# Full spectrum

> Full spectrum is a marketing term for a grow light with broad output across the visible range, usually a white LED, sometimes with added red, far-red or UV.

- Canonical: https://genetixbay.com/knowledge/glossary/full-spectrum.html
- Also written: full-spectrum LED, full spectrum light, broad spectrum, white LED spectrum, sunlike spectrum
- Glossary category: Environment and light · Evidence: Supported
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

"Full spectrum" has no agreed technical definition. On a grow light it usually means white [LEDs](https://genetixbay.com/knowledge/glossary/led.md) (blue chips coated with phosphor) that emit continuously from about 420 to 700 nm, often with extra red diodes near 660 nm, and sometimes [far-red](https://genetixbay.com/knowledge/glossary/far-red.md) (730 nm) or UV-A (385–405 nm) channels. It is used to contrast with older "blurple" fixtures that had only narrow red and blue peaks.

## In practice

White-dominant fixtures are easier to work under: you can see [true leaf](https://genetixbay.com/knowledge/glossary/true-leaves.md) colour, spot [deficiencies](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) and pests, and judge [trichomes](https://genetixbay.com/knowledge/glossary/trichome.md) without guessing. That alone is a good reason to choose one. Spectrally, broad white light also includes green photons, which penetrate deeper into the canopy than red or blue because leaves absorb them less strongly.

What "full spectrum" does not guarantee: high [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md), a useful far-red fraction, or any UV at all. Read the spectral graph and the µmol/J figure on the datasheet. No fixture reproduces sunlight exactly, and none needs to.

## Don't confuse with

- **Spectrum**: the general concept; every lamp has one.
- **Blurple**: red and blue only fixtures; efficient for [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) but poor for inspecting plants.
- **Colour temperature**: a 3,000 K or 4,000 K label describes appearance, not plant response.

## Myth check

"Full spectrum means more [THC](https://genetixbay.com/knowledge/glossary/thc.md)" is unsupported. Controlled trials find intensity and efficacy drive yield; spectrum tweaks mostly change shape. *Myth* as a potency claim.

## Related terms

[Spectrum](https://genetixbay.com/knowledge/glossary/spectrum.md), [LED](https://genetixbay.com/knowledge/glossary/led.md), [Far-red](https://genetixbay.com/knowledge/glossary/far-red.md), [UV-A](https://genetixbay.com/knowledge/glossary/uv-a.md), [Blue light](https://genetixbay.com/knowledge/glossary/blue-light.md)

## Read more

- [Light spectrum: blue, red, far-red and UV, what's real](https://genetixbay.com/knowledge/environment/light-spectrum.md)

## 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://doi.org/10.1371/journal.pone.0248988