@peachfuzz or anyone who has found a good rule of thumb for the life expectancy of lights-
so I run a 600 wt MH/HPS - I Use T5 on my seedlings they really love this a lot and then when they outgrow my seedling space usually by 4 weeks and praying there is no one in the tent flowering lol I then move them into the tent with the 600 MH going at 18/6 for at least a month or so to fill up the scrog fully then I switch to 12/12 for 4 weeks then HPS to finish the last 4/5 weeks of flower. How long before i need to buy new lights? looks like the MH gets about 4 weeks of 18 on daily and 4 weeks of 12 on daily and the HPS gets 4/6 weeks of 12 on daily- T5s get 4/6 weeks 18 on daily -
So how many runs like this until i replace everything?
yes my early veg is T5 then into my tent they get MH for a while and then the last 4-6 weeks of flower they get HPS - just warmer/different color spectrum to finish the flowers into harvest.
The life expectansy of your lamps are about 25 000 hrs. It’s recommand to change them somewhere in the half of that, so around 12 500 hrs of use. For LED’s it’s twice that. It’s between 26 to 30 months of growing time. . So about 6 rounds
Ya I forgot to mention that your bulbs have a estimated life time that should be on the box that it came in … Which I try to get as much out of them as I can so I tend to use them for about 75% of that estimated time before I replace them… I always write the date on the bulb where it screws into the socket when I start using them so I can’t forget how old they are…
Yes, it’s a great idea and tell you when you bought your lamp , and give you a pretty fair idea when to change it, however it don’t tell you how many hours it have under the hood a 4 month of growt roughly take 1900 hrs , so 6-7 growt will approching the half life expectansy of these lamps… Of course, you probably can push it for 7-8 growt @gpitel
I read about this some place and I believe a lot of it depends on the manufacturer of the bulb some will have a longer life span than others. The recommend lifespan should be labeled on the bulb box or in the description link on whatever website your looking on. And at the halfway point they start loosing lumens and can still be used just with less results. You can also, I’ll just use a 600w ballast cause that’s what I also use, get a higher watt bulb than 600w say a 1000w bulb and it will expand the life span of the 1000w running at a lower wattage.
In theory it can work , is it safe ? I don’t know ! An electrician is more likely to give you a safer respond Maybe @Allen13420 is one and surely have the knowledge by experience, and will respond
Personnaly, I would not try it, i’m kind of fire hazard scared by electrical experiment
It is not ever recommended to use a lamp or ballast that is of different wattage.
Never put a 600 watt lamp into a 1000 watt ballast.
Never put a 1000 watt bulb in a 600 watt ballast.
Using lamp systems incorrectly can cause you to burn out the ballast or the lamp/bulb and cause you added expense. Be very careful when you receive advice that appears to be speculative or read about somewhere!
Happy New year and happy growing to you too @latewood happy you are stepping in and i’m wondering how fast a HID lamp (bulb) is decaying after 365 days of use and how it’s affecting the growth of cannabis, knowing that the half life expectansy of the light as not been reach ?
Yes I am certified in my state and do contract work on residential houses but I am no expert in growing or light fixtures and not here to cause any problems so I’d just listen to the expert here I was giving my two cents worth on the subject.
No need to apologize you have done nothing wrong. I’m just not the arguing type I absolutely hate to argue about anything, I like to just keep the peace, although it does happen! And with most ballasts and bulbs being made for adjustable settings such as the one i have has 3 settings for 100%, 75%, and 50%. So naturally you will be using a 600w bulb at 300w when set at 50%. So how is this different than runnin a 1000w bulb at 600w. As long as the bulb is made for a dimmer adjustment I don’t see any problems. Like I said I am no expert and I will also take the advice of @latewood over something that I read on the Internet someplace. I have the upmost respect for all the guys responsible for this site and forum, as they are experienced and very well knowledgeable about growing. Honestly I’m very glad you started this tread, after this grow I will have roughly a year on my bulbs so it’s time to replace them and I was going to try out the higher wattage bulb but I believe I will just stick to the manufacturer recommend replacement. Also these are things noobies like us need to know and anybody looking for the same answers about the lifespan of their bulbs will hopefully find this thread and it will help them out.
Hey I think the missed point was that you should have an adjustable/dimmer switch ballast for your 600w or 1000w then it will stretch your lifespan of your bulb immensely
It’s between 26 to 30 months of growing time. 
. So about 6 rounds 
your awesome! Thanks for that!
and i’m wondering how fast a HID lamp (bulb) is decaying after 365 days of use and how it’s affecting the growth of cannabis, knowing that the half life expectansy of the light as not been reach ?