications, there are some problems and
limitations associated. First, several of the systems have a significant depreciation in light output
over the course of their life. While most light sources have some depreciation, many HID sources
can loose up to forty percent of initial lumens. To compensate for this, a mean lumen calculation
is critical and must be adhered to during the design phase. Mean, or design lumen information is
typically found in the lamp manufacturers catalogue. A secondary issue primarily associated with
Metal Halide is color shift. The color of the lamp may change drastically over the course of the
lamps life, plus or minus 600 Kelvin, which is very visible in most applications.

A trend to Electronic ballasts, again primarily, although not exclusively, in Metal Halide systems is
largely eliminating the color shift problems. They also draw considerably less power to operate
(called ballast losses) than magnetic ballasts, and so the system as a whole is more efficacious.
Electronic ballasts are lighter and easier to handle, and can enhance lamp life as well. While
prohibitively expensive in higher wattages, there are a variety of lower wattages available and
there are some applications which do justify the expensive of a 400W electronically ballasted
system.

Mercury and Low Pressure Sodium are sources that are seldom specified today. They are an old
technology that has largely been surpasses by newer light sources. Each does have a few
advantages though, and so they are still found in some areas. Mercury does not die at end of
life the way an incandescent or a fluorescent would, it simply gets dimmer, and dimmer and
dimmer. For this reason, some like to use this source in areas that are very remote or rarely
accessed as there will almost always be some light in the space. Also, Mercury has reached a
very low cost point, and so some low price area lights utilize it.

Cooper Lighting, Inc. - 1121 Highway 74 S- Peachtree City, GA 30269 Submitted
9/30/2003
1




Cooper Lighting, Inc. - 1121 Highway 74 S- Peachtree City, GA 30269 Submitted
9/30/2003
2

Low Pressure Sodium is technically not a High Intensity Discharge light; however it is usually
categorized with the other true HID sources because the applications for it are similar. It is
numerically one of the strongest light sources available today. In some configurations it may
generate as much as 140 LPW with an 18000 hour life. Low Pressure Sodium has a color
temperature of around 1800 Kelvin and a CRI of 0 (many consider CRI not to apply to the LPS
source). The very low temperature and CRI of this source does a poor job of illuminating objects,
and so even though it is numerically very strong, the reality is most applications would seem dark
if lit with this source. It has recently made a small come back in some areas due to Dark-Sky
(
www.darksky.org
) and as a turtle friendly light. In some costal areas where turtles and reptiles
breed and nest, Low Pressure Sodium light sources are utilized because it has minimal impact on
the animals habits.

High Pressure Sodium is a commonly utilized light source for exterior applications that is used for
a variety of reasons, most notably because it has a long life (24000 hours or more) and it can
produce around 97 LPW. While not as many lumens as the Low Pressure Sodium source, the
slightly better color rendering (around 22) and color temperature (2200) make this a more
acceptable choice. Many Utility companies prefer High Pressure Sodium because of the lower
maintenance costs associated with the lamp. High Pressure Sodium lamps may cycle at end of
life. A way to avoid this is to use a Non-cycling igniter (part that starts the lamp), or to switch to a
non-cycling lamp. There are also lamps that change color as they age, indicating when it is time
to replace them.

Metal Halide systems break into three families. Probe Start, Pulse Start and Ceramic Metal
Halide. Probe Start, or standard metal halide, is the oldest of the three families. With a color
rendering of 65-70 and color temperature 3000-4100K, Metal Halides are utilized in both interior
and exterior applications. A 400W Probe Start Metal Halide has around 53 LPW maintained.
The lamp contains a starting Probe (hence Probe Start) and the system does not utilize an igniter.
This is the oldest, least expensive and most commonly used type of Metal Halide System.

Pulse Start Metal Halide requires a different ballast system than Probe start metal halide, which
prevents these systems from being compatible. It is important to note that both Probe Start and
Pulse Start are exclusive, system approaches that cannot be interchanged. Pulse Start uses an
igniter located inside the ballast pod to start the lamp instead of the starting probe utilized by
standard, probe start metal halide. The color temperature and CRI of a Pulse Start system are
virtually unchanged from a Probe Start system, but Pulse Start offers less color shift, faster warm
up and restrike times, less lumen depreciation, higher initial lumens and in some cases longer
life. Really, a good way to describe Pulse Start is more light output for the same energy input. A
400W Pulse Start lamp generates around 73 LPW, which is a significant improvement over older
technologies.

The newest form of Metal Halide is high wattage Ceramic Metal Halide. Ceramic Metal Halide
operates on a Pulse Start ballast. The biggest advantage Ceramic Metal Halide offers over Pulse
Start is better Color Rendering. The CRI of a 400W Ceramic Metal Halide is around 92-94. This
is much better than any other HID system available and a real advantage for many end users
including Retailers, Quality Control and Manufacturing. Very popular in the lower wattages, new
high wattage ceramic lamps are just starting to gain popularity.

HID sources are a versatile and flexible approach to lighting. Although there are limitations to the
systems, they are advantageous in many respects. They are ideal for hot or cold applications,
they are easy to design optics for because of their smaller light center and they offer long life.
While they will not work with the emergency battery packs that can be utilized with fluorescent or
incandescent systems, they do work with inverters or generators, depending on how the electrical
engineer wants to layout his or her design. Whether in a retail application, or a warehouse, or a
parking lot, HID sources continue to prove themselves a viable choice for todays lighting
environments.