how do you know when your lights stop growing

a friend of mine was telling me that after a certain amount of grows your light bulb lozzes the lumins it takes to grow your plants. has any one had any experience with this and if so what are the signs and signals to tell if the bulb should be replaced. my plants are not growing very fast and i was wondering if i should buy a new bulb. im thinking of getting a gold halide. i have no idea how long ive been running my light so i can not tell if i need a new one. any input would be great.

I posted the same question in a new thread yesterday and only got NEWBIE gueses. I was asking about CFLs or flouros.
I did read that just like tanning bulbs, after a while, they put out LIGHT, to our eyes, but they put out less lumens with use.
I too want to know how many grows can I get from my bulbs before I need to toss them and buy new ones.
I'd like to see documentation of facts about this.

12 months is the recommend usage for MOST hid bulbs. i think it was recommended to only do like 3 grows per bulb. if you look at the box ur bulb came in, it will tell you. or look it up online. its different for each bulb, but like i said, average is 12 months.

According to "www.4hydorponics.com" Metal halide bulbs lose 15% of their life after 12 months of 18/6. They also claim HPS bulb have a longer life expectancy of around 2 years, though no specifics are given as to percentages or daily hours of use. Another site lists LED's as having anywhere from 20,000 to 100,000 hours of useful life according to manufactureres specs, which they claim is 10-50x longer than traditional grow bulbs (not sure how much I believe that one...), and another sites lists the LED product life as 11.41 years if running 24/7 (and only using 6 or 9 watts too).

I have some cfl bulbs in the flower room that have been there for 6 years. Up against some new ones that I bought this year you can see some difference but, very little. I'm using my old ones for sidelighting.

Fluoro tubes dim significantly after about 2 years in the growroom. I know that because I've been using them for 20 years. But, they make great sidelights because your plants can lay right up against them.

yea i wold agree that old bulbs would make good side lights. a year sounds about right. im sure new bulbs will produce alot better lumins and i bought the cheap bulb so if i got an expensive bulb i bet it would grow alot better plants all the way around. has any one compared cheap bulbs to the agro suns and shit. i think i just need a good grow bulb.

just added a 105 watt cfl 6500k. its really brigh,t hanging vertical, soket assembally was only 15 dollers. the bulb was 60. i like it .

While replacing your bulbs every year is a good idea, its not like they just die after 12 months of use.
The MH in my veg room has been in operation in various grows for about 4 years. and despite the fact that i often have waay too many plants under it, it still grows plants just fine.