# LED or HPS: which is better for cannabis?

> LED versus HPS for cannabis quality and yield per photon is an open question at GenetixBay: perhaps. At equal PPFD, research shows similar yields, while LED wins clearly on running cost, about 2.5–3 µmol/J against roughly 1.7 µmol/J for HPS, and on leaf heat load. One small trial found more flower mass under HPS but higher cannabinoid concentration under LED. A Bay Trial will test it.

- Canonical: https://genetixbay.com/knowledge/answers/led-vs-hps.html
- Topic: Environment · Type: Comparison
- Evidence: Contested · Status: Draft: awaiting expert review
- Full article: [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md)
- Also asked as: LED vs HPS yield | Is LED better than HPS for cannabis? | HPS vs LED bud quality | Does HPS give denser buds than LED?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

On running cost, [LED](https://genetixbay.com/knowledge/glossary/led.md) wins: about **2.5–3 [µmol/J](https://genetixbay.com/knowledge/glossary/photon-efficacy.md)** against roughly **1.7 µmol/J** for [HPS](https://genetixbay.com/knowledge/glossary/hps.md) [2]. On yield and quality per photon, the GenetixBay answer is **"perhaps"**: at equal [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) the research shows broadly similar results, the trials are few, and the question is down for a controlled [Bay Trial](https://genetixbay.com/knowledge/glossary/bay-trials.md). *Contested* (house position: open question).

## Why

Photon quantity drives cannabis yield far more than colour. Across three studies, a lower [blue fraction](https://genetixbay.com/knowledge/glossary/blue-light.md) (HPS is about 4 % blue) slightly raised yield, but the authors concluded fixture efficacy mattered more for cost [1].

In a 2018 trial at about 450 µmol/m²/s, plants under HPS were taller and made more flower [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md) than under two LED spectra, while the LED plants had higher [THC](https://genetixbay.com/knowledge/glossary/thc.md) and [CBD](https://genetixbay.com/knowledge/glossary/cbd.md) concentrations; total [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) yield didn't differ [3]. It was small and funded by an LED maker, so treat it as one data point.

HPS puts more radiant heat on the leaf; LED leaves usually run cooler than the air [4]. That changes the climate you need, not just the bill.

## The numbers

| | White LED | HPS |
|---|---|---|
| Efficacy | 2.5–3+ µmol/J [2] | ~1.7 µmol/J [2] |
| Electricity for the same PPFD | ~35–45 % less | baseline |
| [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md) vs air | usually 1–3 °C (2–5 °F) cooler | near air or warmer [4] |
| Blue fraction | ~5–15 % typical | ~4 % [1] |
| Yield at equal PPFD | similar in most work | similar; more mass in one small trial [3] |
| Cannabinoid concentration | higher in one trial [3] | lower in that trial |
| Lamp replacement | none for years | bulbs lose output |

**Verdict:** pick LED for cost, heat and control; whether HPS buds are better per photon is unproven either way, so GenetixBay is testing it in a Bay Trial.

## What to do

1. Compare fixtures by µmol/J and PPFD map, not lamp type alone.
2. Switching to LED? Raise air temperature 1–3 °C and re-check leaf [VPD](https://genetixbay.com/knowledge/glossary/vpd.md).
3. Running HPS? Keep it; just measure leaf temperature and cool accordingly.
4. Want to know for your cultivar? Run a side-by-side at the same PPFD and log grams and lab results.

## Common mistakes

- Comparing an LED at 600 µmol/m²/s with HPS at 1,000.
- Keeping HPS room settings after switching to LED.
- Treating one manufacturer-funded trial as settled.
- Adding [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) "because it's LED" (*Myth*).

## Related

- Full article: [Light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md)
- [Are purple (blurple) LEDs as good as white LEDs?](https://genetixbay.com/knowledge/answers/blurple-vs-white-led.md)
- [Should I run my room warmer with LEDs?](https://genetixbay.com/knowledge/answers/led-grow-room-temperature.md)
- [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md)
- Terms: [LED vs HPS](https://genetixbay.com/knowledge/glossary/led-vs-hps.md) · [Bay Trials](https://genetixbay.com/knowledge/glossary/bay-trials.md)

## Follow-up questions

**Does HPS give better buds than LED?** Whether HPS gives better cannabis buds than LED is an open question; the GenetixBay answer is 'perhaps', and it is slated for a controlled Bay Trial. One 2018 trial at about 450 µmol/m²/s found more flower dry weight under HPS but higher THC and CBD concentration under the LEDs, with equal total cannabinoid yield. Other work finds similar yield at equal PPFD. Evidence is thin.

**Is LED cheaper to run than HPS?** Yes, LED is cheaper to run than HPS for the same light on the canopy. Good current LED fixtures exceed 2.5–3 µmol of photosynthetic photons per joule, against about 1.7 µmol/J for HPS, so an LED needs roughly 35–45 % less electricity for the same PPFD. Less wasted heat also means smaller cooling bills. This part of the comparison is established.

**Do I need to change my grow room settings when switching from HPS to LED?** Yes, switching from HPS to LED changes leaf temperature. HPS radiates heat that warms leaves to around air temperature or above, while LED leaves usually run 1–3 °C cooler than the air. Many growers raise air temperature by 1–3 °C under LED to keep leaf temperature and VPD where they were. Measure leaf temperature with an IR thermometer rather than guessing.

## Sources

1. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://pmc.ncbi.nlm.nih.gov/articles/PMC7987162/
2. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7
3. Magagnini G, Grassi G, Kotiranta S, 2018. The effect of light spectrum on the morphology and cannabinoid content of Cannabis sativa L. Medical Cannabis and Cannabinoids 1(1):19–27. https://doi.org/10.1159/000489030
4. Nelson JA, Bugbee B, 2015. Analysis of environmental effects on leaf temperature under sunlight, HPS and LEDs. PLoS ONE 10(10): e0138930. https://pmc.ncbi.nlm.nih.gov/articles/PMC4598144/