Plant VS Human lighting terminology

Important lighting termininology, terms and units


Light for Plants

Light for Humans


Photosynthetic Active Radiation

Radation between 400 and 700 nm (nanometer) of the solar spectrum can be used by phototropic organism, like plants to drive photosynthesis. This radation is called photosynthetic active Radiation or PAR.

Visible Light

Radiation between 380 and 740 nm (nanometer) of the solar spectrum is considered as visible light.

The human eye is most sensitive to a yellowish-green color at a peak at 550 nm.


Photosynthetic Photon Flux

Radiation within the range of 400 to 700 nm (PAR) per second.
The PPF Value of a horticulture lamp is measured with an integrated sphere.

Unit:  μmol /s


Luminous Flux

the SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela.

This Value measures the brightness related to the sensivity fo the human eye

Unit: lm


Photosynthetic Photon Flux Density

PPF Radiation / Radiation within the reange of PAR (400-700nm) per square meter (m²)

Unit:  μmol /m²s


Illuminance – light hitting a surface

the SI unit of illuminance, equal to one lumen per square metre.

LUX = Lumen/m²

Unit: lx


How much light (inside the PAR range) do i get per used Watt of electrical energy. Important: this measurement uses the PPF of a lamp and not a ppfd value!

The Efficacy can alter tremendousely, depending on the used spectrum. Red/Blue LED grow lights usually show higher efficacies compared to full-spectrum LEDs. This is caused by different Energy levels of each color/wavelength as well as different efficiency of the available LED chips.


J = Ws

μmol /Ws = μmol /J

Unit: μmol /J


luminous efficacy of a source

How much light  do i get per used Watt of electrical energy

lumen / W

Unit: lumen/W

More about Lighting terminology

Online Efficacy Calculator

Efficacy Calculator

Efficacy Calculator

Efficacy Calculator for Horticulture lighting systems

real consumption, including all losses