This is a great subject. Forget LED's. Wimpy. The plants care about lumens, your wallet cares about watts.
The sun has approximately 1KW per square meter. LED's aren't going to work. So here are some suggestions because we were constrained by budget and this is what we've done
Get an 8 bulb (T-5) fixture that takes very little power. No ballast is needed It will put out 40,000 lumens at 500 watts. This is the lowest cheapest system we found to use and used successfully to grow vegies from seed to harvest. Cost; $250 and came with 8 bulbs in the blue spectrum. We purchased 8 bulbs later to get the red spectrum and reproductive growth going; cost about a hundred bucks...that you don't have to spend until you get your plants through their vegetative stage, no matter what kind of plant. The red spectrum triggers reproductive growth for tomatoes the blue would be fine for leafy greens the entire time.
We finally were able to afford a grow light fixture with ballast , comes with 2 bulbs, a metal halide bulb which is in the blue spectrum and a second bulb, high pressure sodium (hps) that functions in the red spectrum. One bulb at a time depending on your project, we've had ours for 2 years full time use and still fine. 2 bulbs, the fixture the ballast for $250 to $350. We got ours on some special deal at $250. This provides LUMENS 80K for metal halide and 95K for the high pressure sodium.
Look up HTG Supply for lighting, we got our best deals through this company.
One other answer that would follow your idea of a grid would be to use CFL's Compact Fluorescent Light in place of your LEDs. (Those spiraled light fixtures we use now in place of the incandescent bulbs). The one problem you will have with those is the fixture or lack thereof. The light goes everywhere not just the plants so a lot of energy and light is wasted. LED's, we TRIED using them and just not enough light period. Turned out to be a joke.
You'd need 6 CFL bulbs 300 watt full spectrum spaced each meter, paint the walls white and somehow devise a reflector for the bulbs. Each bulb costs $30 to $50 bucks each X 6 = $180-$300, not including your fixtures, the wiring, the need for a dedicated breaker in your electrical panel, the paint and I kid you not the fans you have to have. A way to get fresh air into your system, dirty air (full of O2) out of the system and a heater! Timers, drainage? Fans to move the air forcefully not used for cooling to prevent the higher humidity promoting fungus. You'll end up eventually purchasing a humidifier. The best fertilizer you can afford and understand or go Osmocote for safety and expense. Soil, potting soil, sterilized soil isn't expensive but if you don't use potting soil I wouldn't bother getting lights. Drainage for your pots, properly sterilized pots with holes, sized for the plants. You never put a tiny little plant or start in a big pot. You have to up pot at least 3 or 4 times using potting soil. So the expense in tiny pots 2-3" max for growing from seed to 4 and 6" pots to at least one gallon, or two gallon or five gallons depending on the type of plant, rate of growth. Never bring garden soil into your system, never bring a plant someone has given you. Purchased starts are ok but still a risk. How proficient are you at growing vegetables, plants in a controlled sequestered indoor application? Expect failures at the beginning but LED lighting is not going to work. Go get Shane Smith's greenhouse gardening AND Jorge Cervantes Cannabis Encyclopedia. The best most detailed books you should have and read if you want success of any kind. Hope this helps, please let me know if you need clarification on any of this!!
Go get Jorge Cervantes' The Cannabis Encyclopedia. Everything you need to know about light and plants is in Chapter 17, pages, 253 through 302. This is so well done...oh he gets into PAR big time, how expensive it is just to get a number, turns out it is a pretty useless number, like you said. The most important numbers are the LUMENS (intensity) and CRI (frequency). They have equivalent temperature codes (degrees Kelvin).