seedlings 300 par not enuff?

if leggy, keep upping light. Plant dictates no matter what is "normal" or anecdotal. i find they want nearly full power within 2-3 days of sprouting.. some need a lighter touch, but others scream for more light (stretch) can always place the more sensitive plants in areas of weaker light.. if your umol/s of PAR (PPF) is 300 accross canopy, that's roughly 50% of strength for ambient CO2. 550-600 (assuming 18 hours of operation) is probably the ceiling but this will vary by local variables. Over 12 hours you want closer to 850-900. It's inversely proportional. so if you hamer out what it should be for 18h, it's simply 150% more power for 12 hours to get the same DLI (daily light integral - read the wiki.. it's how you use "PPFD" and hours of operation to determine energy provided) same dli in any common sense context will have the same results, assuming all other factors remain the same