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Warm-up characteristics
During the warm-up period immediately after starting,
lamp temperature increases rapidly evaporating
mercury and metal halide dose in the arc-tube.
Lamp electrical characteristics and light output stabilise
in less than 4 minutes. During this period light output
increases from zero to full output and colour
approaches the final visual effect as each metallic
element becomes vaporised.
Supply voltage sensitivity
Supply line voltage to conventional magnetic ballast control
gear should be as close to the rated nominal value as
possible. Lamps will start and operate at 10% below rated
supply voltage but this should not be considered as a normal
operating condition. In order to maximise lamp survival,
lumen maintenance and colour uniformity, supply voltage
and rated ballast voltage should be within ±3%. Supply
variations of ±5% are permissible for short periods only.
Where large supply voltage variation is likely to occur, use
of electronic control gear, which is designed to function
correctly for a voltage range typically 200-250V, should be
considered.
120%
100%
80%
60%
40%
20%
0%
1
0
2 3 4
Time from switch-on (minutes)
Typical Warm-up characteristics
Lamp voltage
Lamp current
Light output
Percentage of final value
130%
120%
110%
100%
90%
80%
209
198
220 231 242 253
CMH Lamp performance as a function of supply
voltage on a 220V Reference Ballast
Volts
Current
Watts
Lumens
CCT
LPW
Volts
Current
Watts
Lumens
CCT
LPW
130%
120%
110%
100%
90%
80%
209
198
220 231 242 253
CMH Lamp performance as a function of supply
voltage on an electronic ballast
Dimming
In certain cases, dimming may be acceptable, subject to further testing. Contact your GE representative for more information.
Large changes in lamp power alter the thermal characteristics of the lamp resulting in lamp colour shift and possible reduction
in lamp through life survival.
Flicker
When ConstantColor CMH™ lamps are operated from a conventional magnetic ballast there will be 50Hz line frequency light
output icker typically of 1.5%, in common with all other discharge lamps. Noticeably lower icker levels occur when lamps
are operated horizontally.
Flicker levels of 1.5% do not normally cause concern to the end user, but use of electronic control gear should be considered
where visual comfort and performance is critical. Suitable electronic ballasts for ConstantColor CMH™ typically provide square
wave operation in the range 70-200Hz, eliminating perceptible icker.
Lamp end of life conditions
The principal end-of-life failure mechanism for CMH™ lamps is arc tube leakage into the outer jacket. High operating
temperature inside the arc-tube causes metal halide dose material to gradually corrode through the ceramic arc tube wall,
eventually resulting at normal end-of-life in leakage of the lling gas and dose. Arc-tube leakage into the outer jacket can be
observed by a sudden and significant lumen drop and a perceptible color change (usually towards green).
The above situation is often accompanied by the so-called rectification phenomena. This occurs where a discharge is
established between two mount-frame parts of different material and/or mass, causing asymmetry in the electrical
characteristic of the resulting discharge current. Rectication can lead to overheating of the ballast, therefore conventional
magnetic ballasts must conform to requirements of the IEC61167 lamp standard by incorporating protection to maintain
safety and prevent damage.
It is good practice when lamps are operated continuously 24 hours per day, 7 days per week to introduce switching
once every 24 hours. Lamps with one electrode failing often will not restart and can therefore be easilly detected and replaced.
Lumen depreciation
All metal halide lamps experience a reduction in light output and slight increase in power consumption through life.
Consequently there is an economic life when the efficacy of lamps fall to a level at which is advisable to replace lamps and
restore illumination levels. Where a number of lamps are used within the same area it may be well worth considering a group
lamp replacement programme to ensure uniform output from all the lamps.
End of life cycling
A condition can exist at end-of-life whereby lamp voltage rises to a value exceeding the voltage supplied by the control gear. In
such a case the lamp extinguishes and on cooling restarts when the required ignition voltage falls to the actual pulse voltage
provided by the ignitor. During subsequent warm-up the lamp voltage will again increase, causing extinction. This condition
is known as end-of-life cycling. Normally cycling is an indication that lamp end-of-life has been reached, but it can also occur
when lamps are operated above their recommended temperature. Lamp voltage at 100 hours life should not increase by more
than 5V when operating in the luminaire, when compared to the same lamp operating in free-air. A good luminaire
design will limit lamp voltage rise to 3V.
It is good practice to replace lamps that have reached end-of-life as soon as possible after failure, to minimise electrical
and thermal stress on ignitor internal components. The use of a ‘timed’ or ‘cut-out’ ignitor is not a specific requirement for
ConstantColor CMH™ lamps, but is worth considering as a good optional safety feature which also prolongs the life of ignitor
internal components, lamp holder contact surfaces and fixture wiring.
The operating period of a timed/cut-out ignitor must be adequate to allow lamps to cool and restart. A period of 10 to 15
minutes continuous or intermittent operation is recommended before the ignitor automatically switches off. Timed/cut-out
ignitors specically offered for High-Pressure Sodium lamps, where the period of operation is less than 5 minutes, are not
suitable for ConstantColor CMH™ lamps.