As per Hoppy's formula.

Tank 01: 90 X 45 X 45 cm : High light setup : At present using 21 watt X 5 T5 tubes. I am satisfied with the result.

where a= spacing between LEDs , n= rows of LEDs

a2/n=

560/

129.23

=4.33¬=4.5

So, length of 36", if one row of LEDs used= a=(4.5)1/2=2.12¬=2.5

So one led every 2.5inch

For better spread assume you ll go for 3 rows, then a=(4.5 X3)1/2=3.67¬=4"

So 36"/4"= LEDs per row= 9 LEDs, and in 3 rows= 9 X3 = 27LEDs. For safe side go for 30LEDs

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Tank 02: 90 X 45 X 45 cm : Medium light setup : At present using 36 watt X 2 PLLs. Satisfied with result.

same as above dimensions. You can reduce to 24-26 LEDs.

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Tank 03: 70 X 40 X 40 cm : Very High light setup : Using 36 watt X 2 PLL + 14 watt X 1 T5. Not satisfied with result.

560/

129.23

=4.33¬=4.5

For 1 row, we get a= 2.5

As its smaller 40cm, we ll use 2rows for equal spread, so a=(4.5 X3)1/2=3"

So 30"/3"= 10LEDs per row; so two rows= 10 X2 LEDs.

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Tank 04: 45 X 30 X 30 cm : High light setup : At present using 36 watt X 1 PLL. Not satisfied with result.

560/

103.38=5.41¬=5.5

For one row usage, a= (5.5)1/2=2.32¬=2.5" gap between LEDs

so, 18"/2.5"= 7.2LEDs¬= 7 LEDs

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All these are in assumption with CREE XTE, 400 lumens, 4-4.5W LED. If you use CREE XML you might be using 2-3 LEDs lesser in few of the tanks above.

Also please note there are few approximations made above to nearest 0.5 level for easy calculation.

Tank 1,2,3 will have lights at 30" from substrate, Tank4 will have lights 24" from substrate

As you see the LEDs wattage suggested (which is for all hight light tank) comes to more or less than your fluorescent, thats because everyone's definition of highlight and demanding plants varies. As a point of example in first tank, 105W on a 50gallon is still less than 3W/gallon, but been considered high light.

So hope it gives and idea of your requirement.

All the best !

Edit- added heights