Most of the work is done on a light sensitive Photoreceptor drum in small laser printers. At some point the surface of the drum is removed of charge, then the laser sweeps across it charging it, then toner is electrostatically attracted to the charged parts of the drum, then the paper touched the drum and the toner electrostatically transferred to the paper, then the drum is cleaned up and all charges removed, and the whole cycle starts all over again. Selenium used to be the photosensitive material of choice.

The LED's are probably used to clean the drum.

The paper and toner then goes through the heated fuser roll which uses heat and pressure to melt the plastic onto the paper.

The sensor may be a paper edge sensor, the printer has to know where the paper is for good registration.

$product is similar, but bigger and more complex. It has four laser assemblies (for four colors of toner, each toner tank is almost the size of a scuba tank), a 15 inch by 72 inch (roughly) organic flexible photoreceptor belt, air conditioning and a 400 pound fusing assembly.