OK.
First, there are three different types of fixtures out there. The bulbs are all different and are not interchangeable between fixtures. The most "common" is the "Standard" bulb that you can find in any workshop fixture at Home Depot of Loews. These are available in "Growlight" spectrums too, but they have the least light output as measured in Foot-Candles.
The next are the T8's. These have better output over the standard bulbs, but are no where near the output of the T-5's.
The T-5's have the greatest output (again measured in Foot-Candles) of any flourescent bulb currently available on the market. They are very slender bulbs as compared to the standard or T-8's which is said to be one of the reasons they are so efficient at producing stronger light.
One can typically get the Standard and even the T-8's at places like HD, Walmart and Loews, but they typically don't carry the T-5's.
One place to look is
cPanelŽ. I have gotten several fixtures there and they ship rapidly and securely. They have good prices and DO include the bulbs with the cost of the fixtures which others may not. They are NOT cheap, however, so be prepared to spend over $500 for an 8 bulb, 4 foot fixture.
The "goal" of Foot-Candle (FC) lighting is really dependent on the particular plant, even within the species. Some can grow and bloom in less light than others. In "nature", Catts are said to get over 2000 FC's of light, tolerating 3000 to 4000 if the light is not direct. This is where the interpretation of light comes into play. The crux of the argument is that light via artificial means is CONSTANT and natural light is not. Therefore, if plants are supplied constant light at even 1500, 2000 or more FC for a 14 hour day, they may actually - at the end of the day - have more light received than if they were in "nature".
The other issue is that of heat on the plant's leaves. That is why direct sunlight can burn a plant so easily. The flourescent lights produce less heat (read "less" not "none") and can be placed closer to the plants to achieve the desired FC level, provided that air circulation is still maintained.
I typically have my light meter out and measure the FC ratings at the top leaves and at the bottom leaves of the plants and adjust the lights to achieve a balance - typically about 2000 FC.
Then I watch the leaves - they will typically tell you what they want. If they lighten to a light green, they are happy with the light that they are getting. If they are still very dark green, they are asking for more light. If they start looking sunburned (which I managed to do beginning the T5 experience), then they are getting too much light.
I have found that the light readings are dependent upon the size of the fixture that I am using: that is, more light is generated at the center of a 4 foot 8 bulb fixture than at the center of a 4 foot 2 bulb or 2 foot 8 bulb fixture.
Air movement is important the closer you get the plants to the light source as the heat increases the closer one gets to the light.
Now, you could also consider changing to MH lights, but that is another topic in itself!!
Hope that his helps you.
switch from regular plant fluoros to T5?
) but I also have my "high light species" in a south window with t5 lights as supplemental lights, not primary. I recently installed an 8 tube fixture and measure 3600 foot candles. Now that's pretty strong!
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