GE G8.5 Lamp end of life conditions, Lumen depreciation, End of life cycling, Dimming, Flicker

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.

Typical Warm-up characteristics

	120%
value	100%
	80%
of final
	60%
Percentage	40%			Lamp voltage
				Lamp current
				Light output
	20%
	0%
	0	1	2	3	4

Time from switch-on (minutes)

CMH Lamp performance as a function of supply voltage on a 220V Reference Ballast

130%

Volts

Current

120% Watts

Lumens

110% CCT

LPW

100%

90%
80%
198	209	220	231	242	253

CMH Lamp performance as a function of supply voltage on an electronic ballast

130%

Volts

120% Current

Watts

Lumens

110% CCT

LPW

100%

90%
80%
198	209	220	231	242	253

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 filling 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. Rectification 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 specifically offered for High-Pressure Sodium lamps, where the period of operation is less than 5 minutes, are not suitable for ConstantColor CMH™ lamps.

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 flicker typically of 1.5%, in common with all other discharge lamps. Noticeably lower flicker 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 flicker.

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