Lamps were first produced commercially by Philips in Holland in
1932. There are two kinds of sodium lights: Low Pressure (LPS) and High
Pressure (HPS). These lamps are mostly used for street lighting
as well as industrial uses.
lamp works by creating an electric arc through vaporized sodium metal.
Other materials and gases are used to help start the lamp or control
its color. See the photos lower on this page for more details.
credits and sources are located at the bottom of each lighting page
LPS lamp was the first sodium lamp to be developed. It is known by its
signature monochromatic yellow color. It is mostly used in Europe since
it did not appeal in other markets due to its poor CRI or color rendering.
It is among the most efficient lamps in the world because it uses all
the current it gets to create light at the most sensitive color (frequency)
to the human eye. An incandescent lamp in contrast creates light at
all frequencies from Infrared (non-visible) to UV at the other end of
the spectrum. The energy used to make non-visible light is a waste of
energy since it does not help do the principle job of an electric light.
The LPS lamp is also called a SOX lamp (SO for sodium)
Very efficient lamp
- Powerful lamp for use of large areas
- Despite a warm up time of 5-10 minutes it restarts immediately if
there is a brownout
- Lumen output does not drop with age (such as in LEDs or incandescents)
- Worst color rendering of any lamp
- Sodium is a hazardous material which can combust when exposed to air
(such as if the bulb is broken in the trash)
Color Temperature: 1800
100-190 lumens per watt
Bulb life: 18,000 hrs
Common Uses: Outdoor lighting, security lighting, long tunnel lighting
(the light seems to give less fatigue in tunnel driving than white lights
flashing by at close proximity).
LPS Lamp is mostly in Europe for outdoor lighting. They create a monochromatic
yellow light. In the diagrams below you will see how as it starts it
creates a red glow due to the neon gas. The neon gas lights at a lower
temperature. As the temperature increases the sodium begins to vaporize
and the lamp turns to a pure yellow.
An LPS with it's yellow glow
a lower glow voltage, argon helps the smaller lamps start at a lower
voltage. The larger LPS lamps used in street lighting for the most part
do not use argon.
2. LPS Development
pressure sodium lamps were invented first in 1920 by Arthur H. Compton
at Westinghouse. The first lamp was a round bulb with two electrodes
on each side. The solid sodium metal remained on the bottom center of
the bulb. When heated up the metal would vaporize and the lamp would
glow yellow. The lamp had to be designed in a sphere because after the
metal cooled when the lamp was turned off, the sodium has a property
of migrating to the coolest part of the bulb where it solidifies. A
tube design would be more particle, similar to the neon lamp which had
already been developed by 1920, but it was found that the sodium would
migrate to the outer ends of the tube, and there the sodium would destroy
the electrodes over time as well as not get hot enough to vaporize.
The problem with Compton's models is that the highly corrosive sodium
would attack and blacken regular silica glass.
Pirani led the next major advancement in the low pressure
sodium lamp. He worked for Osram in Germany where he developed
a sodium-resistant glass in 1931. He used an oven to heat the
lamp, which vaporized the sodium and started the lamp.
1932 - The first
sodium lamps for commercial sale were made by Philips. Philips has not
released the names of the individuals who did the monumental work of
developing a reliable sodium lamp ready for widespread use. The first
lamps had a removable outer jacket with a vacuum between glass to insulate
the bulb to keep it hot enough to keep the sodium in vapor form.
the outer vacuum jacket as a bulb with the inner discharge tube inside,
therefore eliminating the separate outer jacket and improving insulation
coating on the inside of the outer jacket to reflect infrared (heat)
waves back to the bulb, keeping it warmer and improving reliability
in cold weather.
Pressure Sodium Lamp (HPS Lamp)
The HPS lamp is the most
ubiquitous lamp for street lighting on the planet. The lamp is an improvement
over the LPS lamp in that it has more acceptable color with the great
efficiency of the sodium lamp. The better color rendering comes with
a bit of sacrifice, it has less efficiency than the LPS. General Electric
first developed the lamp in Schenectady, New York and Nela Park, Ohio.
The first lamp came on the market in 1964.
HPS lamp with a starting strip, it uses a xenon starting gas.
-Good efficiency (lumens per watt)
-Smaller size than LPS or fluorescent, the HPS fits into many
-Can be retrofitted into older Mercury Vapor fixtures
-Better bulb life than LPS lamps
-Still has a bad color rendering compared to metal halide and
-Requires a lossy ballast (inefficient) that operates a low arc
voltage of 52-100V. This reduces the actual efficiency of the
lamp when you count the whole system together.
Bulb Life: 24,000
lighting, municipal lighting, home yard lighting, high bay lighting
HPS lamp consists of a narrow arc tube supported by a frame in a bulb.
The arc tube has a high pressure inside for higher efficiency. Sodium,
mercury and xenon are usually used inside the arc tube. The arc tube
is made of aluminum oxide ceramic which is resistant to the corrosive
effects of alkalis like sodium.
The lamp comes in variations,
but the most common way to start the lamp is with a pulse start.
There is an ignitor built into the ballast which sends a pulse
of high voltage energy through the arc tube. This pulse starts
an arc through the xenon gas. The lamp turns sky blue as the xenon
lights. The arc then heats up the mercury and the mercury vapor
then lights, giving the lamp a bluish color. The lamp heats and
the sodium is the last material to vaporize. The sodium vapor
strikes an arc over 240 C. The sodium is mixed with other impurities
to create a more "white" light. The mercury helps add
a blue spectrum light to the pure yellow of the sodium.
a vacuum is difficult, oxygen and other gasses can seep in over time.
The getter keeps a stable vacuum by sucking out remaining oxygen
and unwanted gasses. The sodium is stored often stored in the amalgam
reservoirs on the ends of the arc tube when it is cool unlike the LPS
lamp where the sodium is stored in the bumps on the side of the tube
(see LPS diagrams)
Sodium in these lamps is a highly volatile substance. When exposed to
air the sodium may explode. The sodium lamp should not be disposed of
in normal the normal garbage disposal. There have been many cases of
garbage trucks catching fire when the bulbs in the back broke. Sodium
lamps also contain mercury. The newer LPS lamps contain less mercury
than before, but this has effected performance negatively.
of HPS Lamps
inventors of the sodium lamp knew that with a higher pressure in the
arc tube that better efficiency could be achieved. The problem was that
there was no material that could stand the high pressure, high temperature,
and corrosive properties of sodium.
Finally, 35 years after Compton invented the sodium lamp an
ideal material was discovered for making an HPS lamp. A researcher
named Robert L. Coble working at the General Electric Research
Lab near Schenectady, New York developed a material called Lucalox.
Lucalox was a commercial term for aluminum oxide ceramic.
His work helped pave
the way for William Louden, Kurt Schmidt, and Elmer Homonnay
to invent the HPS lamp.
Louden, Schmidt and Homonnay worked to create a HPS lamp at Nela Park,
Ohio (A General Electric research park in Cleveland, OH). Using the
new Lucalox material they figured out how to create an arc tube, evacuate
the tube, and insert electrodes that would withstand the hostile conditions
inside the tube. The first commercial release of the lamp was in 1964.
In the 1980s GE engineers further improved the lamp life and efficiency.
Louden, Schmidt and
Homonnay with a prototype light
video of probably the only remaining 1960s HPS prototypes in the world.
It was saved from being disposed of at the GE research lab in Niskayuna,
by M.Whelan with additional research by Rick DeLair
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The Subdivision of the Light by Unknown
History of Electric Light and Power" by B. Bowers
Westinghouse lamp catalogues from 1901-1903
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