Hayley Smith
Supervisor: Dr Erik Murchie
Contents
• What is light and how do plants
sense it?
• The photoreceptors
• The advantages of LED lighting
• Data from:
Preliminary experiments in the
CE growth room
The use of supplementary
lighting in the glasshouse
• Why use LED lighting in VF and UA?
Plant perception of light
Photons are the quanta of light
When emitted from a light source they travel
in waves
The ‘white’ light we see is actually made up of
many colours/ wavelengths
High energy = shorter wavelength
Low energy = longer wavelength
• Plants don’t sense light as a whole but as the
individual wavelengths that the light is made
up of.
• They have individual ‘photoreceptors’;
proteins which absorb light at specific
wavelengths.
• The most abundant photoreceptor is the
green pigment chlorophyll.
• Chlorophyll absorbs photons at
wavelengths of between 400 and 700nm
and channels their energy into the process
of photosynthesis.
400
• Photons at these wavelengths are known as
photosynthetically active radiation (PAR).
700
PAR
Water
Carbon
dioxide
Carbohydrates
Oxygen
Jiao et al 2007
Red/ Far red light photoreceptor:
Phytochrome
Decreased
light induces shade
avoidance syndrome:
• Increased stem elongation and
decreased branching
• Early flowering
Unique effects of UV-A/ blue light (315-500nm)
Photoreceptors: Cryptochromes and Phototropins
Crucial for control of the plant circadian clock.
- Sensing day length and season
- Flowering under control of photoperiod
Repair of photosynthesis molecules and
increased photosynthetic capacity
Increased resistance to some
pests and diseases
Needed for healthy
development and opening of
stomata
Sun leaf morphology
Phototropism
Chloroplast movement
Light emitting diodes (LEDs) allow us to
target the individual photoreceptors
• Narrow band devices that allow us to precisely control not only the
quantity but also spectral quality
• We can deliver just the light energy that the plant needs for optimal
growth and development
Other advantages over conventional artificial lighting:
Last longer
More energy efficient
Can be placed closer to the plants (no heat!)
No warm up/ cool down time
Coriander was grown
under different
combinations of blue, red
and far-red light at
the same light intensity:
PPFD* = 180 µmol m-2 s-1
50%
50%
70%
35%
10%
100%
50%
20%
10%
B at ½
intensity
50%
45%
*The number of photons of PAR that hit an area of 1m2 per second is referred to as the
photosynthetic photon flux density (PPFD).
Height of coriander over time
Electron transport rate (φPSII) day 28
40
35
50%R 50%Fr
30
70%R 20% Fr
10%B
50%B 50%Fr
25
20
100%R
15
10
5
0
0
500
PPFD (µmol m-2 s-1)
1000
Average Height (cm)
ETRm µmol electrons m-2 s-1
45
200
180
160
140
120
100
80
60
40
20
0
50%R 50%Fr
70%R 20%Fr 10%B
70%R 20%Fr 10%B
1/2 intensity
50%B 50%Fr
35%R 10%Fr 55%B
100%R
0
2
4
6
Days after sowing
Leaf area day 36
In the absence of blue light
photosynthetic capacity was
significantly decreased and plants
produced fewer, and thinner leaves.
Average leaf area (cm2)
80
70
60
50
40
30
Increasing blue light resulted in
decreased stem and petiole length.
20
10
0
50%R
50%Fr
70%R
20%Fr
10%B
70%R
20%Fr
10%B 1/2
intensity
Light treatment
50%B
50%Fr
35%R
10%Fr
55%B
100%R
P=<0.05
ANOVA and Bonferroni corrected T-Tests
Summer lettuce
supplemented with blue
(30W LED), red (30W LED)
and white (400W Son-T Agro
HPS) light
• 15 hour days (matching
natural day length)
• Topping up the sunlight
• Altering the spectrum
Cos lettuce under
supplementary red light
had a significantly higher
photosynthetic capacity
and produced the highest
yield (P=<0.05).
Fresh weight Cos lettuce at harvest
Dry weight Cos lettuce at harvest
How could you use LED lighting in a Vertical Farming System?
thebluemarble.org
calibrebio.com
• As the sole source of
light; for the tightest
control of
photomorphogenesis
• To supplement natural
light; to boost
photosynthesis, to extend
day length and/or to
alter the spectral quality
of light that the plants
receive
Why use LED lighting in a Vertical Farming System?
• LED lighting is a highly flexible and energy
efficient means of manipulating plant growth
and development
• At least 20% of the plant genome codes for
proteins that allow the plant to respond to light
• Removing the another environmental variable
for tighter control
• We can give the plant ‘instructions’ with light
• Optimisation of growth and development for:
improved photosynthesis, higher yields, tight
control of time to harvest or flowering,
morphology, improved scent/ flavour
Recipes for different
horticultural plants
Thank you for
listening 
Any
questions?
Thanks to the Murchie lab group and
the Glasshouse staff at the UoN,
Greengage Lighting and the EPSRC
Photon flux density with increasing
wavelength at an irradiance of 1W m-2 s-1
7
Photon flux (µmol-1 m-2 s-1)
6
5
4
3
2
1
0
400
450
500
550
600
Wavelength (λ)
650
700
750
Photons at wavelengths which can
drive photosynthesis (between
400 and 700nm) are known as
photosynthetically active
radiation (PAR).
400
700
All photons enter the
reaction at the energy of
a red photon (680nm)
due to internal
conversion within the
light-harvesting
pigments.
The number of photons of PAR
that hit an area of 1m2 per second
is referred to as the
photosynthetic photon flux
density (PPFD).
UV-B photoreceptor: UVR8
• Exposure to a small amount of UV-B light
(280-315nm) can have beneficial effects!
• Phenolic compounds including flavonoids
• Increased resistance to UV-B light, pests and
diseases
• Changes in colour and flavour and texture