no, no, the spectrum is not always the same... the lamps designed fro aquarium has different spectrum as you need to take into consideration that algae need normally get more blue than red (blue enters deeper in water than red), and water plants need more red than blue to grow. Then you do not want too much blue, in order to avoid algae growth in your aquarium (for salt water aquarium the story is different: you need more blue than red!) in this link, you can see the spectrum of one of this lamps you buy at the aquarium shop:
http://www.hereinspaziert.de/images/Trocal.JPG (Trocal is similar to grow lux) and also the spectrum used by algae (Algen-Spektralkurve) and the other plants in the aquarium (Aquarienpflanzen)
If you combine 6500K and 3000K (3:1 or 4:1) you can obtain a very good balance of light temp for your plants. If you were using only one single tube, I would say, go to the hydroponic shop and buy a very special tube with the correct light spectrum. However, this lamp will be more expensive, and will not provide enough light for your plants!
So, my recommendation: at least 3 tubes (proportion 2:1 (6500/3000K) - not 3:1 as optimal, but trust me, it worked for me for more than one year without problem!
Another interesting graphic is this one
Einfluß der Schalthäufigkeit auf die Lebensdauer von Leuchtstofflampen there you can see that normal T5 lamps (and tri-band T8), after 200000 hours still produce 90% of the light intensity as when new. This has an impact on when you should change your lamps:
you use your lamps at 12/12 photoperiod. This means that your lamps are working 4380 h per year, which would mean that after 4 years your lamps still are 90% efficient... if you give a range of error and some wastage (turning on and off)... I would say, you could change your lamps after 3 years, and not after 1 year as normally recommeded in the package (hhhmmm.. not sure if you have this recommendation everywhere, but at least I have seen in Switzerland
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