It is not fun to go and print something out only to notice that it didn't print out right. One of these problems is when light prints on the side of the paper. There are usually two scenarios where this can happen and it usually depends on what kind of toner cartridge the printer uses. If your printer's toner cartridge uses both the drum and the toner in a single unit, like many HP toner cartridges, then the problem is most likely caused by the cartridge itself.
When the cartridge is the likely cause of the problem, it is probably because the toner is not in its slot correctly. Light is then printed onto the paper because one side of the cartridge is installed correctly into the slot while the other side is not. It might be too far away from the paper while the printer is printing and this is how the light is printed on that side.
The best way to test for this problem is by powering down the printer. Remove the power cord from the wall or the printer as well. Next, open up the access panel of the printer. This will either be on the front or the top of the printer to expose the cartridges. Remove the cartridges and then reinsert them correctly according to the manufacturer's instructions. Once you have reinstalled, turn the power back on and see if this fixed the problem by printing a test page.
Another problem that causes light prints on the side of the paper is the drum itself. If your printer uses a separate imaging drum from the toner, then the drum is most likely the cause. In these types of printers, the laser toner is first transferred from the cartridge to the drum. Then the toner is transferred to the page that is printing. If the drum is dirty, oily or scratched, this could be the cause for light printing on the side of your paper. If the cause is your drum, it is best to replace it or have it cleaned by a professional. It is a sensitive part of your printer and it is not recommended to try and clean it yourself. Doing so can result in breaking it or causing damage to your printer.