A typical lamp and its circuit is shown in Figure 22.8. The basic lamp type is coded as SON (SO = Sodium vapour, N = high pressure), but two other variants are labelled as SON-T (a tubular clear glass type) and SON-TD (a tubular double-ended clear quartz type). The illumination by the SON lamp is wide-spread and delivers a golden-white light.
Lamp starting is achieved with the help of a high-voltage pulse from an igniter circuit, which ceases to function once the main arc has been struck. At least 5 minutes are required for the lamp to achieve its maximum intensity and will usually re-strike within 1 minute of extinction from a hot condition. SON lamp power ratings range between 70 and 1000W with corresponding luminous efficiencies being between 80 and 120 lm/W.
