# 800 W in a 4×4 isn't overkill. For a PR run, it's underkill by a mile

> No, 800–900 W of good LED in a 4×4 ft tent isn't overkill. In a controlled trial, cannabis yield rose in a straight line up to about 1,800 µmol/m²/s with no loss of potency, and 850 W of mid-tier LED only reaches about 1,265. Going from 400 W to 850 W is an estimated 70% more yield. GenetixBay's rule: more light = more yield, if you can remove the heat and match CO₂, climate and feeding. For personal-record runs the founder pushes to 1,800–2,200 µmol/m²/s.

- Canonical: https://genetixbay.com/knowledge/environment/more-light-more-yield.html
- Category: Environment · Level: Intermediate
- Evidence: Supported · Status: Draft: awaiting expert review
- Stage: Veg, Flower · Systems: Any system
- Updated: 2026-11-01 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Is 800 watts too much for a 4x4 grow tent?** No. GenetixBay's house recommendation for a 4×4 ft tent is 800–900 W of dimmable [LED](https://genetixbay.com/knowledge/glossary/led.md) (about 50–56 W/ft²). At 850 W a mid-tier 2.6 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) LED gives about 1,265 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md), still inside the range where a controlled trial found yield rising linearly up to about 1,800 with no loss of potency. Ramp up gradually and match cooling, CO₂, [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) and feeding.

**At what PPFD does cannabis stop responding to light?** Nobody has found the canopy limit yet. In a controlled indoor trial, cannabis flower yield rose in a straight line from 120 to 1,800 µmol/m²/s at ambient CO₂, the top of the tested range, with no plateau. Single leaves level off sooner, around 1,500 at 30 °C in leaf studies, but shaded leaves in a canopy keep gaining. Above about 1,200, CO₂ and climate set the practical limit.

**How much more yield from 400 W to 850 W in a 4x4?** Roughly 70% more, as an estimate. 400 W of a 2.6 µmol/J LED gives a 4×4 about 595 µmol/m²/s and 850 W about 1,265. On the straight-line yield response from a controlled trial (116 [g/m²](https://genetixbay.com/knowledge/glossary/yield.md) at 120 rising to 519 g/m² at 1,800), that's about 230 to 390 g/m². Real results depend on genetics, CO₂, climate and growing skill.

**Does more light lower THC?** No, not in the best evidence. In a controlled indoor trial, raising canopy light from 120 to 1,800 µmol/m²/s multiplied dry flower yield about 4.5 times while [cannabinoid potency](https://genetixbay.com/knowledge/glossary/potency-testing.md) per gram stayed flat. More light buys more grams of equally potent flower, provided the plants aren't stressed by heat or poor climate.

**How many watts for 2,200 PPFD in a 4x4?** Reaching 2,200 µmol/m²/s across a 4×4 ft tent takes about 1,280 W of a top-tier 3.0 µmol/J LED, about 1,480 W of a mid-tier 2.6 µmol/J LED, about 1,675 W of a budget 2.3 µmol/J panel, or about 2,265 W of [double-ended HPS](https://genetixbay.com/knowledge/glossary/hps.md), assuming 85% of the photons reach the canopy. The common 240–400 W advice gives only about 315–685.

**What is the PR zone in cannabis lighting?** The PR (personal record) zone is GenetixBay's name for pushing canopy light to about 1,800–2,200 µmol/m²/s, the founder's line for record runs. At 12 hours, 2,200 µmol/m²/s is 95 [mol/m²/day](https://genetixbay.com/knowledge/glossary/dli.md) of light, past anything published for cannabis, so growers trade intensity against hours. It needs a sealed room with CO₂, strong cooling, VPD control and heavy feeding.

**What are the downsides of running very high light?** In the founder's words, only two: removing more heat, and more trimming at harvest. Every watt adds 3.412 BTU/h, so an 850 W 4×4 adds about 2,900 BTU/h and a 2,200 µmol/m²/s setup about 4,370. High light also needs CO₂, VPD control and feeding to match, and a gradual ramp so the plants adapt.

**Not only is 800 W in a 4 × 4 not overkill: for a PR lab run, it's still underkill, by a mile** (the founder's position) [3].

**Short answer, in plain words.** Plants eat light. Give them more and, as long as the room keeps up, they grow more. In the best controlled trial, cannabis yield rose in a straight line all the way to about **1,800 µmol/m²/s**, the most light they tested, and the buds weren't any weaker [1]. A 4 × 4 ft tent with **800–900 W** of good LED only reaches about **1,200–1,450** of that. So no, it isn't overkill. It's the GenetixBay house recommendation: **more light = more yield, simple as that** (founder's field experience) [3]. The catch is the rest of the room: every extra watt is heat to remove, and high light needs CO₂, climate and feeding to match.

**The deeper version.** Single leaves level off around 1,500 µmol/m²/s at 30 °C, and CO₂ at 750 ppm lifted leaf [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) about 50% [2], but whole canopies keep gaining because shaded leaves are far from saturated [1]. Going from 400 W to 850 W of mid-tier LED in a 4 × 4 moves the canopy from about 595 to about 1,265 µmol/m²/s; on the trial's line that's an estimated **+70%** yield [1]. For personal-record runs the founder pushes to **1,800–2,200 µmol/m²/s**, where "DLI games" begin [3]. That's the gap: **800 W of mid-tier LED gives a 4 × 4 about 1,190 µmol/m²/s**, while the PR line needs about **1,210–1,480 W** of the same light (66–92 W/ft²).

> "Many people call me crazy and say it's overkill, except the ones that follow my advice and are pulling 2.5 grams a watt and packing their tent with pounds of the highest-quality cannabis they've seen." The 2.5 g/W figure is the founder's field experience [3].

**850 W of mid-tier LED in a 4 × 4.** ~1,265: Average canopy PPFD (µmol/m²/s); ~55: DLI at 12 h (mol/m²/day); ~+70%: Estimated yield vs 400 W (From the trial's line); ~2,900 BTU/h: Heat to remove (850 W × 3.412). Source: PPFD = watts × µmol/J × 0.85 ÷ 1.49 m² (85% canopy share assumed); yield line [1]; 1 W = 3.412 BTU/h.

## How much light can cannabis really use? The watts it takes

Cannabis was still gaining at **1,800 µmol/m²/s** in the best trial [1], and the founder's PR line is **2,200** [3]. Here is what it takes at the wall to get there, by fixture tier. *Arithmetic on the fixture efficacies; the 0.85 canopy share is an assumption.*

**Formula:** wall watts = target PPFD × [canopy area](https://genetixbay.com/knowledge/glossary/canopy.md) (m²) ÷ 0.85 ÷ fixture µmol/J. Tiers: old or low-end LED **1.5** (often worse than DE HPS), budget LED **2.3**, mid-tier **2.6**, top-tier **3.0**, and double-ended HPS **1.7** for reference [4][5].

**Let's not kid ourselves: old and low-end LEDs are often worse than HPS.** In the 2014 independent tests, ten LED grow fixtures measured from **0.89 to 1.70 µmol/J**; eight of the ten were below the best double-ended HPS at 1.70, and six were at 1.29 or less [5]. Older-generation and "blurple" panels, and no-name boards built from low-bin diodes driven hard, still sit around **1.3–1.7 µmol/J** in the founder's experience [3]. At **1.5 µmol/J**, 2,200 µmol/m²/s in a 4 × 4 takes about **2,565 W**, more than double-ended HPS (about 2,265 W). Today's DLC-listed fixtures start higher (the 2022 list ran from 1.81 µmol/J up) [4], which is one more reason to buy listed.

**The shock numbers: 2,200 µmol/m²/s in a 4 × 4.** ~1,675 W: Budget LED (2.3 µmol/J); ~1,480 W: Mid-tier LED (2.6); ~1,280 W: Top-tier LED (3.0); ~2,265 W: Double-ended HPS (1.7) (For reference); ~2,565 W: Old or low-end LED (1.5) (Worse than DE HPS). Source: 2,200 × 1.49 m² ÷ 0.85 ÷ µmol/J; efficacies [4][5]; old or low-end tier from independent 2014 tests [5] and the founder's field experience [3]; PR line is the founder's field experience [3].

### Watts per square foot for each target

| Target PPFD (µmol/m²/s) | Old or low-end LED 1.5 | Budget LED 2.3 | Mid-tier 2.6 | Top-tier 3.0 | DE HPS 1.7 |
|---|---|---|---|---|---|
| 900 (typical flower) | 66 W/ft² | 43 W/ft² | 38 W/ft² | 33 W/ft² | 58 W/ft² |
| 1,200 | 87 W/ft² | 57 W/ft² | 50 W/ft² | 44 W/ft² | 77 W/ft² |
| 1,500 | 109 W/ft² | 71 W/ft² | 63 W/ft² | 55 W/ft² | 96 W/ft² |
| 1,800 (trial top) | 131 W/ft² | 86 W/ft² | 76 W/ft² | 66 W/ft² | 116 W/ft² |
| 2,200 (PR line) | 160 W/ft² | 105 W/ft² | 93 W/ft² | 80 W/ft² | 141 W/ft² |

Multiply by 10.76 for W/m².

### Wall watts for a 4 × 4, 5 × 5 and 4 × 8

| Target PPFD | Space | Old or low-end LED 1.5 | Budget LED 2.3 | Mid-tier 2.6 | Top-tier 3.0 | DE HPS 1.7 |
|---|---|---|---|---|---|---|
| 900 | 4 × 4 (16 ft²) | 1,050 W | 685 W | 605 W | 525 W | 925 W |
| 900 | 5 × 5 (25 ft²) | 1,640 W | 1,070 W | 945 W | 820 W | 1,445 W |
| 900 | 4 × 8 (32 ft²) | 2,100 W | 1,370 W | 1,210 W | 1,050 W | 1,850 W |
| 1,200 | 4 × 4 | 1,400 W | 910 W | 805 W | 700 W | 1,235 W |
| 1,200 | 5 × 5 | 2,185 W | 1,425 W | 1,260 W | 1,095 W | 1,930 W |
| 1,200 | 4 × 8 | 2,800 W | 1,825 W | 1,615 W | 1,400 W | 2,470 W |
| 1,500 | 4 × 4 | 1,750 W | 1,140 W | 1,010 W | 875 W | 1,545 W |
| 1,500 | 5 × 5 | 2,730 W | 1,780 W | 1,575 W | 1,365 W | 2,410 W |
| 1,500 | 4 × 8 | 3,495 W | 2,280 W | 2,020 W | 1,750 W | 3,085 W |
| 1,800 | 4 × 4 | 2,100 W | 1,370 W | 1,210 W | 1,050 W | 1,850 W |
| 1,800 | 5 × 5 | 3,280 W | 2,140 W | 1,890 W | 1,640 W | 2,895 W |
| 1,800 | 4 × 8 | 4,195 W | 2,735 W | 2,420 W | 2,100 W | 3,705 W |
| 2,200 | 4 × 4 | **2,565 W** | **1,675 W** | **1,480 W** | **1,280 W** | **2,265 W** |
| 2,200 | 5 × 5 | 4,005 W | 2,615 W | 2,310 W | 2,005 W | 3,535 W |
| 2,200 | 4 × 8 | 5,130 W | 3,345 W | 2,960 W | 2,565 W | 4,525 W |

**Chart: Wall watts a 4 × 4 needs for each light target.** To reach 900 µmol/m²/s a 4 × 4 needs about 525 W of top-tier LED, 605 W mid-tier, 685 W budget or 925 W of double-ended HPS. At the 2,200 PR line it needs about 1,280, 1,480, 1,675 and 2,265 W.

| Target PPFD (µmol/m²/s) | Top-tier LED, 3.0 (W) | Mid-tier LED, 2.6 (W) | Budget LED, 2.3 (W) | DE HPS, 1.7 (W) |
|---|---|---|---|---|
| 900 (typical flower) | 525 | 605 | 684 | 926 |
| 1,200 | 700 | 807 | 912 | 1,234 |
| 1,500 | 874 | 1,009 | 1,140 | 1,543 |
| 1,800 (trial top) | 1,049 | 1,211 | 1,369 | 1,852 |
| 2,200 (PR line) | 1,282 | 1,480 | 1,673 | 2,263 |

Source: Wall watts = PPFD × 1.49 m² ÷ 0.85 ÷ µmol/J; efficacies [4][5].

**Chart: 2,200 µmol/m²/s in a 4 × 4: wall watts by fixture (old or low-end LED needs more than HPS).** Reaching the 2,200 PR line in a 4 × 4 takes about 1,280 W of top-tier LED, 1,480 W mid-tier, 1,675 W budget and 2,265 W of double-ended HPS. An old or low-end LED at 1.5 µmol/J needs about 2,565 W, more than the HPS.

Reference line: DE HPS (2,263).

| Fixture | Wall watts for 2,200 µmol/m²/s (W) |
|---|---|
| Top-tier LED, 3.0 | 1,282 |
| Mid-tier LED, 2.6 | 1,480 |
| Budget LED, 2.3 | 1,673 |
| DE HPS, 1.7 | 2,263 |
| Old or low-end LED, 1.5 | 2,565 |

Source: Wall watts = 2,200 × 1.49 m² ÷ 0.85 ÷ µmol/J; efficacies [4][5]; old or low-end tier [5][3].

### The reverse: what common wattages give a 4 × 4

| Wall watts | Old or low-end LED 1.5 | Budget LED 2.3 | Mid-tier 2.6 | Top-tier 3.0 | DE HPS 1.7 |
|---|---|---|---|---|---|
| 240 W | ~205 | ~315 | ~355 | ~410 | ~235 |
| 400 W | ~345 | ~525 | ~595 | ~685 | ~390 |
| 600 W | ~515 | ~790 | ~890 | ~1,030 | ~585 |
| 800 W | ~685 | ~1,050 | ~1,190 | ~1,370 | ~780 |
| 1,000 W | ~860 | ~1,315 | ~1,485 | ~1,715 | ~970 |

Average canopy PPFD in µmol/m²/s. The common **240–400 W** advice lands at about **315–685 µmol/m²/s** with budget LED or better, and only **205–345** with an old or low-end LED: veg light, at most about 38% of the trial's 1,800 and 31% of the 2,200 PR line. Even **1,000 W** of a top-tier LED stops short of the trial top.

**Chart: What common wattages give a 4 × 4, against the trial top and the PR line.** In a 4 × 4, 240–400 W gives about 205–685 µmol/m²/s depending on the light (old or low-end LED at the bottom, below HPS); 800 W gives about 1,050–1,370 from LED; even 1,000 W of top-tier LED reaches about 1,715, short of the 1,800 trial top and the 2,200 PR line.

Shaded band: Where 240–400 W lands (0–690).

Reference line: Trial top: still rising (1,800).

Reference line: PR line (2,200).

| Wall watts in a 4 × 4 (W) | Top-tier LED, 3.0: Average canopy PPFD (µmol/m²/s) | Mid-tier LED, 2.6: Average canopy PPFD (µmol/m²/s) | Old or low-end LED, 1.5: often worse than DE HPS: Average canopy PPFD (µmol/m²/s) | DE HPS, 1.7: Average canopy PPFD (µmol/m²/s) |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 1,000 | 1,715 | 1,487 | 858 | 972 |

PPFD = watts × µmol/J × 0.85 ÷ 1.49 m²; the 0.85 canopy share is an assumption. The budget LED (2.3) column is in the table above.

Source: Trial [1]; PR line founder's field experience [3]; efficacies [4][5].

## Is 800 W in a 4 × 4 overkill? What the science says

No. **More light = more yield. Simple as that** (the founder's rule) [3]. The common advice of **240–400 W** for a 4 × 4 ft tent can work, but cannabis can use far more light than most growers give it, and the research shows it. *Supported.*

**What the studies found:**

- **Yield kept climbing to the top of the tested range.** In a controlled indoor trial, flower yield rose **linearly** from about 120 to **1,800 µmol/m²/s** canopy PPFD at ambient CO₂, from 116 to 519 g/m², with no plateau in that range. Cannabinoid potency per gram did **not** fall at high light [1].
- **Single leaves level off sooner than whole plants.** In leaf gas-exchange work, cannabis net photosynthesis rose with light up to about **1,500 µmol/m²/s** at 30 °C (86 °F), which was the maximum measured rate; optimum [leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) was **25–30 °C (77–86 °F)** [2]. A canopy keeps gaining past a single leaf's limit because lower and shaded leaves are still far from saturation; the same trial's title says it: yield and leaf photosynthesis "respond differently" [1].
- **CO₂ raises the ceiling.** At 750 ppm CO₂ instead of ambient (350 ppm in that study), leaf photosynthesis rose about **50%** and water-use efficiency about **111%** [2]. More CO₂ and a warm, well-run room let the plants use more light (see [CO₂ calculations](https://genetixbay.com/knowledge/environment/calc-co2-enrichment.md)).

**What each wattage gives in a 4 × 4** (1.49 m², 85% of photons on the canopy, 12 h light; mid-tier 2.6 µmol/J, top-tier 3.0 µmol/J):

| Wall watts | W/ft² | Mid-tier PPFD | Mid-tier DLI | Top-tier PPFD | Top-tier DLI |
|---|---|---|---|---|---|
| 240 W | 15 | ~355 | ~15 | ~410 | ~18 |
| 400 W | 25 | ~595 | ~26 | ~685 | ~30 |
| 600 W | 38 | ~890 | ~39 | ~1,030 | ~45 |
| 850 W | 53 | ~1,265 | ~55 | ~1,460 | ~63 |

PPFD in µmol/m²/s, DLI in mol/m²/day. 240–400 W sits at veg or early-flower light; 850 W of a good LED reaches the range where the trial was still gaining [1].

**Chart: Is 800 W overkill? 4 × 4 wattages against the trial's yield line.** In a controlled trial, yield rose in a straight line from 116 g/m² at 120 µmol/m²/s to 519 g/m² at 1,800, with no plateau. In a 4 × 4, 240 W of mid-tier LED gives about 355 µmol/m²/s, 400 W about 595, 600 W about 890 and 850 W about 1,265, so 850 W sits much further up the same line.

Reference line: Trial top: still rising (1,800).

Marked point: 240 W ≈ 355.

Marked point: 400 W ≈ 595.

Marked point: 600 W ≈ 890.

Marked point: 850 W ≈ 1,265.

| Average canopy PPFD (µmol/m²/s) | Dry flower yield (trial line) (g/m²) |
|---|---|
| 120 | 116 |
| 1,800 | 519 |

Wattage points are mid-tier LED (2.6 µmol/J) in a 4 × 4, 85% on the canopy (assumed); yields on the line are estimates from the trial's endpoints.

Source: Rodriguez-Morrison et al. 2021 [1]; PPFD from PPFD = watts × µmol/J × 0.85 ÷ 1.49 m².

**How much more yield?** Using the trial's linear range as a rough guide (an **estimate**: about 0.24 g/m² more for each extra µmol/m²/s, from the published endpoints [1]):

| 4 × 4, 12 h | Mid-tier 400 W | Mid-tier 850 W | Top-tier 400 W | Top-tier 850 W |
|---|---|---|---|---|
| Estimated yield (g/m²) | ~230 | ~390 | ~250 | ~435 |
| Change from 400 W to 850 W | | **about +70%** | | **about +73%** |

These are estimates from one research setup with one cultivar at ambient CO₂, not a promise. Real yields depend on genetics, training and everything below. The published trial's yields are well below what the founder reports from GenetixBay-advised grows (2.5 g/W, founder's field experience [3]); our [grams per watt](https://genetixbay.com/knowledge/answers/grams-per-watt.md) answer gives the research range. GenetixBay grow journals and [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md) are where members can put numbers on it.

**The conditions for success:**

- **CO₂:** ambient works, but past about 1,200 µmol/m²/s enrichment raises the ceiling [2] (sealed rooms only; see [CO₂](https://genetixbay.com/knowledge/environment/calc-co2-enrichment.md)).
- **Climate:** leaf temperature about 25–30 °C (77–86 °F) under strong light [2]; cooling sized for every watt (see [AC sizing](https://genetixbay.com/knowledge/equipment/calc-cooling-ac-sizing.md)).
- **VPD:** more light means more [transpiration](https://genetixbay.com/knowledge/glossary/transpiration.md); keep VPD in range and the [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) sized for it (see [dehumidifier sizing](https://genetixbay.com/knowledge/equipment/calc-dehumidifier-sizing.md)).
- **Nutrition and water:** faster growth needs feeding and watering to keep up (see [nutrient math](https://genetixbay.com/knowledge/ph-ec/calc-nutrient-dilution-reservoir.md)).
- **Genetics:** cultivars differ in how much light they can use.
- **Ramp up gradually:** 10–15% every 3–5 days, watching the top leaves (see the ramp steps in [lighting sizing](https://genetixbay.com/knowledge/equipment/calc-lighting-sizing.md) and [heat and light stress](https://genetixbay.com/knowledge/environment/heat-light-stress.md)).

## Pushing past 1,500: the PR zone

> **The founder's rule:** **More light = more yield. Simple as that.** If you can remove the heat (which most oversized fans can and will), then **add more light**.

For personal-record runs, even 800–900 W in a 4 × 4 isn't enough for the founder. The line is drawn at about **1,800–2,200 µmol/m²/s** canopy PPFD (founder's field experience) [3]. The research backs the direction: yield was still rising in a straight line at 1,800, the top of the tested range [1].

What that takes in a 4 × 4 (1.49 m², 85% of photons on the canopy, PPFD = watts × µmol/J × 0.85 ÷ 1.49 m²):

| Target PPFD | Top-tier LED (3.0 µmol/J) | Mid-tier LED (2.6 µmol/J) | DLI at 12 h |
|---|---|---|---|
| 1,800 µmol/m²/s | ~1,050 W (~66 W/ft²) | ~1,210 W (~76 W/ft²) | ~78 mol/m²/day |
| 2,200 µmol/m²/s | ~1,280 W (~80 W/ft²) | ~1,480 W (~92 W/ft²) | ~95 mol/m²/day |

**"Playing DLI games."** Around 2,200 µmol/m²/s you start trading intensity against hours (founder's field experience) [3]. At 12 hours, 2,200 µmol/m²/s is **95 mol/m²/day**, well past the 78 that the 1,800 µmol/m²/s, 12-hour top of the published trial delivered [1]; nobody has published where cannabis stops gaining beyond that. So growers in this zone pick a daily total and hit it with PPFD × hours: 2,200 for about 10 hours gives about 79 mol/m²/day, roughly the trial's top. Shortening the light period in flower is safe for flowering (a longer night still triggers it; see [photoperiod](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)); the other lever is trimming intensity in the final weeks. Either way, the plants tell you: bleaching or [tacoing](https://genetixbay.com/knowledge/glossary/taco-leaf.md) at the top means you've passed what they can use.

**Above about 1,200 µmol/m²/s, the room has to keep up:**

- **CO₂:** a sealed room enriched to about 1,000–1,500 ppm; leaf photosynthesis rose about 50% at 750 ppm in the leaf study [2] (see [CO₂ calculations](https://genetixbay.com/knowledge/environment/calc-co2-enrichment.md)).
- **Climate:** leaf temperature about 25–30 °C (77–86 °F) [2], VPD in range, and cooling for every watt: 1,280 W is about 4,370 BTU/h, about 405 [CFM](https://genetixbay.com/knowledge/glossary/cfm.md) of exhaust at a 10 °F rise (see [ventilation](https://genetixbay.com/knowledge/equipment/calc-ventilation-and-carbon-filters.md)).
- **Feeding and water** to match faster growth (see [nutrient math](https://genetixbay.com/knowledge/ph-ec/calc-nutrient-dilution-reservoir.md)).

**The only downsides,** in the founder's words: removing more heat, and more trimming in 8 weeks [3].

**Chart: 800 W vs the PR line in a 4 × 4.** In a 4 × 4, 800 W of mid-tier LED gives about 1,190 µmol/m²/s, well below the founder's 1,800–2,200 PR zone. Reaching it takes about 1,210–1,480 W of mid-tier LED or about 1,050–1,280 W of top-tier.

Shaded band: PR zone: 1,800–2,200 (1,800–2,200).

Marked point: 800 W ≈ 1,190.

Marked point: ~1,480 W.

| Wall watts in a 4 × 4 (W) | Top-tier LED, 3.0 µmol/J: Average canopy PPFD (µmol/m²/s) | Mid-tier LED, 2.6 µmol/J: Average canopy PPFD (µmol/m²/s) |
|---|---|---|
| 0 | 0 | 0 |
| 1,600 | 2,746 | 2,379 |

PPFD = watts × µmol/J × 0.85 ÷ 1.49 m²; the 0.85 canopy share is an assumption.

Source: PR line is the founder's field experience [3]; yield still rising at 1,800 [1].

## Common mistakes

- **Calling it overkill without measuring.** Check canopy PPFD with a quantum meter before deciding a light is "too much".
- **Turning it up without the room to match:** heat, VPD, CO₂ and feeding (see the [grow-room calculations](https://genetixbay.com/knowledge/equipment/grow-room-calculations.md)).
- **Going from seedling to 100% in a day.** Ramp 10–15% every 3–5 days.
- **Reading single-leaf saturation as a canopy ceiling** [1][2].
- **Pushing past about 1,200 µmol/m²/s without CO₂** and then blaming the cultivar.

## Sources

1. Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020
2. Chandra S, Lata H, Khan IA, ElSohly MA. 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299-306. https://doi.org/10.1007/s12298-008-0027-x
3. GenetixBay founder. Field experience (first-hand account; GenetixBay house position).
4. Runkle E. 2022. A closer look at LED efficacy. GPN, January 2022, p. 42. https://greenhousehort.ca.uky.edu/sites/greenhousehort.ca.uky.edu/files/2022-03/LED%20Efficacy.pdf
5. Nelson JA, Bugbee B. 2014. Economic analysis of greenhouse lighting: light emitting diodes vs. high intensity discharge fixtures. PLoS ONE 9(6):e99010. https://doi.org/10.1371/journal.pone.0099010