# Are purple (blurple) LEDs as good as white LEDs?

> Purple (blurple) LEDs grow cannabis about as well as white LEDs at the same PPFD, because photon quantity and efficacy matter far more than colour. White LEDs win in practice: green light reaches lower leaves, you can see deficiencies and pests, and good white fixtures exceed 2.5–3 µmol/J. Judge any LED by its measured PPFD and µmol/J, not its colour.

- Canonical: https://genetixbay.com/knowledge/answers/blurple-vs-white-led.html
- Topic: Environment · Type: Comparison
- Evidence: Supported · 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: Blurple vs full-spectrum white LED | Are red and blue LEDs good for cannabis? | White LED vs purple LED for growing | Is green light wasted on plants?
- 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

At the same [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), purple (red-and-blue) [LEDs](https://genetixbay.com/knowledge/glossary/led.md) grow cannabis about as well as white LEDs: photon quantity and [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) matter far more than colour [1]. White LEDs win in practice: they light lower leaves better, let you **see the plant**, and good white fixtures exceed **2.5–3 µmol/J** [2]. *Supported*.

## Why

Plants use photons across 400–700 nm. Across three cannabis studies, changing the [blue fraction](https://genetixbay.com/knowledge/glossary/blue-light.md) from 4 % to 20 % moved yield only about 12 %, and the authors concluded efficacy was more important for cost [1].

Different LED spectra do change plant shape and chemistry. In one trial two LED spectra gave more compact plants and higher [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) concentrations than [HPS](https://genetixbay.com/knowledge/glossary/hps.md), with equal total cannabinoid yield [3]. Spectrum is a tuning knob, not a yield switch.

Green light is not wasted. Leaves absorb less of it, so it travels deeper into the canopy and drives [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) in lower leaves.

Pink-purple light hides [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) and pests. That alone is a reason to prefer white.

Older blurple fixtures were often sold on "equivalent watts" with low efficacy. Modern red-and-blue diodes can be efficient; check the numbers.

## The numbers

| | White [full-spectrum LED](https://genetixbay.com/knowledge/glossary/full-spectrum.md) | Blurple (red + blue) LED |
|---|---|---|
| Yield at equal PPFD | similar | similar |
| Typical efficacy | 2.5–3+ µmol/J (good fixtures) [2] | varies widely; check the datasheet |
| Lower-canopy light | better (green penetrates) | less |
| Seeing problems | easy | hard |
| Blue fraction | ~5–15 % | often higher |
| Plant shape | normal | more blue = more compact [1] |

**Verdict:** a white LED is the better buy for almost every home grower; a blurple light with a good measured PPFD and µmol/J still grows good plants.

## What to do

1. Compare fixtures by µmol/J and PPFD map, whatever the colour.
2. If you already own a blurple light, keep it and set it by measured PPFD.
3. Inspect plants under white light every few days.
4. Wear rated glasses; bright blue diodes strain eyes.

## Common mistakes

- Choosing by colour story or "full spectrum" marketing.
- Diagnosing leaf colour under purple light.
- Believing a red-heavy "[bloom](https://genetixbay.com/knowledge/glossary/flowering-stage.md)" spectrum is required (*Myth*).
- Running a dim "veg spectrum": low light, not missing blue, causes [stretch](https://genetixbay.com/knowledge/glossary/stretch.md).

## Related

- Full article: [Light spectrum](https://genetixbay.com/knowledge/environment/light-spectrum.md)
- [LED or HPS: which is better?](https://genetixbay.com/knowledge/answers/led-vs-hps.md)
- [What should I look for when buying a grow light?](https://genetixbay.com/knowledge/answers/what-to-look-for-in-a-grow-light.md)
- Terms: [full spectrum](https://genetixbay.com/knowledge/glossary/full-spectrum.md) · [spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md)

## Follow-up questions

**Is green light wasted on cannabis?** No, green light is not wasted on cannabis; that is a myth. Leaves absorb less green than red or blue, but green penetrates deeper into the canopy and drives photosynthesis in shaded lower leaves. Broad white LED spectra, which include plenty of green, grow cannabis as well as red and blue fixtures at the same PPFD and make the plants easier to inspect.

**Why do purple grow lights make it hard to see problems?** Purple grow lights make it hard to see cannabis problems because red and blue light without green distorts leaf colour. Yellowing, pale new growth, rust spots and pests such as mites all look different or disappear under pink-purple light. Growers using blurple fixtures should inspect plants under white light, a headlamp or with the grow light off, every few days.

**Do I need more red light for flowering?** No, cannabis does not need a red-heavy spectrum to flower; that is a myth. Broad white LED spectra with roughly 5–15 % blue flower fine, and HPS at about 4 % blue also works. Research shows yield fell about 12 % as blue rose from 4 % to 20 %, a modest effect, while fixture efficacy in µmol/J matters much more.

## 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