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Measurement Values Explained
Learn about PAR, PPFD, DLI, Illuminance, and CCT
Photone allows you to measure different properties of light. Most measurements (all except from CCT) are light intensity measurements. Meaning they indicate how much light hits on a surface.
PPFD (PAR Meter)
Photosynthetic photon flux density (PPFD) describes how much photosynthetically usable light your plant receives at this very moment. PPFD is typically measured in micromoles of photons (i.e. light particles) per square meter per second (μmol/m²/s). This is what PAR meters or quantum meters usually display.
PAR
Photosynthetically active radiation (PAR) describes the wavelengths (i.e. colors) of light that plants use for photosynthesis. PAR comprises photons with wavelengths between 400 and 700 nanometers (nm).
DLI
The daily light integral (DLI) describes how much photosynthetically usable light your plant receives over the entire day, given the light remains at the same intensity for the time configured. Set the photoperiod (i.e. amount of hours your lamp is running) to get the correct DLI.
Illuminance
Illuminance is measured in lux or foot-candle (fc) and describes how much light, as perceived by humans, reaches a surface. The total light output of a lamp (i.e. its radiant flux) is measured in lumen (lm). Lux (lm/m²) is how many lumen reach a square meter whilst foot-candle (lm/ft²) describes lumen per square foot.
Illuminance should not be used when measuring light for plants. Learn why on the Photone blog:
CCT
Correlated color temperature (CCT) refers to the color appearance of a light source and is measured in Kelvin (K). In other words, the CCT describes how "warm" or "cool" a light appears. For example, a lower CCT like 2700K describes a warm, yellowish light. A higher CCT such as 6500K describes a cool, bluish light.
The CCT is an important factor in plant lighting as it can influence a plant’s properties during various growth stages such as flowering and fruit production, leaf size and thickness, and the overall plant shape and structure.
The sun's CCT varies throughout the day, ranging from warm reddish-orange light (2000-3000K) at sunrise and sunset, to cooler white light (5500-6500K) at midday. This natural cycle occurs due to changes in the sun's position and the amount of atmospheric gasses its light travels through.
Other Metrics
You might have heard of other plant lighting-related metrics such as ePAR, PPE, PPF, YPF, YPFD, or the McCree curve. Head over to our blog and have a look at the full grow light metrics glossary:
