Philips SOI/H 45W Darkroom Safelight

During the development of photographic papers in a darkroom, certain wavelenghts to which the paper is not sensitive can be used for general illumination. Ordinary incandescent lamps equipped with narrow-band filter coatings are traditionally employed, and are available in a variety of colours to suit various types of photographic paper. Owing to the low luminous efficacy and the fact that only a few narrow wavelength ranges can be transmitted, the total luminous flux emitted can be extremely low, in many cases less than one lumen. While such lamps may be adequate for the amateur photographer, a greater quantity of light is required in larger commercial darkrooms.

In such situations an ideal source of light is the low pressure sodium lamp, as many types of paper are insensitive to its deep yellow monochromatic light. However the spectrum of these lamps is contaminated by weak blue and green lines, and continuous radiation from the glowing electrodes. While these wavelengths are completely insignificant in general lighting applications, they can cause fogging of photographic papers at high light levels. Darkroom luminaires containing sodium lamps are therefore equipped with additional filters.

Before such specialised luminaires became popular, Philips marketed for a brief period this highly unusual sodium lamp whose outer bulb is painted with an orange filter. The integral filter cuts out almost all wavelenghts other than the sodium resonance lines. The rest of the construction is identical to a standard 45W SOI/H type lamp. No reference to this lamp has been found - perhaps it was only marketed for a brief period of time until luminaires with integral filters were developed around standard sodium lamps.
Manufacturer: NV Philips Gloeilampenfabrieken
Lamp Power: 45 Watts
Lamp Current: 0.6 Amps 0.54A starting current
Lamp Voltage: 80 Volts
Cap Type: By22d Porcelain insulator
Bulb Type: T-50 T-16 in eighths/inch
Bulb Finish: Clear Soda-lime
Electrodes: CCC-4 Black Tungsten BCT emitter
Arc Length:
Atmosphere: Na | 98.5% Ne, 1.5% Ar Outer: Hard vacuum
Luminous Flux:
Luminous Efficacy:
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: 6000 hours
Warm-up & Re-strike time: 7 minutes Instantaneous
Burning Position: Vertical Base Up ± 95°
Overall Length:257mm 101/8 inches
Light Centre Length:160mm 61/4 inches
Factory: Eindhoven The Netherlands
Date of Manufacture:
Original / Present Value: Not Known
References: 1) Fluorescent Lighting Manual, Charles L. Amick, General Electric Company, March 1942.