Fluval’s figures for every size
PAR is the light plants can use, measured below the fixture. These are the numbers Fluval publishes on its Plant 3.0 and Plant 4.0 pages; the light falls fast with depth, so the same fixture gives a 12-inch-deep carpet a fraction of what a plant near the surface gets.
| Light | Fits tanks | 3 in | 6 in | 12 in | 18 in |
|---|---|---|---|---|---|
| Fluval Plant 3.0 22W | 15–24 in | 442 | 227 | 80 | not published |
| Fluval Plant 3.0 32W | 24–34 in | 453 | 252 | 107 | not published |
| Fluval Plant 4.0 22W | 15–24 in | 580 | 270 | 110 | 60 |
| Fluval Plant 4.0 32W | 23–35 in | 640 | 290 | 120 | 70 |
| Fluval Plant 3.0 46W | 36–46 in | 470 | 267 | 112 | not published |
| Fluval Plant 3.0 59W | 48–60 in | 545 | 288 | 136 | not published |
| Fluval Plant 4.0 46W | 35–49 in | 700 | 310 | 130 | 80 |
| Fluval Plant 4.0 59W | 46.25–61 in | 750 | 320 | 140 | 90 |
The same lights matched to each common tank size, ranked by the light at the plants →
What the light levels mean
The levels here are the ones Aquarium Co-Op prints on its Easy Green label, which the fertilizer calculator also uses: low light is 10 to 20 PAR, medium 20 to 35 and high 40 and up. Java fern, anubias, mosses and crypts grow in low light; most stem plants, swords and lilies want medium; carpets and red plants do best in high light with CO₂. Low-light plants · Carpet plants · Red plants
Between two depths, and below the last one
Fluval measures at 3, 6 and 12 inches, and the Plant 4.0 also at 18. For a depth in between, we give the figure for the next depth down: the least your plants get straight under the light. Plants toward the front and back glass get less, and so do plants under a glass lid or a dimmed light. Below the deepest figure we don’t guess, because light under water does not fall at an even rate.
Too much light is a problem too
In a shallow tank these lights give far more than a low-tech tank can use, and algae takes the spare light. Both generations dim in the Fluval app: start lower, run the light 6 to 8 hours a day, and raise it as the plants fill in. How long to leave the light on · Planted light fit