HPS LAMP CYCLING
All HPS lamps experience voltage rise during their life
and have a designed end-of-life voltage rating. When
the voltage rise reaches the end-of-life voltage, the
ballast cannot supply the needed operating voltage, the
lamp goes out, and cycling begins. As the hot lamp
cools, it restarts at a lower than end-of-life voltage. But
as the lamp begins to heat up again, its operating
voltage soon rises past its end-of-life voltage. The lamp
turns O
and the cycle repeats itself.
End-of-life cycling can occur in an HPS lamp at the
time of installation, at six years, at end of life or at any
time in between. A bad lamp can fail prematurely. In
most cases, cycling is caused by a voltage rise due to
increased lamp resistance, electrode wear, etc.
Equipment Mismatching
Using the wrong lamp in the fixture (Figure 17) can cause
cycling. As shown in Table 1, 150-watt HPS lamps are
manufactured in two voltage ratings: 55 volts and 100
volts. HPS 150-watt lamps will have their voltage rating
stamped on the lamp body to avoid confusion when
replacing these lamps. A 150-watt, 100-volt HPS lamp
installed in a 150-watt, 55-volt fixture will cause cycling
because the 55-volt ballast does not supply the
necessary voltage required by the 100-volt lamp.
Using a lower wattage HPS lamp in a higher wattage
fixture, such as a 70-watt lamp in a 150-watt fixture,
also may cause cycling.
Using the wrong or defective ballast or capacitor also
can lead to cycling. Also be sure the ballast and
capacitor are wired correctly.
Reignition Phenomenon
HPS and other HID lamps actually turn ON and O
120 times per second. Current is cut off for a millisecond
or so at each midpoint, or zero crossing point, of the
AC 60 Hertz cycle (Figure 18A). The lamp stays hot
enough to automatically restrike after this very, very
short outage. However, if several cycles of the AC power
are lost or drop out due to loose wire connections or
shorts, the lamp cools sufficiently to turn O
and will
not restrike immediately (Figure 18B).
To avoid dropouts due to poor connections, do not pull
the wires tight when installing the luminaire or its internal
components such as the ballast, photocontrol, starter
or capacitor. The lamp must be screwed into the socket
properly to make a good connection. The coil spring
must be compressed completely to make proper
contact at the base of the socket. All of the metal on
the lamp�s screw base should be hidden below the rim
of the socket when the lamp is screwed in completely.
The lamp socket center contact and the tip of the lamp
base must be in proper contact when the lamp is
installed. If the center contact and lamp tip become
misaligned due to a mismatch between the socket
contact and the lamp tip, the lamp may not start due to
poor or partial contact between the two. If this problem
occurs, some service technicians may try turning the
lamp out 1/2 turn or so. In some cases, the lamp may
now light, but this is not an acceptable solution to the
problem. The connection between the lamp and socket
is not under full spring pressure, and electrical arcing
will occur, drastically reducing lamp life or resulting in
socket burnout.
Vibration Sensitivity
HPS lamps nearing the end of their service lives are
very vibration sensitive. Vibration causes a rise in lamp
current above the end-of-life voltage. HPS light color
gives a good indication of relative lamp age. Older HPS
lamps give off a whiter light. The color rendition they
produce actually is better than new HPS lamps.
Vibration in the lamp due to wind or traffic can cause
the lamp to cycle. Vibration-induced cycling is common
in fixtures mounted on bridges. You can simulate this
vibration in a burning lamp by striking the mounting
pole with a short length of lumber, or by actually
bumping the light fixture or light bulb with your hand. If
the lamp turns O
when the pole is struck, it is
probably vibration sensitive.
The bump test also is a good way to check for intermittent
open circuits and poor connections in the lamp and fixture.
For example, the lamp�s internal mounting frame is
designed to allow the arc tube to move as it expands
and contracts with changes in temperature. The metal
mounting frame is stable, but the arc tube connects to
the lamp base through the use of a flexible bond strap.
Over time, the bond strap weld can fail, causing
intermittent contact. A bump test often will detect this
type of failure.
Keep in mind that normal end-of-life cycling is marked
by a more or less predictable on/off pattern of a minute
or so ON and a minute or so O
. Cycling caused by
open contacts or bad welds is much more
unpredictable. The lamp may stay ON or O
for
several minutes or several hours.
When you field test a lamp with cycling problems,
remember to test the photocontrol operation. As the
lamp starts to come up, bump it to see if you can make
it cycle O
. You may even be able to see the slight
electrical arcing at the bad connection. You also should
bump test the lamp after it has started and stabilized.
Thermal Cycling
Thermal cycling is another vibration- or movementinduced
problem that occurs in HPS lamps. Thermal
blink-out is most common in exterior reservoir lamps
operated in a position that places the amalgam reservoir
above horizontal in the light fixture. However, severe
vibration problems can cause thermal cycling in all types
of HPS lamps. Vibration or movement due to wind,
traffic or other reasons can cause excess amalgam to
splash down onto the white-hot electrode, giving it a
thermal shock. This thermal shock causes the lamp to
drop out and cycle.
Bridge and viaduct installations are prone to thermal
cycling problems. Thermal cycling can be avoided by
selecting nonexternal reservoir-type lamps for highvibration
applications. In severe vibration conditions,
thermal cycling could be fixture related. You can test
for thermal cycling using the bump test.
Photocontrol-Induced Cycling
An overly sensitive photocontrol unit may cause cycling
in an HPS or HID lamp installation. Light from the
luminaire, or from other light sources around it, can
trick the photocontrol causing it to turn O
the
luminaire. Aim the photocontrol away from strong light
sources, or install shields to cut down on the level of
ambient light entering the photocell (Figure 19).
Seasonal changes can cause cycling problems due to
reflective light differences between green leaves in
spring and summer, and dead leaves and exposed tree
bark in fall and winter.
much appreciated... Weird thing is I see nothing wrong with the bulb it self... Looks brand new still.... ?!? 
