Here I disassembled the broken fuser assembly from Xerox DocuPrint N17 printer and pulled halogen infrared light bulb out of it. The fuser assembly simply used the infrared light bulb to heat the fine plastic pellet toner to fuse into the paper.
I saw several of these infrared halogen lamps (When operating) inside analog and several digital copiers and an old laser printer and a laser facsimile from Sharp.
Today most of the laser printers, don't have these lamps as the heating element for their fuser, as their warming up time is very short, and with the HP Laserjets, their warming up time is totally eliminated (The current Laserjets begin to print the document as soon as they recive it, regardless if their fuser is hot or cold, as their fusers reach theirs operating temperature within 0 secs, what that called "instant on fuser". Indeed the fuser of the Laserjets even turns off 5 secs after finishing the printing [The clicking noise that heared from Laserjets few seconds after the printing was finished]).
@dor123: Which HP LaserJet model does it has modern heating element? If I come across with defective fuser assembly with new heating element, I would be sure want to take it apart
The new ones use a ceramic bar with a thick film heater resistor screened across one side of the bar. It has a glass frit seal, and is in direct contact with the inside of the fuser roller, the paper running on the outside of the roller on the PTFE impregnated side. These have a temperature sensor inside the sleeve contacting the back side of the ceramic, as well as a thermal switch on the ceramic carrier. The actual sensing is done by a small NTC thermistor in a Kapton sleeve on the other side of the assembly, measuring the temperature of the element both during run up and the paper during fusing. Both sensors are used by the microcontroller inside the printer to control temperature. Bad is that the fuser assemblies are both fiendishly expensive, model specific and prone to early failure. The lamps last essentially forever, as they have a warm up cycle and drop to a low duty cycle in inactive periods to save energy, and never have sudden thermal shock.
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Today most of the laser printers, don't have these lamps as the heating element for their fuser, as their warming up time is very short, and with the HP Laserjets, their warming up time is totally eliminated (The current Laserjets begin to print the document as soon as they recive it, regardless if their fuser is hot or cold, as their fusers reach theirs operating temperature within 0 secs, what that called "instant on fuser". Indeed the fuser of the Laserjets even turns off 5 secs after finishing the printing [The clicking noise that heared from Laserjets few seconds after the printing was finished]).