The amount of lumans a bulb emits decreases with age, I once read on overgrow its good practise to replace your bulb once a year with constant use.
Bluefunk Reviewed by Bluefunk on . When to change bulb? I have a 400W HPS bulb which has been used for 3 grows: about 1 month at 18/6 and 2 months at 12/12, per grow. When should I change the bulb? Does the bulb just burn out, or does it give warnings that it is waning? Rating: 5