Generally speaking short wave will heat, cure, or dry the product in the shortest amount of time. Medium wave will take slightly longer. Long wave will require the most time to heat, cure, or dry the product. There are factors that come into play that make the above statement incorrect. An example would be when heating white plastic sheet, as in a thermoforming application.
Short wave infrared is color sensitive.
Meaning that black colors will quickly absorb short wave infrared, but white colors will reflect a much larger amount of the energy. Therefore, when heating a white sheet of plastic, the medium wave can actually heat the sheet faster than the short wave emitter. Testing is the only way to truly determine the results. All of the heaters in the market do not output energy at a single wavelength. Many factors will come into play when making the decision on which wavelength emitter is appropriate.