"Full spectrum" has no agreed technical definition. On a grow light it usually means white LEDs (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 (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 colour, spot deficiencies and pests, and judge trichomes 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, 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 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" is unsupported. Controlled trials find intensity and efficacy drive yield; spectrum tweaks mostly change shape. Myth as a potency claim.
An LED (light-emitting diode) grow light uses solid-state diodes to produce light; modern fixtures are the most efficient grow lights, at roughly 2.5–3 µmol/J.Far-red is light from about 700 to 750 nm, just beyond visible red; it adds to canopy photosynthesis when mixed with other light and triggers shade responses like stretch.The first leaves produced by the shoot tip after the cotyledons, with the plant's characteristic serrated leaflets.A nutrient deficiency is a shortage of an essential element in the plant tissue, causing characteristic symptoms; the cause is often pH or uptake rather than an empty feed.A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes.Photon efficacy is how many micromoles of PAR photons a fixture produces per joule of electricity (µmol/J); higher means more light for the same power bill and heat.The process in chloroplasts that uses light energy to turn carbon dioxide and water into sugars and oxygen; cannabis uses the C3 pathway.THC (Δ9-tetrahydrocannabinol) is the neutral, decarboxylated cannabinoid mainly responsible for cannabis's reported intoxicating effects; the living plant makes it almost entirely as THCA.Spectrum is the mix of wavelengths a light source emits, from UV through blue, green, red and far-red; it shapes plant form, while intensity drives most yield.UV-A is ultraviolet light from 315 to 400 nm; plants sense it much like deep blue, and adding it gives no proven gain in yield or potency.Blue light is the 400–500 nm band; it keeps plants compact with shorter internodes and thicker leaves, but a high blue fraction slightly lowers cannabis yield.
