I finally got around to buying replacement T5 lamps that are 20 months old. I’m replacing one lamp a week after doing a 50 hour burn in on the new ones to avoid any sudden spikes in lighting. I was curious about the difference in light output so I pulled out to old lux meter.
Not a hugely scientific study, but something to record. I’m placing the meter dead center and about 6 inches in from the front glass since it is an easy spot to reproduce using my lid and I’m measuring at 11A each day
Start: The old lamps put off 19,170 lux.
Lamp 1: Blue Plus, now at 20,200 lux. (~5.4% increase)
Lamp 2: Blue Plus, now at 20,800 lux (~8.5% increase)
Lamp 3: Coral Plus, now at 25,900 (~35.1% increase)
Lamp 4: Purple Plus, now at 26,000 (35% increase)
I’ll update again in a week when I put the next new lamp on.
EDIT: I’m expecting more of a change when I swap in the new Coral Plus bulb since the blues seem to hold their spectrum and output well, but the fuller spectrum ones don’t and this one is almost double the recommended replacement age.
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Interesting, I thought there would have been a larger drop for a 20 month old bulb. You do a better job than what I do. I replace all 4 T5 's (2 Actinic/Blues and 2 Super Actinic) at once. I raise the fixture 1.5 feet and then lower it a little at a time.
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I think so long as you do something to address the jump in par, you’re good. I’m going to swap a second new bulb tomorrow. Another blue plus, so not expecting a huge lux bump, but we shall see…
Added the second Blue Plus. Only a minor change in lux, now at 20,800, but that’s 8.5% more than where I started. That’s not surprising since that lamp is on the other side of the tank. Next up is the coral plus. Based on what I’ve seen in tests on those lamps, they lose output quite quickly. I think there’s going to be a big bump with that one next week.
Happy new bulb Tuesday! I swapped out the Coral Plus bulb today and HOLY COW! Lux jumped up to 25,900! That brings us a whopping 35% higher than the old bulbs now. Still one more Purple Plus to add next week.
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Very interesting!! I like the weekly updates!!
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Wow - that’s significant. Good thing you are changing them one at a time…
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Just added the 4th and final bulb. Didn’t make a huge difference, but the lamp is on the other side from where I’m measuring. Ultimately, the 4 bulbs led to a >35% increase in lux. Corals all seem happy with the change. I guess I better keep up with the swaps in the future 
