Understanding Par Light - Spectrum Technologies LIGHTSCOUT 3415A Product Manual

Understanding PAR Light

The LightScout
ing PAR light indoors and outdoors regardless of light source type.
It works well for greenhouse, field, and R&D applications requiring
reliable plant growth light readings.
The chemical reaction of photosynthesis requires light. Unlike ener-
gy based light measurements, the quantum (quantity) of photons is
measured since it can be directly tied to the number of these chemi-
cal reactions that can take place. The measure of all available light
between the wavelength (color) range of 400 to 700 nanometers
(nm) has been accepted as the best measure of light available for
photosynthesis. This is defined as quantum Photosynthetic Active
Radiation (PAR) in units of µmol m
light, Quantum light, PPF (photosynthetic photon flux - photons
emitted by a light), and PPFD (photosynthetic photon flux density -
photons hitting a surface) interchangeably, and is the total quantity
of photons in µmoles over the light spectrum from 400 to 700 nm
hitting a one-meter square area every second. One micromole is
equal to 602,214,085,700,000,000 (6.022 x 10
This is not the same as foot candle or lux measurements as shown
in the figures below.
Foot-Candle/Lux Meters
(Human Eye Response)
6
®
Quantum PAR Light Meter is designed for measur-
-2 -1
s . This is referred to as PAR
17
) photons of light!
PAR Meters
(Plant Response)