That depends mostly on how you run your lights and maintenance. ex: If you run the lights 4" from the water at 100% power for 12 hours in a canopy with no ventilation and do no cleaning/maintenance, they probably lost a significant amount of power. If you ran them at 8" above a tank with no canopy and minimal water splashing, plus ran them at our suggested settings, say around 70% power max, then after 6, nearly 7 years, I would say about 25% power loss- so you can turn the light up to compensate.
Let's be reasonable here- this isn't a car. At 5-7 years, you probably want to consider a new light. While there are plenty of V1s still going, at this point I would recommend updating to the new V2+. It's a huge leap in terms of control, color, efficiency, form factor, mounting options, and much much more.
Think about it this way. The average person gets a new $500-$1000 smartphone every 2-4 years- while I know this isn't an exact comparison, a consumer product lasting well over twice that period is considered very reliable. For example- if you had the same phone you did in the start of 2014- it'd be the iPhone 5s. Would you expect that phone to make it until 2020 with no cracks, dents, battery lifespan loss, all buttons working etc.? Do you run that device 12 hours a day, 24/7, 365?
That being said, if you want to hang on a little longer, we do have app enabled hardware coming in 2021 (all current V2/V2+ can easily be upgraded to run the app after release). And- new lights have a 2 year warranty. We're very confident in the quality of our lights. And if your first light you got from us lasted 7+ years- why not get a ReefBreeders when it's time to upgrade?