Solar powered LED via capacitor?
My reseach so far indicates that a 6v 1F cap can light 12ohm LED for
  approx 8 hours, but I need far more understanding to know if this
  calculation is correct


6 volts and 1 farad is an energy storage of 18 joules (\$C\cdot V^2/2\$). Spread over 8 hours that's a power of 18/(3600 x 8) watts. So, if you consumed a power of 625 micro watts from your capacitor you would take an energy of 625 micro joules every second and over an hour that would be 2.25 joules and over 8 hours that would be 18 joules.

You also need to consider that only about 75% of that energy is usable because as the capacitor voltage droops below 3 volts your LED driver circuit may falter and switch off the LED.

It's nowhere near enough for even a standard red LED at 1 mA and 2.0 volts.


  Any help would be great?


Glad to oblige but I would recommend dismantling one of those garden lights to see what they use then scale up your PV panel and battery/supercap accordingly to match your needs.