Looking for opinions regarding lights

** the umol/s, ppfd and dli stuff is accurate no matter what light you buy. The stuff about efficacy and how to determine if a light has good efficacy is only accurate for the LM301 diode. Any other diode you'd have to check their spec sheet on the original manufacturer's site, not the ligh manufacturer's site. the light manufacturer's tend to lie and misuse the metrics in retarded ways to manipulate more sales. umol/s of PAR per m^2 (PPFD) relative to hours of operation is what you want to focus on. It should add up to 35-40 DLI (daily light integral, see wiki). per sq ft it's something like 75-85umol/s per sq ft to add up to upper 30's DLI over 12 hours. Once you calculate 1 dli combo, you can just factor by proportion of hours changed. e.g. for 18hours i can simply take 2/3rds of that 12 hour figure. So, 18hours is 50-57umol/s per sq ft. if you convert that to m^2 by multiplying by 10.76ft^2/1m^2, that is "PPFD", and you can use that value to reference any DLI table with hours of operation to find DLI. Working backward from DLI can give you the targets i suggested. All neat and tidy. Local variables matter as far as how much DLI you can provide compared to someone else, so it will not often be exactly the same as what other people do in their garden. atmospheric co2 and VPD are part of this equation, too. 25sq ft x 57 = 1425 umol/s to get upper 30s DLI over 18 hours of operation 1425 * 18/12 = 2138 umol/s for 12 hour operation. This would cover photoperiod if you want to retain that option for the future. As long as the light you choose provides roughly the umol/s suggested above, it'll be sufficient for a 5x5 tent. LED do dim over time. the hotter they run, the faster they die. So, efficacy of any light in question needs to be known to guesstimate just how much you've lost wiht heavy use over 3 years. Hours of use accumulate faster with autoflowers, therefore years of use will be a bit lower, too. The 50,000hours before it is 90% of original brightness advertised specification is dependent on running the diodes at .2watts per diode. if you divide watts by number of diodes and it's a much higher value your light will dim faster than advertised. A cooling fan may help, but regardless it will have diminished life, which makes itmore difficult to guesstimate. unless you tooke a lux or umol/s reading from a specified spot and distance when you first turned on, it amounts to a guess. Otherwise you could take a 2nd reading from that exact same spot and know exactly how much it has dimmed since then. Even if running "hot" should be a good 20-30k hours before you have eto worry too much about dimming. You'll see different growth pattern, too. Slowly over time your normal hanging distance will result in longer internodes, all other factors the same. Bottom line: If exclusively growing autoflowers, any light with 1400umol/s will be excellent for ambient CO2 conditions. If growing photoperiods or want the option to fill that 5x5 tent with them occasionally, you want 2100 umol/s for ambient CO2 conditions. At this point you can just focuse on other characteristics -- good heat sink, high efficacy. Efficacy is king. that's what you pay for. If a product has a high price and piss-poor efficacy, you are paying for a brand name and not anything beneficial for the extra cost. .2watts per diode is the goal.. this math is 'close enough' considering 3-5% of the diodes will not be the standard LM301 white diode. can teach a person to fish or give them an answer. If you have to ask for an answer everytime, that's just being a burden. Learn how to think about it correctly, and you can easily discern which light you want to buy now and in the future.

I'd be looking ideally at about 750w bar light to fill your space. A 640w would work if its all you can afford. Over 800w in 25 sq ft of space would be overkill unless you plan to run CO2. Be sure to choose a reputable brand as all lights are not made the same.