Lamp Lumen Loss Over Time

i just recieved a digital light meter model lx 1330b( 200 k lumen max) that i bought on ebay for 25 euro incl shipping

ill find some place to make accurate and a like readings
than i have a shit load of 400 watt bulbs i can measure and do comparisons with

reflectors currently:
Open standard model ( eurowing/dutch barn)
and some phillip gh lamps with built in hood
later ill buy a batwing also when i get more money

bulbs:
a osram planta star - used for a few months
ge localox hps - brand new
osram mh -brand new
20 x phillips son t pia - used for unknown length of time ( came with used gh lamps)

i also have 250 watt both metal halide and hps and a 125 watt cfl to compare with also

heres the charts for 400W Lucalox XO ( extra output)
Output: 56.500 Lumen!
Farbtemperatur: 2.100K
Brenndauer: 28.500 Stunden






heres the charts for 600W Lucalox HO ( high output)
Output: 86.000 Lumen!
Farbtemperatur: 2.000K
Brenndauer: 24.000 Stunden



from this it seems theres even a large difference in lumen output loss over time for models in the same brand
if we use 10% lumen loss for a guideline on when to replace bulbs we see that
XO lasts 21000 hours but the
HO only lasts 14000 hours

but still a lot longer than what ive heard so far about replacing bulbs for every 2 grows ( 2 x 8-9 weeks on 12/12)

replace your bulbs every 2-3 grows max

i have tested many times over and find a new bulb will net you 10-20% more then a year old bulb

i ran same strain for 5 years whith exact same nutes and soil in exact same room whith only thing ever changing was bulbs

after about 2 years or so my pulls were down 25-40% and could not for the life of me figure out wtf was going on
i mean i knew i was getting better at growing but my buds were half the size of my first grow

i then discovered the internet and overgrow change my bulbs for first time after some reading and total harvest jump 40% from previous grow under same conditions

I run 3 1K horties in an 8 by 8 and have replaced my lamps since I last posted.I did probably 5 grows on my last trio of lamps and changing them visibly made the room much brighter.I dont need a meter to tell I wont go over 4 grows again