What's the difference between R63 and R64 light fittings and lamps? I presume the numeric bit in R50, R63, R64 and R80 is a nominal diameter in millimetres: does this mean R63 and R64 are just a mill different? Are they in practice interchangeable?
Yes, with Rx reflector bulbs, in Europe, the x represents the maximum diameter in mm.
(Whereas in North America, the x represents the maximum diameter in eighths of an inch).
With PARx bulbs, the x represents the maximum diameter in eighths of an inch in both Europe and America. So PAR38 = 38 x 8 x 25.4 = 121mm diameter.
A quick bit of Googling shows that Osram, GE Lighting, and Philips offer R63, but Crompton offers R64. This is why the designation R63 is more common. They are interchangeable (but bear in mind that you can get ES cap and SES cap in the smaller diameters)
Yup
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