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I know T12s lose 60% in 6 months.

I have always changed T8s and CFs annually.

Supposedly T5 HO linear can go 2 years but I havent experienced that myself.

The cathode tube decays over time and output diminishes dramatically and the spectral output can even shift.

If the ends of the tube are blackened then it is past time to change them out.
 

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Sounds like a Philips number (865). This would be a 6500K bulb if, indead, they are Philips.
 

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1 watt-second = 1 joule; (1 watt-hour = 3600 joules); 1 newton-meter = 1 joule: therefore 1 watt-second = 1 newton-meter.

You should express the light loss in intensity lost. Lumens is meaningless to plants and is an output value of light in the green area of the spectrum that was designed for the human eye.

 

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If you Google GE Technical Pamphlet TP-105 you can easily find it. It is easy to read but bear in mind that cathode tubes are a bit different for each manufacturer and can also vary for the type of bulb it is in.

Also, you dont necessarily want to go by lumens lost (or lumens alone) as this is a scale designed for the human eye in percieving brightness which falls/peaks in the 500nm area of the spectrum and is basically green light.
 
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