Philips Horticulture Lamps
The role of light in the growth and development of plants.
Plant growth (photosynthesis) is not
then determined by lux or energy, but
by the photons from the blue to red
(400–700 nm) part of the spectrum.
This is called growth light!
For the human eye, light is the visible part of
electromagnetic radiation. Most lighting products
are developed for human application. For these
purposes, the intensity of visible light is expressed
in lux. Lux is a photometric unit and is based on
the average sensitivity of the human eye.
The sensitivity is maximized at green/yellow
(555nm) and declines towards longer (red)
and shorter (blue) wavelengths. A lux meter
is corrected for this specific eye sensitivity.
For horticulture, natural daylight (global radiation)
is in most cases measured in terms of energy
(J or W) with a solar meter.This meter is generally
positioned on top of the greenhouse.The value
of global radiation is important for climate and
humidity control in the greenhouse.
Growth Light
Plants have a completely different sensitivity for
colors of light than the human eye. For plant
growth, it is important to define light as small
light particles, also called photons or quantum.
The energy content of photons is different
depending on wavelength (color of light). For one
W of energy, almost twice as many red photons
can be produced compared to blue. In addition to
this, plants are most efficient using the red part of
the light and less efficient using the green and
blue part. In fact, we are dealing with a plant
sensitivity curve for growth light.
Micromol and PPF
Research, both at universities and applied
research stations, has demonstrated that the rate
of photosynthesis is determined by the amount of
photons between 400–700 nm. In scientific terms,
this growth light is called Photosynthetic Photon
Flux (PPF) and is the only reliable measure to clarify
if a light source is suitable for photosynthesis.The
higher the PPF value per Watt, the more efficient
the light source for plant growth.This is the reason
why Philips specifies the PPF value in micromols
per second (µmol/s) for all its light sources for
horticultural use. Philips Green Power and
Agrolite XT lamps are specially developed for
maximum growth light and for this reason, are
among the most efficient light sources available
for horticulture.
Light sensitivity curve of the human eye
Light sensitivity curve of the human eye
400
450
500
550
600
650
700
750
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Wavelength (nm)
Relativ
e
Ey
e
Sensitivity
300
400
500
600
700
800
1.0
0.8
0.6
0.4
0.2
0
Wavelength (nm)
Relativ
e
Quantum
Efficiency
Light sensitivity curve of plants
Light sensitivity curve of plants
Light source as proton emitter
Light particles
or photons (= growth light)
Photosynthesis
Growth light
Carbon
dioxide
Water
Glucose
Photosynthesis process
Photosynthesis process
555
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