What is the difference between heat lamps and infrared space heaters?
The exact space heater in question would effect answer, generally both use invisible light to heat surfaces rather than heating the air. What varies is how much of the IR is reflected and how much is absorbed by the fixture or lamp then locally projected by the device.
Electrical heat is not very efficient, any watt produces the same heat no matter how dispersed, 3412 btu's per kw/hr.