vapor lamp is a high intensity discharge lamp. It uses an arc through
vaporized mercury in a high pressure tube to create very bright light
directly from it's own arc. This is different from fluorescents which
use the mercury vapor arc to create a weaker light that mainly creates
UV light to excite the phosphors. The "Merc" as it is known
has been a workhorse for society; lighting streets, factories and large
areas for over 100 years.
- Good efficiency (lamps after 1980s have a high lumen
per watt rating)
- Color rendering is better than that of high pressure sodium street
- Some lamps last far longer than the 24000 hour mark, sometimes 40
- Like many lamps it contains traces of mercury which
must be disposed of properly
- HPS streetlights have a better lumen per watt rating
- Human skin looks green under the light, it is poor for color film/photography
-Warm up time required to start the lamp
20 (clear bulb) 60 (phosphor coated)
*Color Temperature - 6800 K (clear bulb)
*Lumens per watt: 30-60
*Lamp life: 24,000 - 175,000 hours
*Available in 40-1000 W
uses: large areas like parks, street lighting, high ceiling
buildings, gyms. Low pressure lamps with a quartz envelope are
used for germicidal purposes since they allow UV light to pass.
Vapor with phosphor for improved color
is a "Lifegaurd" brand lamp by Westinghouse, it needs
a ballast to run.
UV rays are
produced, but blocked by the borosilicate glass.
There are several
versions of the lamp but the basic principle is the same.
The first mercury
vapor lamps were in a lower pressure tube. One would tip the
lamp, and electrical contacts on each side of the lamp would
send electricity through a liquid mercury which started the
lamp. After that the lamp would heat fast and mercury became
a vapor. The light would intensify as the arc grew stronger
in the tube.
Lamps of today are
high pressure lamps with a fused quartz inner discharge tube.
The high pressure helps increase efficiency and this was developed
in 1936, 35 years after the low pressure lamps came out.
This lamp start with
a small arc between the starting electrode and the main electrode.
This arc goes through argon gas which easily strikes, even in
cold weather. This little arc heats the tube, and over several
minutes the tube gets hot enough to vaporize the solid mercury
stuck to the sides. The mercury vaporized creates a strong light
between the two main electrodes. (see graphic to the left)
To prevent the arc
from infinitely getting stronger a ballast limits the current.
Some lamps are "Self Ballasted", they use an
incandescent filament to act as a resistor, limiting current.
Home lighting fixtures usually use the self-ballasted type where
as the more expensive but more efficient ballasted lamps are
found in large fixtures for municipal lighting.
The photo below
shows a self-ballasted lamp, notice the tungsten filament.
In this clear
bulb zinc and cadmium are metals used along
with the mercury to help color and brightness.
Vapor with a transformer (ballast) build into the base.
bulb at left is just warming up, the bulb at right is after
a few minutes of warming. This bulb has phosphor to help make
the light more of a true white color. It can take several minutes
to warm up.
small amounts of mercury visible on a large discharge tube.\ Right: older heavy ballast for a standard ceiling mounted merc
- Tested mercury vapor arcs in air at common atmosphere
Charles Wheatstone (London) worked with arcs through mercury
during this tests in spectropy. He would create an arc through a metal,
then observe what colors it produced when a prism separated the light
into it's individual frequencies.
- Developed a rudimentary mercury vapor lamp John
Thomas Way (London) Developed a mercury vapor lamp. He tested
them on the Hammersmith Bridge in London.
- Developed an experimental mercury vapor lamp
Leo Arons, (University of Berlin). His lamp worked
fine but had a green blue color that was not acceptable to most
- The First Commercial Mercury Vapor Lamp
Peter Cooper Hewitt (New York City) had a history
of innovations in other fields, and when he set about on the
project of the mercury vapor lamp in 1898 it only took 3 years
to develop the first reliable lamp with a acceptable color of
light. His work was a commercial success and eventually his
company and patents were bought out by General Electric in 1913.
mercury vapor lamp. One would tip the light to get it to start.
These early low pressure lamps used a lot of mercury, today's
lamps use a tiny amount of mercury. Right
around 1900 the mercury arc rectifier was developed, this luminous
device was very important for power conversion. NYC subways
were still using original mercury arc rectifiers to convert
AC to DC power up until the end of the 20th century. (Read more
about the Mercury Arc Rectifier)
Cooper Hewitt mercury vapor tubes and historic fixture
- Higher pressure mercury vapor light in a fuzed quartz tube is developed Kuch
& Retschinsky (Siemens, Munich)
- The modern high-pressure mercury vapor lamp is developed, type MB Philips
(Nederlands) No individual names are available
by M.Whelan with additional research by Rick DeLair
Please contact us if you are a historian and wish to correct or improve
"The General Electric
"A History of Electric Light and Power" by B. Bowers
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