T8 tubes in T12 fixture, overdrive fluorescent

We have a plant grow fixture made for two T12 48 inches fluorescent tubes with an electromagnetic old fashion ballast. This ballast is made to push 40 watts per tubes.

From my indoor growing experience, the light output (lux measured at 1ft from tubes on a white sheet of paper) was looking quite low with the two original T12 tubes this fixture was coming with.

I measured the light output from the two old tubes, my reading made with LightMeter iPhone app (maybe not scientific but fair enough for my experiences) was of 2500 lux.

After I had a hand on some two used but good T8 tubes from Philips and installed them in the fixture and waited 3-4 minutes for full warm-up, the measured value following the same protocol was of 16000 lux.

Just as a comparaison, we also have the same T12 fixture but 24 inches long in which we put brand new T12 grow tubes last year and this one has been measured at 8000 lux.

Returning back at our T8, these tubes are made to run on 32 watts and now get 40. Also, they are made to be used with an electronic start ballast so they had some flashing / flicker state during 2-3 minutes when I first cold started them. They were just out from the garage at -5degre celcius so maybe next time, the warmup will be a little quicker.

Affer 3-4 minutes, there was no more flickering, the light was perfectly solid and quite bright to start plants indoor.

Math made, bulbs are actually running at exactly 125% of thier designed power. How long will they last with a 25% power increase, I would believe at least 50% shorter… but only time will tell. These used tubes were found free in the garbage close to a renovation field so, for free tubes, if they last 3-4 month for us to have the time to start our seeds inside during this spring, that will be awesome.

Note that I will add a low velocity fan around the tubes just to move some little air in order to cool them and the ballast as well.

I’ll post an update when time will be arrived to transplant young plants outside to tell you how the overdriven fluorescent tubes went on the long run.

Here are some pics of the thing…

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