ConstantColor CMH Double Ended

Product information

Double Ended Ceramic Metal Halide Lamps

35W, 70W and 150W

ConstantColor™ CMH lamps combine the HPS technology (providing stability, efficiency & uniformity) and the Metal Halide Technology (providing bright white quality light) to produce highly efficient light sources with good colour rendering and consistent colour performance through life. This is achieved by using the ceramic arc tube material from the Lucalox™ lamp, which minimises the chemical changes inside the lamp through life. When combined with the halide doses used in Arcstream™ Metal Halide lamps then the quality and stability of the dose maintains the colour consistency. Hence the name ConstantColor™ CMH.

Metal halide lamps, traditionally made with quartz arc tubes, are prone to colour shift through life and lamp-to-lamp colour variation. Some of the dose, e.g. sodium, (an important component of metal halide lamps), can migrate through quartz to cause colour shift and loss of light through life. The ceramic arc tube resists this material loss, can be manufactured to tighter tolerances and withstands a higher temperature to provide a more constant colour.

Applications areas

  • Retail
  • Offices
  • City beautification
  • Architectural lighting
  • Display Cabinet
  • Hotels


  • Consistent colour over life
  • Colour uniformity lamp to lamp
  • Bright light – in a very compact size
  • Excellent colour rendition
  • Improved reliability due to 3 part design
  • Up to 97 LPW efficacy
  • 15,000 Hr life
  • UV control
  • Easy retrofit for Quartz Metal Halide lamps
  • 3000K and 4200K colour temperature

Specification Summary

Wattage [W] 35 70 70 150 150
Format Double Ended
Bulb type T6 T6 T6 T7 T7
Bulb diameter [mm] 20 20 20 24 24
Bulb material UVC Quartz
Bulb finish Clear
Arc Gap [mm] 4.65 7.6 7 11 10
Base RX7s RX7s RX7s RX7s-24 RX7s-24
CCT [K] 3000K 3000K 4200K 3000K 4200K
CRI [Ra] 80+ 80+ 90+ 80+ 90+
Burning position HOR ± 45°
Luminaire characteristics Enclosed
Initial Lumens [lm] 3400 7000 6200 14500 12500
Lamp voltage [V] 90 90 90 96 96
Lamp current [A] 0.5A 0.98A 0.98A 1.8A 1.8A



Wattage [W] 35 70 70 150 150
A [mm] maximum 118 118 118 135.4 135.4
B [mm] nominal 20 20 20 24 24
C [mm] nominal 57 57 57 66 66


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 survival.


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 70-400Hz, eliminating perceptible flicker.

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.

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.

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