A higher light intensity
stimulates the photosynthesis and there by the production.
here by always was less attention given to the effect that
the spectrum of that light not only had influence on the
photosynthesis, but also on the morphology (the shape of
the plant). The colour of the offered light has effect
on the stretching of the leaf and stems, the leaf stand,
the opening of the stomata, and spouting of the flower
bud and many more processes. This means automatically also
that the bigger the light intensity that you hang up in
artificial light the more of these colour dependable process
you influence with your assimilation light.
Because the spectrum of those vary very much of that of
the spectrum of the sunlight (see fig1) SON-T for instance
has high peaks in greenyellow and orange light, but achieves
bad in blue and red that strongly varies from the natural
in light capturing
In the climate chamber is now researched, financed by
STW, PT and LNV, which influence that had. That was possible
by using a plasma lamp (only recently available on the
market) in combination with filters and additional lamps.
With that the sunlight could be simulated very well (see
fig 2) meanwhile the light intensity stayed under control.
Because for a reliable comparison it has to keep the same
The results are very clear. Young cucumber plants became
64% heavier (dry weight) under artificial sunlight then
under SON-T-light and 128% heavier that under fluorescent
light. That was not because of the photosynthesis per unit
leaf surface, because this was exactly the same at a light
strength of 100 µmol/m² , the applied light
strength during the grow.
What was clearly different; the light capturing. That was
very clear to see from the plants. With fluorescent and
SON-T-light they stayed very flat; on the artificial sunlight
the grow up normal. The sunlight provides – in comparison
with fluorescent and SON-T-light – for longer stems,
longer leaf stems and thinner leaves. The plant invests
more in leave stretching than in leaf thickness. That tells
that the surrounding area increases faster. And that means
more photosynthesis. From the start these plants capturing
more light. Thereby they assimilated more. There by you
get even faster leaf separation, what leads to even more
light capturing. It’s a profit on profit affect.
Thereby there are big differences at the young plants.
At the start the plant clearly grows much faster through
the morphological advantage, caused by the influence of
the light colours.
In a fully grown vegetation this effect doesn’t accure
anymore, because by then all the light is captured. Then
the net-photosynthesis per unit leaf surface is important
first at all and that is –like said- for the 3
The questions of course is now if it’s useful to
hang up this type of artificial sunlight in the glasshouse
instead of SON-T or LED’s (with which you can never
offer a full sunlight spectrum). This questions can not
be answered for this moment.
Especially by pre cultivate or by plant material cultivation
it could be very important. And then especially in light
poor periods, when the effect of artificial light as added
lightning counts the hardest. But for now the most important
advantage in this new technology lies in scientific research.
The research for the influence of coloured LED’s
as added lightning for instance can now take place more
By the way this whole story does not say that results
of earlier scientific test in climate chambers are questionable
now. The understanding of many physiologic processes in
the plant can develop itself without the daylight spectrum
being offered. This stays that way. But in the previous
years became more obvious that light colour has influence
on the shape of the plant. That is now much better to research.
Also the application of a artificial daylight spectrum
can speed up the horticultural research enormously.
Researchers don’t have to do there tests in different
seasons in their glasshouses to research at different day
lengths and daylight intensities. The glasshouse situation
for all seasons is at all time simulatable with an artificial
Recently a British/German company offers a Sulphur Plasma
lamp of which the spectrum comes closer to sunlight then
all the existing lamps. Three quarters sits in the for
the human eye visuable light between 400 and 700 nanometer.
This lamp produces almost no ultraviolet light and just
a little infrared. The basics of the lamp are a bulb Sulphur
(with some other chemicals) that is heated up to a glowing
plasma with micro radiation. The technology was already
developed in the 90’s by NASA and the American ministry
of defense, but knew long time no commercial application.
The website www.plasma-i.com gives a clear view of the
technical status. The system is presented on the Hortifair
To be clear: the spectrum of the lamp was corrected with
filters and extra lamps (by the research team in the Wageningen
universities department of horticulture) to come as close
as possible to actual sunlight.
In tests under artificial sunlight in a climate controlled
room it shows that young cucumber plants grow much better
then under SON-T or TL-light. That’s because the
colour of the light has influence on the shape of the plant.
At the right light colour the young plant is much more
capable of capturing light. Tests with artificial daylight
are only possible since recently. They are in great interest
at the research with coloured LED’s and can speed
up horticultural research.