VEGETABLE CROP PRODUCTIVITY AS
INFLUENCED BY LIGHT
Id. No. 35757
Light is the part of the
wavelengths visible to
the human eye (about
390-760 nm) (Moore et
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.
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
Because stems grow toward a source of blue or white
light they are said to have a “positive” phototropic
Conversely, roots are said to have a “negative”
phototropic response because they grow away from a
source of blue or white light.
Charles Darwin, the great
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
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
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
Importance of Light for Plants
Plants use light for:
both simultaneously take place in the
plant and interact with each other.
If photosynthesis is the “engine” providing
photomorphogenesis is the “steering
wheel” to influence the direction and final
It is defined as the ability of light to regulate
plant growth and development, independent of
photomorphogenic include :
Lateral bud outgrowth
Root and shoot growth
Three Principal Characteristics of 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
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.
Plant community can be classified into(Edmond et
Shade plants Partial shade
Slight shade and
light intensity of
Thrive well over
wide range of light
intensity of 20008000 ft-c.
e.g. cabbage, potato,
light intensity of
Light quality refers to the
reaching the plant surface.
Red and blue light have the
greatest effect on plant
Green light is least effective
to plants as most plants
reflect green light and
absorb very little.
Relative efficiency of various light colors in photosynthesis
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
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).
Effect of Light Color on Vegetable Roselle (Hibiscus sabdariffa) growth
Height, h(cm) and thickness, t(mm)
Day 436 nm
13.2 1.8 11.0 1.3 9.0
1.6 10.0 1.6
16.0 1.8 15.0 1.3 11.5 2.0
1.6 11.5 1.6
18.2 1.7 18.0 1.3 14.0 1.8
1.5 12.0 1.5
22.0 1.7 21.0 1.3 17.0 1.8
1.5 13.0 1.4
23.0 1.7 24.0 1.3 18.3 1.8
1.5 14.0 1.4
23.5 1.5 27.0 1.2 19.2 1.7
1.5 14.0 1.3
24.0 1.4 28.0 1.2 20.0 1.7
1.5 17.0 1.3
25.0 1.3 29.0 1.2 22.0 1.6
1.5 20.0 1.3
28.0 1.3 31.0 1.3 25.0 1.6
1.5 21.0 1.3
Yerima et al., 2012
Response of Tomato and Pepper Transplants to
Light Spectra Provided by Light Emitting Diodes
Ratio Light Type
Established Transplants(%) First Yield/ Plant (g)
Javanmardi et al., Shiraz university, Iran, 2013
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)
Long day (short
Short day (long
Require 12-14 hours of
light for flowering.
Require 8-10 hours of
light for flowering.
e.g. tomato, pepper,
vegetable crops, cowpea,
okra, French bean,
e.g. Potato, onion, lettuce,
radish, spinach, beet,
turnip, carrot, etc.
e.g. Sweet potato, Indian
spinach, hyacinth bean,
cluster bean, winged
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.
Plants with tubers (%)
Effect of photoperiod on tuberization in the
Livingstone potato (Plectranthus esculentus)
Allemann et al., 2005
Effect of light on vegetable crops
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.
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.
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,
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
Hills (Grown as LD
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
Tikhomirov et al., 1976 and Sarkar et al., 1978 noticed
that root yield and quality rose with increasing light
intensity in radish.
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
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.
Influence of Light Induced Greening On
Storage of Potato Microtubers
MICROTUBER STORAGE CHARACTERISTICS
Naik and Sarkar , CPRI, Shimla1997
TECHNIQUES FOR REGULATING
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
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
2. Equidistant spacing: Equidistant plant spacing is
more efficient than any other because it decreases light
3. Cultural practices: Weed control may be considered
in part a practice to eliminate competition for light
between crop and weed.
Reducing Light Intensity
Low light plants don’t like high light.
A shade percentage of 30 to 50% is ideal for vegetables.
Effect of tree shading on production of major
Production per plant
Tree – scattered system
Manurung et al., AVRDC Taiwan;November 2008
1. Shade cloth: It is a simple knit or woven fabric
designed to reduce the amount of sun that reaches the
Crop requiring shade cloth are lettuce, broccoli,
cauliflower, peas, celery.
Size of shade cloth : 1.8mx30m, 3.6mx30m, 1.8mx50m,
2. Shading compounds: For sunburn protection at a
field scale, use of film spray-on materials such as
Surround, Screen Duo, and many others.
Different percentages of shade cloth
30% black shade
70% ultra blue
40% black shade
50% black shade
60% black shade
65% ultra red
60% green shade
60% black white
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.
Common HID Light Fixtures Found in
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
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
High-pressure sodium lighting of
greenhouse cucumber in Norway
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.