Light

Bro if you got enough $ to buy 20 lights, buy a PAR meter.. cuz in a situation like yours - that’s the only way you can be confident in what you’re getting to your canopy. If you wanna play it cheap, there’s a good app called Photone you can download and pay for a cheap alternative that’s been tested against the apogee PAR meter and falls within 10% error at most.

Hi, Thats not a room that's a 2 stories bus xD There's the issue with Temp and light PPFD. Usually temperature is indicative of how strong the light is but if you face extreme winters and temperatures drop a lot then you won't know if the light is too close just by reading the temperature. Normaly I would say those meters are expensive but you got 20 TS3000 xD. Don't know how they sell those in your country but for mine it comes at +/- 400€ even if I buy 20 xD. You can buy a PPFD meter for less than that. Hope this helps.

Top of leaf canopy should not exceed 86, optimal photosynthesis occurs at 86 farenheight. Temperature is used to determine when a plant will inhibit growth, be sure to keep raising light as plant grows accordingly.

@theuk420show, I never thought about the instruction booklet. Read that it tells you how far to space them and what intensity and heights to have them. Well thought their mate.

40cm as per the mars hydro instruction book you have 20 of them could of read at least one :P

I hope its a big room. Easy way to do it is go off manufacturers height guides. For spacing out you want your light to overlap so start in one corner of the room put the light up at say 40 inch above the pot height. Download a lux app on your phone and place that around your light area let's say 10 inch above pot height, as you move away from the centre your readings will get less. So you want to position the next light so it light strength overlaps creating a fairly even distribution, keep checking the lux until your happy the plants not directly under the light will still get adequate light.