2. LIGHT
Light is the part of the
electromagnetic
spectrum having
wavelengths visible to
the human eye (about
390-760 nm) (Moore et
al. 2003).
3.
4.
All life on earth is supported by the radiant
energy of the sun.
Light is one of the most important and variable
components of the plant environment.
The visible spectrum, a small portion of UV and
infrared sections, comprise the wavelengths that
are most significant for plants.
5. Phototrophic Movement of Plant
Plants sense and respond to their environments in a
number of ways. Receptor molecules within plant
cells perceive changes in external conditions, such as
light.
Because stems grow toward a source of blue or white
light they are said to have a “positive” phototropic
response.
Conversely, roots are said to have a “negative”
phototropic response because they grow away from a
source of blue or white light.
7. Charles Darwin, the great
evolutionary
biologist,
investigated grass seedlings’
growth responses to blue
light as early as 1881.
He already knew that
growing plants would bend
toward light coming from a
single direction.
Darwin
and
his
co
investigator son, Francis,
proposed that the seedlings
were bending toward light
in response to an “influence”
that was transported down
the stem from the growing
tip.
8.
In 1926, Fritz Went, a Dutch scientist, identified the
chemical messenger that causes cells on the shaded
side of a shoot to elongate and grow faster than cells
on the lighted side, thereby bending the stem toward
the light source. He called this messenger hormone
auxin.
9. Importance of Light for Plants
1.
2.
Plants use light for:
Photosynthesis
Photomorphogenesis
both simultaneously take place in the
plant and interact with each other.
If photosynthesis is the “engine” providing
the
energy
for
plant
growth,
photomorphogenesis is the “steering
wheel” to influence the direction and final
plant appearance.
11. Photomorphogenesis
It is defined as the ability of light to regulate
plant growth and development, independent of
photosynthesis.
Plant
processes
that
appear
to
be
photomorphogenic include :
Internode elongation
Chlorophyll development
Flowering
Abscission
Lateral bud outgrowth
Root and shoot growth
13. Three Principal Characteristics of Light
Quantity (Intensity)
◦ Photosynthesis
Quality (Wavelength)
◦ Photomorphogenesis
Duration
◦ Photoperiodism
14. QUANTITY
Light
quantity refers to the intensity or
concentration of sunlight and it varies with the
season of the year.
The more sunlight a plant receives (up to a point),
the better capacity it has to produce plant food
through photosynthesis.
Light quantity can be decreased in a garden or
greenhouse by using shade-cloth.
It can be increased by surrounding plants with
white or reflective material or supplemental lights.
15. Plant community can be classified into(Edmond et
al.,1964) :
Shade plants Partial shade
and sun
plants
Sun plants
Slight shade and
direct sun
tolerant plants
Require low
light intensity of
500-1000 foot
candles.
Require high
light intensity
of 3000-8000
ft-c.
Thrive well over
wide range of light
intensity of 20008000 ft-c.
e.g. tomato,
brinjal, chilli,
all cucurbits,
peas and
beans, sweet
potato, etc.
e.g. cabbage, potato,
etc.
Require
moderately high
light intensity of
1000-3000 ft-c.
16. QUALITY
Light quality refers to the
colour
or
wavelength
reaching the plant surface.
Red and blue light have the
greatest effect on plant
growth.
Green light is least effective
to plants as most plants
reflect green light and
absorb very little.
18. RED LIGHT
Red and orange light triggers hormones in plants that
increase flowering and budding, but plants cannot
grow with red light alone and also need blue light.
It stimulates flowering and foliage growth, but too
much red light will cause a plant to become spindly.
It also induces germination and blue light promotes
seed growth, but far-red light inhibits germination.
HPS (high-pressure sodium) lamp emit a red orange
glow and are excellent companion lights for growing
conditions.
19. BLUE LIGHT
Blue light, referred to as cool light, encourages
compact bushy growth.
Blue light regulates many plant responses including
stomata opening and phototropism.
Metal halide grow lights emit more light in the blue
spectrum and are the best source of indoor lighting to
use for plant growth if there is no sunlight available.
Blue light is considered an important factor in the
formation of chlorophyll and chloroplast development
(Akoyunoglo and Anni, 1984).
20. Effect of Light Color on Vegetable Roselle (Hibiscus sabdariffa) growth
Height, h(cm) and thickness, t(mm)
Day 436 nm
h
t
470nm
h
1.7 7.1
t
490nm
520nm
546nm
578nm
700nm
h
t
h
t
h
h
t
h
t
1.7
8.2
1.7
t
1
8.7
1.3 6.5
2.0
6.2
1.7
7.5
1.6 5.2
2
13.2 1.8 11.0 1.3 9.0
2.0
11.0
1.6
12.5
1.6 10.0 1.6
12.0 1.7
3
16.0 1.8 15.0 1.3 11.5 2.0
12.0
1.6
13.5
1.6 11.5 1.6
16.2 1.8
4
18.2 1.7 18.0 1.3 14.0 1.8
14.5
1.6
16.5
1.5 12.0 1.5
19.0 1.8
5
22.0 1.7 21.0 1.3 17.0 1.8
15.5
1.5
20.0
1.5 13.0 1.4
22.1 1.7
6
23.0 1.7 24.0 1.3 18.3 1.8
15.7
1.5
22.5
1.5 14.0 1.4
24.9 1.7
7
23.5 1.5 27.0 1.2 19.2 1.7
15.8
1.5
23.5
1.5 14.0 1.3
28.1 1.6
8
24.0 1.4 28.0 1.2 20.0 1.7
16.8
1.5
24.0
1.5 17.0 1.3
29.2 1.6
9
25.0 1.3 29.0 1.2 22.0 1.6
23.5
1.4
25.0
1.5 20.0 1.3
30.4 1.5
10
28.0 1.3 31.0 1.3 25.0 1.6
24.8
1.4
26.0
1.5 21.0 1.3
32.4 1.4
Yerima et al., 2012
21. Response of Tomato and Pepper Transplants to
Light Spectra Provided by Light Emitting Diodes
Ratio Light Type
White
Red
3
0
2
Established Transplants(%) First Yield/ Plant (g)
Blue
Tomato
Pepper
Tomato
Pepper
0
82
78
1177
156.30
1
0
90
84
1507
161.00
1
2
0
95
93
1753
155.30
0
3
0
100
98
2440
178.70
2
0
1
95
91
1603
155.30
1
0
2
95
95
1720
143.30
0
0
3
100
100
2307
104.30
0
2
1
100
100
2693
192.00
0
1
2
100
100
2530
180.00
Javanmardi et al., Shiraz university, Iran, 2013
22. DURATION
Light duration or photoperiod refers to the amount of
time that a plant is exposed to sunlight.
Based on response to light period , plants may be
classified into :
Long day plants ( 12-14 hours)
Short day plants (8-10 hours)
Day neutral plants (photo insensitive)
23. Day neutral
Long day (short
night)
Short day (long
night)
No preferential
photoperiod for
flowering.
Require 12-14 hours of
light for flowering.
Require 8-10 hours of
light for flowering.
e.g. tomato, pepper,
eggplant, cucurbitaceous
vegetable crops, cowpea,
okra, French bean,
amaranth, etc.
e.g. Potato, onion, lettuce,
cabbage, cauliflower,
radish, spinach, beet,
turnip, carrot, etc.
e.g. Sweet potato, Indian
spinach, hyacinth bean,
cluster bean, winged
bean, etc.
24.
Day length and light intensity also influence crop
water requirements. In general, the greater the
intensity of light, the greater the rate of
transpiration or water loss from the plant and the
greater will be the need to replace the water loss.
25. Plants with tubers (%)
Effect of photoperiod on tuberization in the
Livingstone potato (Plectranthus esculentus)
100
90
80
70
60
50
40
30
20
10
0
10
10.5
11
11.5
12
12.5
Photoperiod (hours)
13
13.5
14
Allemann et al., 2005
26. Effect of light on vegetable crops
Cucurbits
In case of cucurbits, day length and intensity of
light coupled with temperature are known to
influence sex expression.
In cucumber an abundance of light tends to
increase the number of staminate flowers.
On the other hand , reduction of light increases
the number of pistillate flowers.
Crops such as watermelon, cantaloupe and
honeydew melons require high light intensity
and warm temperatures to produce good
growth and high sugar content in their fruit.
27. Tomato
High light intensity accompanied by high temperature
is harmful to fruit set.
Reduction of light intensity by shading increases fruit
set significantly at high temperature.
Mehta and Bhavamaryana, 1981 found that red light
and far red light induced carotenoid synthesis,
particularly lycopene in ripening fruits of tomato cv.
Marglobe.
28. Capsicum
Short day conditions (9-10 hours light)
stimulated plant growth and increased the
productivity by 21-24% , beside improving the
quality of capsicum (Egorova, 1975).
Reduction of solar radiation by 50% increased the
fresh weight of whole fruit (Bigotti, 1974).
Number of days from sowing to flowering and
percentage of flower drop increased as the shade
increased. But capsaicin content was not affected
by different shade intensities (Jeon and Chung,
1982).
29. Potato
The intensity & duration of light is responsible for
higher yield & quality of tuber due to increased
photosynthesis but tuber must remain covered
under the soil to avoid sun scalding and greening.
Plains (Grown as SD
In India
Tuber initiation
early
Hills (Grown as LD
Tuber initiation
delayed
during winters)
during summers)
Murti, 1975
30. Root crops
Sulgin et al., 1963 in radish reported that maximum
shoot growth occurred in plants exposed to low light
intensity , but fresh weight of the whole plants, leaves,
stems and roots increased with increasing light
intensity.
Tikhomirov et al., 1976 and Sarkar et al., 1978 noticed
that root yield and quality rose with increasing light
intensity in radish.
31. Bulb crop
In onion and garlic for vegetative growth lower
temperature and short photoperiod are required,
while relatively higher temperatures and long
photoperiod are needed for bulb development.
Mann, 1952 also found that long days and high
temperature encouraged bulb development in
garlic.
32. Leafy vegetables
In spinach, long days and warm weather are very
favorable for quick bolting of the crop.
In Amaranthus; A. caudatus, A. cruentus and A.
edulis are short day species, while A.
hypochondriacus is reported to be day neutral.
33. Influence of Light Induced Greening On
Storage of Potato Microtubers
60
50
(%)
40
30
Control
Greened
20
10
0
Biomass loss
Sprout emergence
MICROTUBER STORAGE CHARACTERISTICS
Naik and Sarkar , CPRI, Shimla1997
34. TECHNIQUES FOR REGULATING
LIGHT INTERCEPTION
The control of light is significant part of the
technology of horticulture. The quality, intensity,
and duration of light has manifold effects on the
many physiological processes of the plant.
Light interception can be increased or decreased by
many ways.
35. Increasing Light Interception
It depends on:
1. Geographic location: The duration and intensity of
light depend on climate and geography.
Crops planted in rows oriented east and west utilize
light more effectively than those planted north and
south.
2. Equidistant spacing: Equidistant plant spacing is
more efficient than any other because it decreases light
competition.
3. Cultural practices: Weed control may be considered
in part a practice to eliminate competition for light
between crop and weed.
36. Reducing Light Intensity
Why shade?
Low light plants don’t like high light.
Reduce temperature.
A shade percentage of 30 to 50% is ideal for vegetables.
Shade cloth
Artificial
Shading
methods
Natural
Shading
compounds
Tree shade
38. Effect of tree shading on production of major
solanaceous crop
1600
Production per plant
(in gram)
1400
1200
No shading
Medium light
Low light
1000
800
600
400
200
0
Egg plant
Chilli
Tomato
Tree – scattered system
Manurung et al., AVRDC Taiwan;November 2008
39. Artificial shade:
1. Shade cloth: It is a simple knit or woven fabric
designed to reduce the amount of sun that reaches the
vegetable bed.
Crop requiring shade cloth are lettuce, broccoli,
cauliflower, peas, celery.
Size of shade cloth : 1.8mx30m, 3.6mx30m, 1.8mx50m,
3.6mx50m
2. Shading compounds: For sunburn protection at a
field scale, use of film spray-on materials such as
Surround, Screen Duo, and many others.
40. Different percentages of shade cloth
30% black shade
cloth
70% ultra blue
shade cloth
40% black shade
cloth
50% black shade
cloth
60% black shade
cloth
65% ultra red
shade cloth
60% green shade
cloth
60% black white
shade cloth
41. Types of Supplemental Light Sources
Incandescent lamps: It produces a continuous spectrum
from blue to infrared. The greater part of overall emission
is in the invisible infrared.
Fluorescent lamps: Light from ordinary fluorescent lamps
is low in red and deficient in far red. Now special
fluorescent lights are available that will produce light richer
in red. More efficient than incandescent.
High Intensity Discharge (HID) lamps: Their use is
increasing in greenhouses, despite the relatively high cost
of fixtures and installation.
43.
High pressure sodium
lamps: It yield red visible
light as well as small
portions of all other visible
light. They are used for
the reproductive or
flowering phase of the
vegetable growth.
LED (Light Emitting
Diode) : The newest type
of grow lights use LED
technology. It grow lights
maximize blue and red
light to provide and
excellent balance for
plants.
High-pressure sodium lighting of
greenhouse cucumber in Norway
44. Conclusion
There are many countries in which water and land are
scarce. So, by using different colored lights on
vegetable crops can help to get higher yield with
minimum use of valuable resources.
The improvement of productivity under low light
conditions can be done by using artificial sources, thus
extending the production season into the winter
months of the year.
