This is a General Electric R40 Reflector Flood Lamp - 300 Watts/120 Volts. Its rear is coated with an opaque reflective substance that helps direct and intensify the beam projected forward from the bulb. It has a medium E26 Edison screw base. It has a front diameter of 5" (12.7cm).
For a clear, "Spot" version of this bulb, Click Here.