Circline Twin-tube FHD40EL
Although the Circline fluorescent lamp was invented in America and also quickly further developed by the European manufacturers, it never became an especially popular light source in either of those countries. Meanwhile however, it was embraced with unparalleled popularity in what might well be referred to as its adopted home country - Japan. This unusual twin-tube lamp is typical of that country's pursuit of excellence in refining the concept for optimum performance.

Owing to the high population density, space is expensive in Japan and product dimensions are important. It is atherefore a great advantage if products can be miniaturised, and this lamp has been made to satisfy that goal.

Circline lamps are popular for the general illumination of living spaces, and a high luminous flux, typically also of of high colour temperature, is required to compensate for the relatively low sensitivity of the Japanese dark eye. This has traditionally called for circline lamps of large diameters - even stacked configurations of a small lamp within a larger outer ring. Matushita was the first to present a solution to this problem with its twin-tube lamps, which deliver increased luminous flux for a smaller lamp diameter by fusing two concentric tubes into a single lamp.

Tube diameter has been reduced to 20mm for optimum efficacy, with both electrodes being side by side at one end of the ring. At the opposite end the two tubes are joined by a small glass bridge. A dead space is left beyond the bridge, this being cooled with the aid of ventilation holes in one side of the cap, to help keep mercury vapour pressure low enough for optimum efficacy at an ambient temperature of 40°C.
Manufacturer: Matsushita Electric Works
Lamp Power: 41.0 Watts
Lamp Current: 0.43 Amps
Lamp Voltage:
Cap Type: GU10q
Bulb Type: 2T-20C 2T-6.3C in eighths/inch
Bulb Finish: Triphosphor Deluxe Lead-alkali glass
Electrodes: Triple Coil Tungsten BaCaSrCO3 emitter
Arc Length:
Atmosphere: Hg | Ar
Luminous Flux: 3,020 lm (@ 100h, 25°C) 3,200 lm (@ 100h, 40°C)
Luminous Efficacy: 73.7 lm/W (@ 100h, 25°C) 78.0 lm/W (@ 100h, 40°C)
Colour Temperature & CRI: CCT: 3000K CRI: Ra 84
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: 20,000 hours
Warm-up & Re-strike time: 1 minute Instant
Burning Position: Universal
Dimensions: OD: 192 mm, ID: 106 mm OD: 71/2, ID: 43/16 inches
Mass: 186g
Factory: Okayama Japan
Date of Manufacture: March 2003 Date Code: 3C18
Original / Present Value: JP ¥1980 (2004) approx. GB £14 (2015)
 
References: 1) Panasonic Lamp Catalogue, 2015.