At least 2-3" ...
As distance increases , your available lumen output drops.
More Light = More Bud ********
CFL Pros :
Low startup
Available everywhere.
Spectrums from 2700 up to 6800 Kelvin
Low cost power
Scalable
Cons :
Poor penetration below a foot ( spiral CFL )
Poor choice for larger grows
But ........ For the SMALLER GROWER ( 1-2 plants ) and AutoFlowers its a great way to grow. These work best for plants under 4 foot.
For early seedlings : keep close ( couple of inches ) 5000k OR HIGHER -
DAYLIGHT BULBS. These have a whiter light with a shift into blue spectrum.
Use at least 100w of CFL to START PLANT. You can split this into TWO BULBS.
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Here im using 2 100w ECOSMART ( home depot ) bulbs DAYLIGHT 5000 Kelvin
Example : 2 ( 60 watt ) or 2 ( 40 watt ) .
You will need at LEAST 2000 lumens or better to start plant growth.
PER PLANT !
Even at this level ... Your plants will be weak. This is why the more the better.
You want between 7000 to 10000 lumen. Roughly 4 - 5 bulbs per plant.
You can INCREASE penetration with added side lighting for lower plant areas.
As plant continues to grow : INCREASE NUMBER OF BULBS
Use a MIXED SPECTRUM ( kelvin ) for better results.
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View attachment 3704172 This bulb cost 59¢ PER BULB !!!!!!!!
I bought a shitload of these.
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