The WPG formula looses it's effectiveness when dealing/w a tall tank.
What type of CFL bulb are you using that cost MORE than an LED set up ?
Can you give a link to a picture of them ?
Measuring from the top of the sub to the bottom of the bulb, tanks/w more than about 15" will need either more bulbs or higher Watts. The 13W and even the 9W ones are good(1 of them) for a 12" tall tank such as a 10g or 2 for a 20L tank.
Option 1:
I understand that for CFL I could use the screw in type with a U shape, and possibly use 2 for my tank, but I would like to avoid CFL - due to heat output and annual replacement. This will probably cost me around $60-$80 where I live.
Option 2:
Pre-made LED solutions for aquatic plants are very expensive. This will cost me around $200-$250 for a high end solution, and maybe $60 for a clip-on, but that would require the removal of my hood and hard to find the correct spectrum they are usually 10000K.
Option 3:
My planned DIY LED is currently costing me $30, plus some soldering and glue-gun work. Of course I'll have to monitor the effectiveness of this system.
Of course I'll have to adjust my plans as I test different things, I'll start with a 6 hour photo-period and slowly move up to determine what's best for my environment.