UVA · 315–400 nm
Long-wave ultraviolet
UVA may alter morphology or secondary chemistry, but cannabis responses vary by genotype, spectrum and trial design. Dedicated horticultural diodes often peak around 365–395 nm.
North Blue field guide · Photobiology
UV light in cannabis cultivation
UVA, UVB and UVC are not interchangeable—and “full spectrum” does not automatically mean sunlight. Learn what each band does, what LED, HPS and CMH provide, and where the science remains unsettled.
Explore wavelengths100–400 nmUltraviolet region
315–400 nmUVA · longer wave
280–315 nmUVB · more biologically active
100–280 nmUVC · germicidal range
Wavelength map
Shorter wavelength, higher consequence
Wavelength alone does not define treatment. Dose also depends on irradiance, exposure time, fixture distance, beam pattern and canopy geometry.
Three bands
What the labels mean
UVB · 280–315 nm
Biologically active
UVB can trigger protective and stress responses. Newer controlled studies have not found a reliable commercial potency benefit and have recorded damage at some doses.
UVC · 100–280 nm
Sanitation, not growth
Solar UVC is filtered by the atmosphere. Artificial UVC is germicidal and can injure plants, skin and eyes; it is not a routine canopy-light supplement.
Source matters
LED, HPS, CMH and sunlight
Compare the spectrum reaching the canopy—not the marketing label or color temperature. Manufacturer spectral data or spectroradiometer measurements are more useful than assumptions.
| Source | Typical UV character | Practical meaning | Watch for |
|---|---|---|---|
| White LED | Most standard fixtures have little UV unless dedicated diodes are listed. | UV can be added as a separately controlled channel. | 395–405 nm sits near the UVA/violet boundary; confirm peak and bandwidth. |
| HPS | Generally low UV; output is dominated by yellow, orange and red. | HPS does not recreate natural solar UV. | Lamp and fixture designs vary; check manufacturer data. |
| CMH | Usually more UV than HPS or standard white LED. | A broader spectrum does not prove an ideal UV dose. | Never remove UV-blocking glass or use damaged lamps. |
| Sunlight | Mostly UVA with a smaller UVB component; atmospheric ozone blocks UVC. | Outdoor UV shifts with season, latitude, clouds and elevation. | Greenhouse glazing can filter UVA and UVB. |
Evidence check
UV does not automatically mean stronger flower
Treat UV as an experimental environmental variable—not a guaranteed potency switch.
Historic signal
An older UVB study reported increased THC in drug-type cannabis and helped establish the modern cultivation claim.
Modern trials
Recent peer-reviewed work has not shown a reliable commercially relevant increase in yield or cannabinoid concentration, while some treatments produced stress or damage.
Genotype dependence
Responses can differ among cultivars, and cannabinoids and terpenes do not necessarily respond in the same direction.
Prioritize fundamentals
Stabilize PPFD, photoperiod, temperature, humidity, irrigation, root-zone health and genetics before adding a hazardous variable with uncertain return.
Safety