Low cost lights? Che consumino poco (sotto i 10pw ...

the most efficient light you can get is ~2.7-3.0umol/J (j/s = w/s) you need 500ppfd to properly flower a photoperiod plant over 12 hours. 500ppfd is simply umol/s relative to 1 m^2. Smaller space requires less umol/s to reach "500 PPFD" so, this estimate will be relative to 1m^2 and you can do the algebra to apply to your space. 500umol/s from your like. if ~2.8umol/J, that is a minimum of 180Watts. This would be a fixture using Samsun LM301 dioes... anything else would make the above false. you'd also need enough diodes... if the fixture has roughly 0.4watts per diode or less, it's good. otherwise, it won't reach the advertised efficacy. So, if oyu have .5m^2.. you'd want ~90 watts. 2m^2 you'd want a minimum of 360 watts. these are minimums, but you'd want more. 50-60% more would be the ceiling with ambient CO2 and some headroom to ameliorate dimming over 60,000 hours of use (~80% intense after 60k hours, so if you can increase ~25% you can maintain same exact coverage the entirity of that 60k hours) Hence, overshooting a bit is a good idea. So, find a light with LM301 diodes... enough that watts/# of diodes =< 0.4watts per diode. Match watts with growing space and you are rocking at the lowest wattage you can find on the market... this is a mathemetical certainty.