Aquarium Lighting Calculator

Recommended PAR is set entirely by Plant / Coral Level and Water Type — it takes the midpoint of a target PAR range for your chosen light demand (roughly 15-30 for Low, 35-60 for Medium, 60-120 for High) and multiplies it by 1.5 for Saltwater/Reef (2.5 for the High/SPS-coral tier specifically, since SPS coral needs substantially more intense light than soft or LPS coral) or leaves it at 1.0 for Freshwater. Tank Depth and Tank Length have zero effect on Recommended PAR itself, and Daily Light Integral is calculated straight from Recommended PAR and the plant/water-type-driven Photoperiod, so it too is unaffected by tank dimensions. Photoperiod itself runs the opposite direction from light intensity: higher PAR demand gets a *shorter* recommended photoperiod, not a longer one, because plants and corals saturate photosynthetically after several hours and any additional light beyond that point only feeds algae rather than growth — Freshwater ranges roughly 9-10h for Low down to 6-8h for High, while Saltwater/Reef runs longer overall (roughly 9-12h) since reef photoperiod guidance skews longer than freshwater, but still trends shorter at the high-PAR end of that range. Where tank size actually matters is Surface PAR Needed and Approx. Watts Needed: light intensity is assumed to fall off with depth using a squared correction factor, so a deeper tank needs progressively more surface-level PAR to deliver the same PAR at the substrate.

Approx. Watts Needed then multiplies that surface PAR figure by Tank Length using a rough linear LED-wattage approximation — and of the two tank dimensions, Tank Length moves the wattage estimate more than Tank Depth does for an equivalent percentage change, since length enters as a simple linear multiplier while depth's effect is bounded by the squared correction curve's shape over the input's realistic range. But neither tank dimension is the biggest lever on Approx. Watts Needed overall — switching Plant / Coral Level from Low to High multiplies Recommended PAR roughly fourfold for Freshwater and closer to sevenfold for Saltwater/Reef (since the reef multiplier itself grows for the SPS tier), either way swamping what any realistic change to Tank Length or Tank Depth alone can do. This is a rough planning estimate, not a fixture specification — real LED output efficiency, beam angle, and fixture placement all affect actual delivered PAR in ways this simplified per-inch wattage approximation doesn't capture.