HQA Clear Bulb Mercury Discharge

Dating back to the mid 1960's, mercury lamps such as this were still required in small quantities without the fluorescent phosphor coating which had become standard on all lamps many years earlier.

Principally they were employed in streetlighting applications which had been designed with a long spacing between each lighting column, frequently encountered in many continental European countries, and where the good optical control attainable with clear lamps was required to throw the light uniformly across a wide area. It had been found that retrofitting the later colour-corrected phosphor coated lamps into the same luminaires did not achieve such good optical control, and unlit patches of road could occur in between the very brightly lit areas under each lantern. Thus until new lanterns were also installed which were better suited to distributing the light of coated lamps, a small but significant requirement still remained for the earlier clear versions.

It is interesting to note the extensive whitening of the arc tube in this early lamp, which has completed many years of service. The rapid lumen depreciation of mercury lamps has been a drawback since their earliest days, but during the 1950's a tremendous amount of research went into preventing the arc tube blackening which caused this. GE of America was first to introduce a non-blackening arc tube, and this Osram lamp is made along the same lines. A physically larger electrode which runs cooler is found at each end of the arc tube, and in addition the chemistry of the electrode and its emitter coating has been modified such that deposits on the arc tube wall appear white instead of black, thus helping to avoid such rapid lumen depreciation.
Manufacturer: Osram GmbH
Lamp Power: 125 Watts
Lamp Current: 1.15 Amps
Lamp Voltage: 125 Volts
Cap Type: E27s/30 Ni plated brass + vitrite
Bulb Finish: Clear Soda-lime soft glass
Bulb Type: ED-75 ED-23½ in eighths/inch
Overall Length: 170 mm 6¾ inches
Light Centre Length: 110 mm 4 3/8 inches
Arc Length: 25mm 1 inch
Electrodes: Backwound tungsten Double carbonate emitter
Atmosphere: Inner: Hg | Ar (8 atm) Outer: Nitrogen
Luminous Flux: 5,250 lm @ 100 hrs
Luminous Efficacy: 42.0 lm/W @ 100 hrs
Colour Temperature & CRI: CCT: 6000K CRI: Ra 16
Chromaticity Co-ordinates: CCx: 0.315 CCy: 0.380
Burning Position: Universal Horiz. lumens 10% less
Rated Lifetime: Not published
Warm-up & Re-strike Time: 3 minutes 5 minutes
Factory: Berlin Germany
Date of Manufacture: May 1965 Date Code: mdY
Original & Present Value: Unknown
References: 1) Siemens-Osram German Lamp Catalogue, 1960.