PAR is not LUX. DLI is not an instantaneous reading. UV Index is not the same as wavelength-specific UV irradiance. This glossary connects the core terms used across AquaHorti horticulture, indoor-lighting, reef, UV, optical and solar measurement guides.
Each definition explains what the term means, the unit you will commonly see, and the measurement question it helps answer.
Photosynthetically Active Radiation. The traditional plant-light waveband commonly defined as 400–700 nm.
Photosynthetic Photon Flux Density. The number of photons in the selected photosynthetic waveband reaching one square meter each second.
Daily Light Integral. The total amount of photosynthetic light accumulated at a position over the course of a day.
Extended Photosynthetically Active Radiation. A term used for plant-light measurement that extends beyond the traditional 400–700 nm PAR definition.
A way of separating PAR-related photon measurements into red, green and blue spectral regions instead of showing only one total value.
The SI unit of illuminance: visible-light flux weighted for human vision reaching a surface.
An illuminance unit commonly used in the United States.
Correlated Color Temperature. A Kelvin value used to describe the apparent warm-to-cool character of supported white-light sources.
A technical measurement of optical irradiance in the instrument's supported blue-light range.
A simplified spectral visualization intended to provide additional context for supported light sources.
Ultraviolet A. The UV waveband approximately spanning 315–400 nm.
A standardized, dimensionless index describing the strength of sunburn-producing ultraviolet radiation from the sun.
The accumulated amount of UV exposure over time, rather than only the instantaneous strength of the UV source.
Radiant power arriving at a surface per unit area.
A wavelength in the near-ultraviolet region used by some UV LED systems.
A violet / near-UV wavelength widely used by resin 3D-printer light sources.
A deep-red wavelength used by many optical and horticultural light sources.
A near-infrared wavelength commonly used by NIR LED and optical systems.
An underwater correction function used by compatible AquaHorti reef measurement workflows to account for immersion-related sensor response.
Carbon dioxide concentration in the surrounding air.
Relative Humidity. The amount of water vapor in the air relative to the maximum amount the air could hold at the same temperature.
Vapor Pressure Deficit. A vapor-pressure difference derived from temperature and humidity and used to describe the plant-air moisture environment.
The easiest way to choose the right meter is often to understand what two similar-looking measurements do differently.
PAR identifies the traditional 400–700 nm photosynthetic waveband. PPFD quantifies photon flux density within the selected plant-light waveband at a surface.
PPFD is an instantaneous photon-flux-density measurement. DLI accumulates photosynthetic light over the day.
LUX is weighted to human vision and is useful for indoor visible-light illuminance. PAR-related measurements are designed around plant-light photon measurement.
UV Index is a standardized sunlight UV index. UVA irradiance measures radiant power in a defined UVA response range.
CCT gives a single warm-to-cool Kelvin descriptor for supported white light. Spectral information describes how optical power or photon output is distributed across wavelength.
One measurement describes one position. Multiple repeatable points show distribution, hot spots, dark zones and spatial variation.
The glossary defines the language. The four AquaHorti Topic Hubs explain how those measurements are used in real measurement decisions.
Measure light now, light across the day, or the wider growing environment.
Indoor lightingEvaluate brightness, distribution, supported white-light parameters and multi-point measurements.
Reef lightingMeasure at coral level, map the tank, adjust the light and verify the change.
UV / optical / solarSunlight UVI, 385/405 nm UV, 660/850 nm red/NIR, dental curing and solar irradiance.
PAR names the photosynthetically active waveband. PPFD is the photon-flux-density measurement commonly used to quantify plant-relevant light at a surface.
PPFD describes photosynthetic photon flux at a moment. DLI adds the time dimension and describes accumulated photosynthetic light across the day.
LUX is weighted to human visual response and is used for visible-light illuminance. PAR-related measurements count photons in a plant-relevant waveband and answer a different question.
No. A spectrum preview provides a simplified spectral indication for supported sources. It should not be treated as a laboratory spectrometer.
AquaHorti product pages explain the specific instrument. Topic Hubs explain the measurement workflow. The glossary connects the terminology across both.