What does an 'Ink Low' message mean?

It normally means that your printer and/or its cartridge's logic, estimates that your ink is getting low. Often the calculation is made simply on the basis of the number of pages you've printed, and will not be based on an ability to measure the amount of ink left. Who knows, this may change in the future. However, in most cases you should be able to continue using a cartridge until the print quality simply becomes unacceptable.

Where the 'Ink Low' message is useful, is in advising you that it may be a good idea to have a back-up cartridge close to hand. In fact, we recommend that you always have a spare so that you're not forced into making a panic purchase, which by their nature are normally expensive purchases.

Read the documentation 

In all cases we recommend that you read the manufacturers' documentation in relation to your ink product, and understand exactly what an 'Ink Low' message means for the operation of your printer. And do remember to read between the lines. They will be only too pleased if you were to replace this profit-making consumable prematurely.