LED Grow Lighting Glossary

Dimming is the ability of a lighting system to intentionally reduce light output and power consumption in response to a control signal (such as 0–10 V, digital, or networked controls), enabling light-level adjustment, energy savings, and operational flexibility.

Input voltage is the allowable range of electrical supply voltage a lighting system is designed to accept and operate within (for example, 120–277 V or 347–480 V), and is a key consideration for compatibility with facility power infrastructure and electrical codes.

Max ambient temperature is the highest surrounding air temperature at which a lighting system is designed to operate continuously while meeting specified performance, safety, and reliability requirements.

Photosynthetic Photon Efficacy (PPE) measures how efficiently a grow light converts electrical energy into usable photons (PPF) and is expressed as micromoles per joule (µmol/J).

Photosynthetic Photon Flux (PPF) is the total number of photosynthetically active photons (400–700 nm) emitted by a light fixture each second, measured in micromoles per second (µmol/s).

Power is the rate at which electrical energy is consumed by a lighting system, typically measured in watts (W), and is a key input when evaluating energy use, operating cost, and photon efficacy.

Far-red light refers to wavelengths typically between 700–750 nm that influence phytochrome signaling, flowering response, and canopy penetration.

A photon is a discrete packet of light energy; plant responses are driven by photon quantity and wavelength, not perceived brightness.

Photosynthetically active radiation (PAR) is the portion of the light spectrum—from 400 to 700 nanometers—that plants use to drive photosynthesis.

Spectrum refers to the distribution of photon output across wavelengths, influencing both photosynthesis and plant morphology.

Ultraviolet light is radiation below 400 nm that is not included in PAR but may influence secondary metabolite production and plant stress responses.

Wavelength is the distance between light waves, measured in nanometers (nm), and determines photon energy and spectral classification.

Chlorophyll is the primary photosynthetic pigment responsible for absorbing light—primarily blue and red wavelengths—to drive photosynthesis.

Cryptochrome is a blue-light photoreceptor involved in circadian rhythms, stem elongation, and leaf expansion.

Photo-bleaching or photo-oxidation refers to light-induced plant stress caused by excessive photon density or improper spectral balance.

Photomorphogenesis describes plant growth and development responses regulated by light quality, direction, and duration, rather than light quantity alone.

Photoperiod is the length of light and dark cycles within a 24-hour period and plays a key role in flowering, vegetative growth, and dormancy.

Photoreceptors are specialized plant proteins that detect specific wavelengths of light and trigger physiological responses.

Photorespiration is a metabolic process in which oxygen competes with CO₂ during photosynthesis, reducing carbon fixation efficiency.

Photosynthesis is the biochemical process by which plants convert light energy, water, and CO₂ into carbohydrates used for growth and metabolism.

Phytochrome is a photoreceptor sensitive to red and far-red light that regulates flowering, shade response, and plant architecture.

Stomata are microscopic openings on leaf surfaces that regulate gas exchange, transpiration, and CO₂ uptake.

Carbon dioxide is a primary input for photosynthesis, with elevated concentrations often increasing photosynthetic efficiency when adequate light is available.

Daily Light Integral (DLI) is the total amount of photosynthetically active radiation delivered to a plant canopy over a 24-hour period, expressed in mol/m²/day.

Photosynthetic Photon Flux Density (PPFD) is the amount of photosynthetically active light (400–700 nm) reaching a surface each second, measured in µmol/m²/s.

Relative humidity is the amount of water vapor present in the air compared to the maximum amount the air can hold at a given temperature, expressed as a percentage (%), and it directly influences plant transpiration, disease pressure, and environmental control.

Vapor Pressure Deficit (VPD) is a measure of the air’s drying power and influences transpiration, nutrient uptake, and overall plant stress.

The DesignLights Consortium (DLC) is an independent organization that establishes performance, testing, and reporting requirements for energy-efficient commercial and horticultural lighting systems.

Environmental Location Rating

Environmental location ratings—commonly expressed as dry, damp, or wet—are third-party certified classifications that define the types of environments in which an electrical or lighting product is permitted to operate safely under applicable electrical codes.

An IP rating indicates how well a fixture is sealed against dust and water ingress; IP ratings describe enclosure sealing only and are not equivalent to third-party certified environmental ratings such as dry, damp, or wet location listings.

Q90 is a reliability metric indicating a fixture is expected to maintain at least 90% of its initial photon output after a specified number of operating hours, based on tested component performance.

UL 8800 is a safety standard specific to horticultural lighting systems that addresses electrical, mechanical, thermal, and environmental risks.