The Osram EKE is a 21 volt (21V) 150 watt (150W) halogen Microscopy Lamp with a focusing MR16 dichroic coated reflector.  The ANSI standard lamp has a 200 hour rated life.  The Osram EKE is also known as their part number 51494 and EKE-21V-150W.  Equivalent lamps are also available in excellent quality from GE, Ushio, Philips, Hi-Tech Lamps, Britelite and Phoenix Electric, while many low quality sources are also available.  
PRICE: $6.49