I have 13 of these in 3 veg/flower tents and 2 prop/cloning tents, which requires a range of wattages.
My recco is 240w per light, for max wattage range depending on footprint size, look at the mapping.
and the “a” version dimmer, these lights need dimmers....and the “a” version gives max dimming range
A dedicated or detachable dc meter is nice to have as well, like
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I use a single hlg-240h-54a per 96... an example of how this flexibility comes in handy is in this situation
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Where this is very handy
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if you have heat issues wire your setup with the drivers located outside the tent.
Get a light meter, even if just a cheap lux meter like this (for 96elite, divide lux by 64 to get ppfd)
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Check out page 16 of this, for ppfd levels (and other useful targets) at various devel stages:
http://fluence.science/wp-content/uploads/2016/09/High-PPFD-Cultivation-Guide-9.27.16.pdf
As for parallel or serial, i’ll leave that to the electricians here...i prefer max flexibility, so for me, only one driver per light, with disconnect connectors, on inexpensive aluminum rails...plug and play, position anywhere, anytime...in seconds. Goes really well with this small form factor.