The truth is that nobody really knows. Most figures that you will see will show you a number where the diode will still produce light, but nobody really knows how long they are effective. A T5 or MH bulb can light for 10 years too, but they are probably not valuable to a reef after two years, or so. Nobody has really measured the output to look for shifts in spectrum (good or bad) with regard to nourishing corals - no real science. All that you are going to get here are anecdotes.
They anecdotes can probably give you all that you need. There are people still using 5-8 year old panels to some degree... so it seems reasonable to think that 10 years is not out of the question. More reasonable, four or five years is what most people do just because they feel the need to "upgrade" for either different diodes, better software and connectivity or just for cool ness. If you are using a panel for more than 5 years, then you will be in the minority, but not alone. Once true UV and IR get more and more common in panels, then people will probably upgrade again. Adding T5s have extended the usability of nearly all panels with something like a AquaticLife Hybrid unit filling in a lot of gaps and making up for any shortcomings of an older panel.
