How many tubes? How close? How long for the "on cycle"? These are all factors. I feel t5's will do just fine (as will t8's) with cats as long as:
1) the plants are close enough to the tubes
2) the tubes are "on" for at least 12 hours.
Remember that lighting is accumulative. In nature really bright light (like sunlight) lasts for only a short part of the day length. The parts of the day (the "shoulder" light time) is typically dimmer. The average may be only 2000 FCs in a typical situation. Thus if you can provide 2000 FCs for 12 hours or longer, then that should be similar to the average of the ups and downs of natural lighting. You should be measuring light at the leaf surface, not the tubes.
Let me just add (thus the edit) that you can figure for yourself what you need to provide by selecting a relatively bright spot outdoors and taking light meter readings starting at sunup and going every hour till sundown. Average these readings with the length of the "day" for the season you took the readings (usually summer). This will give you a baseline to use to compare your light readings under whatever lights you use.
You'll find (probably) that even a clear-blue sky day in June will probably average around 2000 foot candles in the northern hemisphere (around 45 degrees latitude). You'll also see that you can use weaker bulbs like t8 as long as they are closer to the leaves. You'll also see that HPS or MH "hot bulbs" will require leaves to be further from the light source for the same FCs.
Hope this helps.
Last edited by Ross; 12-30-2008 at 02:55 PM..
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