Halogen GU10 Bulbs / Lamps
MR16 is a coded designation in which MR stands for multifaceted reflector, and 16 is the diameter in eighths of an inch across the front face. An MR16 is sixteen eighths, or 2 inches (51 mm) in diameter
These GU10 lamps run off standard 230 Volt AC mains without a transformer
Interesting fact : GU10, refers to the lamp cap fitting format invented by Havells Sylvania in 1997, distinguishable from other MR lamps by the 'U' shaped ceramic base mount with 10mm (pin center to center distance) 2-pin bayonet-style twist lock, and by being mains voltage.