GE H100A38/A23 High Pressure Mercury
In North America and Japan, it is interesting that a significant market remained for clear mercury discharge lamps long after the introduction of the improved types having fluorescent outer bulbs. At the time of the introduction of the coated lamp this was understandable because they were considerably more expensive than uncoated predecessors.

The principal technical reason for the continued use of clear lamps is that they work better in the optical systems of many lanterns. With the fluorescent coated lamps, the entire bulb surface is the point of light emission and the large source area means that the light is not so easy to control in optical systems. Light from a lantern is thrown out at a much wider angle and although a greater area is illuminated, the intensity at any given point is considerably lower. Because this is unacceptable in many cases, the uncoated lamps continued to be offered.

In addition there is an aesthetic effect in which the clear lamps deliver light of a much higher colour temperature. This tends to be preferred in countries with warmer weather, or where a stronger contrast is desired with other light sources.

This particular lamp has an antiquated pear-shaped glass envelope, which is much less common than the higher wattage tubular or ellipsoidal types. It employs the A23½ shape bulb which has the same dimensions and light centre length as a standard 200W medium-based incandescent lamp. This facilitated the uptake of low power mercury lamps in standard incandescent fixtures.
Manufacturer: General Electric U.S.A.
Lamp Power: 100 Watts
Lamp Current: 1.0 Amps
Lamp Voltage: 115 Volts
Cap Type: E26s/25 Brass + vitrite
Bulb Finish: Clear Lead borosilicate hard glass
Bulb Type: A-75 A-23½ in eighths/inch
Overall Length: 138 mm 5 7/16 inches
Light Centre Length: 89 mm 3 1/2 inches
Arc Length:
Electrodes: Backwound tungsten Trimetallic oxide emitter
Atmosphere: Inner: Hg | Ar (8 atm) Outer: Nitrogen
Luminous Flux: 3,700 lm @ 100 hrs 3,000 lm @ 9,000 hrs
Luminous Efficacy: 37.0 lm/W @ 100 hrs 30.0 lm/W @ 9,000 hrs
Colour Temperature & CRI: CCT: 5700K CRI: Ra 15
Chromaticity Co-ordinates: CCx: 0.315 CCy: 0.380
Burning Position: Vertical cap up
Rated Lifetime: 18,000 hours Rated to 50% survival
Warm-up & Re-strike Time: 4 minutes 5 minutes
Factory: Ravenna, OH U.S.A.
Date of Manufacture: August 1979 Date Code: 92
Original & Present Value: Unknown
 
References: 1) GE Lamp Catalogue, USA, 1979, p.69