H100 High Pressure Mercury Discharge
In North America and Japan, it is interesting that a significant market has remained for clear mercury discharge lamps after the introduction of the improved type with fluorescent outer bulb.  At the time of the introduction of the coated lamp this was understandable because they were considerably more expensive than their uncoated predecessors.  However, this particular lamp was made in 1995 and for many years leading up to this both lamps had been offered at the same price.  In fact today being something of a rarity, uncoated lamps command a significantly higher price than the superior fluorescent lamps!

The higher wattage types are made in clear tubular bulbs while the lower wattage versions are offered in both the ellipsoidal, and this antiquated pear-shaped glass which has the same light centre length as original lamps.  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 which is the main reason for their continued use in Japan.  The clear lamps deliver light of a much higher colour temperature and this tends to be preferred in countries with warmer weather, or where a stronger contrast is desired with other light sources.
Manufacturer: GE Lighting
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: 90 mm 3 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: December 1995 Date Code: 92
Original & Present Value: Unknown