Thorn SON-R Reflector Style
The concept of a reflector version of the SON lamp was originally introduced by Osram-GEC in 1976, which offered its 250W, 310W and 400W arc tubes housed within a large reflector-shape outer jacket.  The design was essentially a straight copy of the similar large mercury lamps intended for industrial floodlighting.  GE Lighting in the USA then followed suit with a small 70W product, but still encased in a rather large hard glass envelope, and the lamp was marketed for exterior illumination.

Thorn Lighting instead attacked the commercial interior market with this very compact 70 watt product, among the smallest high pressure sodium lamps with built-in reflector made to date.  Its only serious competitor on size was a proposed R-63 "White SON" lamp from Philips, which never made it into the market.  Because of the axially mounted arc tube within an aluminised bulb, a remarkably tight beam with excellent optical control is produced (earlier large designs only used a diffuse reflective coating instead of the aluminium mirror, and consequently had a rather wide beam) .

The SON-R lamp has never accounted for large production volumes, but found a niche in many interior locations which demand high lighting levels, but where colour rendering is not of paramount importance and low operating costs are crucial.  In particular it finds a home in ceiling downlighters in such places as corridors or wherever all-night interior security lighting is called for.  Today it has been largely eliminated by compact fluorescent lamps in recessed downlighters, which can provide very nearly the same light intensity at high efficacy, but with a white light which is much more desirable in such circumstances.
Manufacturer: Thorn Lighting Ltd.
Lamp Power: 70 Watts
Lamp Current: 0.98 Amps
Lamp Voltage: 90 Volts
Cap Type: E27s/27 Ni plated brass + vitrite
Bulb Finish: Frosted + Aluminised Soda-lime glass
Bulb Type: R-95 R-30 in eighths/inch
Overall Length: 144 mm 5 5/8 inches
Light Centre Length: N/A
Arc Length:
Electrodes: Backwound thoriated Barium Calcium Tungstate
Atmosphere: Na,Hg | Xe Outer: Hard Vacuum
Peak Intensity: 8,400 cd at 1 metre
Beam Distribution: 18° to half peak 70° to 1/10 peak
Colour Temperature & CRI: CCT: 1900K CRI: Ra 25
Chromaticity Co-ordinates: CCx: 0.542 CCy: 0.415
Burning Position: Universal
Rated Lifetime: 18,000 hours to 50% survival
Warm-up & Re-strike Time: 5 minutes 15 minutes max.
Factory: Leicester England
Date of Manufacture: September 1990 Date Code 09
Original & Present Value: £27.73 (1988) £49.81 (2005)
 
References: 1) Thorn Lighting UK Catalogue, 1987/88.
2) Thorn Lighting UK Price List, 1987.