68k what? lumens ? Lumens are simply a measurement of how we perceive light, you must instead look at the micromole rating, also, 8" from a 600w HPS ? The plant would cook. Not a fair comparison.The average HPS kicks out 68k at 8 inches, finding something like that at the LED level is very difficult, thats why hps users smile more ..smile longer but you may wanna look at the
California Lightworks 200w Solarflare
http://www.californialightworks.com/Products_SolarFlare.htm also have the 400w ...but you may have to sell the car