600w hps is good for a 3ft x 3ft - 1m x 1m tent (though often used in 4ft x 4ft too)
For a 3ft x 3ft space you want about 320w LED For a 1m x 1m you want 360w LED
For a 4ft x 4ft you want at least 480w but I'd still use a 600w LED of good efficiency.
if you buy an led, in my opinion, you want to buy one thats got more light then you nreed and a dimmer on it, it saves the longgevity of the light, as its not running at 100 %, should last you twice as long as running a smaller light at 100%