My new refrigerator has the water filer, and a series of lights to tell me when to change it. Green, Yellow, and Red for OK, replace soon, and replace now!!

My question is how are the lights activated? Is it a simple timer, or a meter that monitors the gallons filtered?

The light has turned red--second time in a year. These filters are not cheap. I see no loss of flow from the dispenser; the stream is as strong as ever.
Will anything be damaged if I ignore the light until I see some reduction in flow?

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags