The average power of sunlight ground level at the equator about 750 watts/SqM is seem to remember although I have read numbers from 1350 as the number that hits the outer atmosphere too. Not absolutely sure here.
So that would be your maximum illumination. Obvipously the watts need to be conberted to lumens an I have no idea how to do this for sunlight.
Now it depends which plants you wish to grow as some plants need more red (IR) whilst some grow better in sunlight containing more blue (towards UV).
LEDS are tailored to put out light at specific wavelengths and their output drops of very fast outside this. An incandescent (filament) light bulb give out lots of IR (they're hot, right?) whilst fourescent tubes (sometimes inaccurately called neon tubes in some countries) put put more blue light.
I think that I would decide what I wishe to grow and then try to get a look at a pic of a professional grower environment of the same plant and see which lights they use. Once you have this, find out the wavelength of these lights and then find LED(s) that conform to the same output frequencies.
I am sorry not to be more specific but there really are a lot of variables in here.
My daughter-in-law grows some plants in her kitchen under a brace of white LEDs and they do alright.