Transcript effect of light on growth/development

OBJECTIVES
The student will be able to…
• Draw a plant with
a “phototropic
response” to light.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OBJECTIVES
The student will be able to…
• Detail what would need to be done to cause a
poinsettia to flower.
• State how light intensity affects foliage color
and give two examples.
• Describe how latitude, time of year, elevation,
time of day, and region affect light intensity.
• Name several units of light measurement and
specify which is most common in horticulture.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OBJECTIVES
The student will be able to…
• Given a room in which plants will be grown, give a
listing of ten indoor species and where they could
be positioned relative to the windows to receive
the correct amount of light.
• Given a similar room, suggest three ways that the
natural light in the room could be maximized.
• Draw the spectrum of visible light and indicate
the principal wavelengths of importance in
plant growth.
• List two symptoms of excess light in plants
and two symptoms of insufficient light.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
• Light is essential for photosynthesis, and without it,
chlorophyll, carbohydrates, hormones, and many
other plant-manufactured chemicals can’t be made.
– Plants grown in insufficient light do not stop growing
• They develop abnormally long stems with relatively
few leaves, which leads to a stringy or lanky look.
– During etiolation, the plant respires stored carbohydrates.
• When most of the carbohydrate has been respired, it will die.
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Practical Horticulture 7th edition
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Figure 17-1 Etiolation of a plant due to insufficient light. Both plants have the same number of leaves
and were propagated at the same time, but the plant on the right received less light. Kirk Zirion photo.
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By Laura Williams Rice and Robert P. Rice, Jr.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Phototropism and Similar Responses
• Phototropism is the growth
of a plant toward light.
– Auxin is pumped to the side
of the stem away from the
light, which then lengthens.
• Because the sides of the
stem grow at different rates,
the stem curves in the
direction of light.
The “seeking” of light by plants
is actually a hormonal response.
In other plants, differences in
light level change the leaf form.
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Figure 17-2 Phototropism caused by light
reaching the plant from only the left side.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Phototropism and Similar Responses
Cutleaf philodendron (Monstera
deliciosa) shows a different
reaction to varying light levels
The number of splits contained
by new leaves decreases at
lower light levels.
A plant growing in poor light may
have no splits at all, whereas
one growing in moderate light
may have several in each leaf.
Figure 17-3 Splitting philodendron (Monstera
deliciosa) leaves is a function of light intensity.
The unsplit leaf developed in dim light, the
split leaves in brighter light. Rick Smith photo
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light and Flowering - Photoperiod
• Insufficient light intensity can inhibit the flowering
of many plants grown indoors.
– Relatively bright light intensities are necessary
to trigger flowering in most cultivated plants.
• Not often available indoors.
• Plants can be classified with regard to photoperiod
– As short day, long day, or day neutral.
• Photoperiod refers to day/night ratio of each 24-hour
period, affects flowering, tuber & bulb formation.
– Correct photoperiod combined with sufficient light intensity
causes or hastens flowering in some indoor plants.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light and Flowering - Photoperiod
• A few indoor plants, such as chrysanthemum and
poinsettia require specific photoperiods to bloom.
See the entire table on page 322 of your textbook.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light and Flowering - Photoperiod
• Many indoor plants are tropical, from regions near
the equator where day length varies little all year.
– Most are day neutral and flower because of combinations
of age, light intensity, and temperature.
• Time a photoperiodic plant must be kept under
correct day/night lengths to trigger flowering varies.
– If not maintained long enough, the plant may revert to
its vegetative state, ceasing bud development..
– A short-day plant on a long-night schedule too long will
lose valuable photosynthetic time and may lose vigor.
– Schedule should be maintained until the flower buds
are completely developed.
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Practical Horticulture 7th edition
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light and Flowering - Photoperiod
• Most houseplants in which photoperiod controls
flowering are short-day plants, needing daily periods
of uninterrupted darkness before flowering occurs.
– Darkness should be checked by standing inside with the
door closed—cover leaks or use another closet.
– Poinsettias are very sensitive, and bloom will be delayed
if the dark period ever is broken by light, or is not absolute.
• Flowering long-day plants are simply left in a room
used in the evenings.
– Artificial lights supplement the natural day length with
enough light to total 14 or more hours, and blooms
will be initiated.
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light and Plant Health - Foliage
• Foliage Color - in many instances the darker the
foliage of a plant, the less light it requires.
– Common plants that grow well in dim light—snake
plant, rubber plant, cast iron plant, Chinese evergreen,
and philodendron—all have deep green foliage.
• When grown with little light, they develop a dense chlorophyll
layer near leaf surfaces, making them efficient users of light.
• Many, such as variegated spider plant, tricolor
dracaena, and variegated wandering Jew, require
more light than their nonvariegated relatives.
– Lacking chlorophyll in the white areas of the leaves, they
require more or brighter light to compensate.
• Many plants with red coloring pigments also need bright light.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light and Plant Health
• Fleshy/Succulent Plants with thickened leaves
and/or stems such as jade, kalanchoe, and cacti
require more light than do those with thin leaves.
– Fleshy structure minimizes surface area vulnerable to
transpiration water loss, helping survive in dry climates.
• Photosynthesizing area is reduced, so these plants can be
grown indoors more successfully in bright-light locations.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light and Plant Health - Native Conditions
• A plant that grows naturally in the shade of other
plants is usually better adapted to indoor growing
than a plant accustomed to unobstructed sunlight.
– Ferns grow naturally in the shade of trees, and also
grow well in a dim area indoors, a generalization for
many tropical plants.
• Devil’s ivy, peperomia, and arrowhead.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity
• Natural light intensity is affected by geographical
or altitudinal variation, and climatic factors.
– Light intensity and duration are factors contributing
to the total light a plant receives.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity - Latitude
• Latitude - due to the way the Earth is oriented in
space, the sun rises exactly in the east, and sets
exactly in the west only at the equator.
In the Northern Hemisphere, the sun will
always appear slightly in the southern sky.
Figure 17-4a Typical positions of the sun in (a) winter and (b) summer in the Northern Hemisphere.
Note the sun remains in the South and that the positions of rising and setting differ with the season.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity - Latitude
• By hitting Earth’s atmosphere at an angle instead of
directly above, the distance light must travel through
the atmosphere to reach the Earth is increased.
– Light is lost in the atmosphere & the further north one
lives, the less the light intensity.
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Practical Horticulture 7th edition
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity - Time of Year
• The sun stays in the southern sky over the year, and
drops lowest toward the southern horizon in winter.
– Approaching closest to directly overhead at midday in
summer, with the change in angle dependent on the
distance from the equator.
Figure 17-4a Typical positions of the sun in (a) winter and (b) summer in the Northern Hemisphere.
Note the sun remains in the South and that the positions of rising and setting differ with the season.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity - Time of Day
• Midday, the sun at its highest point, provides the
greatest intensity of light.
– In either morning or evening the sun is lower toward
the horizon & intensity decreases due to the distance
it is penetrating through the atmosphere.
• Local daily weather variation can change intensity.
– Out West, foggy mornings lessen early-day light intensity.
• The afternoon sun is much brighter in these areas.
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Practical Horticulture 7th edition
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity - Altitude
• People living at high altitudes (over 1,000 feet above
sea level) frequently receive greater light intensity
than would be expected at their latitude.
– Air is less dense, the atmospheric layer is thinner at high
altitudes, and less light intensity is lost passing through it.
• Denver, Colorado, at over 5,000 feet in altitude, has
substantially higher light intensity, year-round than
Boston, Massachusetts
– Even though the two are less than 4 deg latitude apart.
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Practical Horticulture 7th edition
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity - Clouds, Fog, and Smog
• In cloud-, fog-, or smog-covered areas, light intensity
is habitually lower than clear areas.
– Water vapor or pollution haze acts as a reflector,
sending much of the sunlight back toward space.
• They also diffuse sun rays, giving the Earth shadowless
illumination, not a sun/shadow pattern of direct sunlight.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Intensity - Snow/Sand
• Persistent snow cover affects light intensity by
reflecting sunlight indoors.
– Cold areas with snow cover most of the winter receive
a slightly increased amount of light through all windows
because of this reflection.
• This principle applies to houses surrounded by lightcolored sand, white rock mulch, or similar material.
– Although dark soil will absorb light, light sand reflects
it and will increase the light entering a house.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Duration
• Light duration (day length) is another component of
total light.
– Increased duration can help compensate for low intensity,
but below a certain minimum, will not help.
• Equatorial days & nights are equal in length all year.
– In the North, 9 hour winter days & 15 hour summer
days are not uncommon, as a result of latitude.
• More pronounced the further north one travels.
• The shortest winter days correspond with the period
when the sun is lowest on the horizon —reaching a
climax around December 22, the winter solstice.
– At this point the sun again begins moving toward the
northern sky and days begin to lengthen.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Light Duration
Coding the continental U.S. into
bright-, medium-, and dim-light
areas for winter and summer.
Bear in mind that for most areas,
summer light is three to four
times as great as winter light.
Figure 17-5b Mean daily solar radiation
throughout the U.S. in January and July.
University of Texas Libraries.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
• Measuring light in relation to plant growth is a
complex topic that can be broken into three
subtopics:
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Finding Total Solar Radiation Entering Windows
• Total light entering windows is of great importance.
– Measure with a thermopile or bolometer with a flat
response—not favoring reading any partiular wavelength.
• It is an incident light meter because it measures light intensity
falling on an object, in this case a plant.
– A representative reading takes measurements at several
parts of the plant, aiming the meter at the light source.
– Readings need to be taken several times a day, and under
cloudy and sunny conditions to determine average light.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Finding Total Solar Radiation Entering Windows
• In some cases light requirement of a species will
be listed in foot-candles, an old measurement.
– Illumination of a surface 1 ft from a standard candle.
• Comfortable light for reading is 50 foot-candles, and
bright summer daylight is about 10,000 foot-candles.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Finding Total Solar Radiation Entering Windows
• The USDA classified over 100 houseplants by their
light requirements:
– 75 to 200 foot-candles (767 - 2,153 luxes) is deemed low.
– 200 to 500 foot-candles (2,153 - 5,382 luxes) is moderate.
– 1,000+ foot-candles (10,764 luxes) is high.
• Compensation-point intensities—below which
respiration exceeds photosynthesis—evaluated as:
– 25 foot-candles (229 luxes) for low-light plants
– 75 to 100 foot-candles (767 - 1,076 luxes) for mediumlight species.
– 1,000 foot-candles (10,764 luxes) for high-light types.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Window Direction
• Unobstructed south-facing windows receive the
longest duration of daily direct sunlight all year
in the northern hemisphere.
– Windows receive sun midmorning to late afternoon.
• East/west-facing windows provide an intermediate
amount of light, less than south, more than north.
– In western states, west-facing windows may provide
more total solar radiation than in eastern states.
• North-facing windows provide the least light but are
are acceptable for growing a number of species.
– Dimness results from the lack of direct sun, only light
reflected from the ground or nearby buildings.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Factors Decreasing Window Entry of Sunlight
• Overhanging or wide eaves can decrease the time
or distance direct sunlight enters a room.
– They shade the window when the sun is high in the sky,
at midday, and several hours before and after.
This effect is more pronounced
in the summer than in the winter
because the sun is higher off the
southern horizon.
Figure 17-6 Effect of eaves on the amount
of sunlight entering through a window. Note
the depth of penetration into the room.
(a) with eaves; (b) without eaves.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Factors Decreasing Window Entry of Sunlight
• Tall buildings or fences close to windows can also
decrease direct sunlight, a problem of shading
from the south, east, or west.
– Unlike blockage due to eaves, the problem will be more
pronounced in winter.
• Shrubs or trees planted close to a window can limit
light entry, at times reducing it to only reflected light.
– Deciduous trees and shrubs will defoliate in fall, and cause
little blockage of light during the crucial winter months.
– Evergreens exclude light continuously, and removal or
pruning of the plants is the only solution.
• Limb up or thin trees
• Shrubs should be thinned & headed back to minimize blockage.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Factors Decreasing Window Entry of Sunlight
• Most homeowners open curtains or shades in the
morning and close them after dark.
– Valuable early-morning light can be lost this way.
• East-facing windows can lose a substantial portion of their
direct sunlight when curtains remain closed after sunrise.
– When curtains are open, they can decrease the light
area around the outside edge of the window.
• Hang curtains so they expose the entire window area
when open & avoid valances, which block overhead light.
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Practical Horticulture 7th edition
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EFFECT OF LIGHT ON GROWTH/DEVELOPMENT
Factors Decreasing Window Entry of Sunlight
• Low-Emittance (Low-E) Window-Glazing Materials
have been designed to allow for high solar heat gain,
moderate, or low heat gain depending on climate.
– Coating a glass surface with a low-emittance material
blocks a significant amount of heat from entering.
• Low-E coatings are transparent to visible light and
transmit 59 to 78% of the light striking the window.
– Compared to 81% for normal double-pane windows,
and 90 to 95% for single-pane, uncoated glass.
• Sufficient for most indoor plants, although it might affect
high-light-requiring species and seedlings.
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Practical Horticulture 7th edition
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PLACEMENT FOR OPTIMAL NATURAL LIGHT
• Plants can be classified as bright-, medium-, or dimlight-requiring & should be positioned within a room
to satisfy their requirements.
• The minimum light level at which a plant can
maintain itself is called the compensation point.
– Light received is enough to photosynthesize carbohydrate
for respiration, with no surplus carbohydrate for growth.
• With less light, the use of carbohydrate for respiration will
exceed its rate of manufacture, and the plant will die slowly.
• Decorative plants can be bought at the desired size
& maintained in good condition with the correct light.
– As the plant is growing very slowly if at all, the time
devoted to maintenance is minimal
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PLACEMENT FOR OPTIMAL NATURAL LIGHT
Bright Light
The designation “bright”- or “high”light-requiring is given to a number
of plants including most flowering
species, cacti, and succulents.
Difficulty in providing them with
sufficient sunlight during darker
winter months is the main problem.
It is nearly impossible to give brightlight-requiring plants too much light.
Most adjust readily to full sunshine
and will grow vigorously outdoors
during warm weather after they
have been acclimated.
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Practical Horticulture 7th edition
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See the entire table
on textbook page 327.
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PLACEMENT FOR OPTIMAL NATURAL LIGHT
Bright Light
While light conditions vary
greatly depending on locale,
as a general rule, bright-light
plants should be placed no
farther than 3 feet from
a southern window or 2 feet
from an east or west window.
Figure 17-7 Suggested distances from windows
for growing bright-, medium-, and dim-light plants.
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PLACEMENT FOR OPTIMAL NATURAL LIGHT
Moderate Light
• Most foliage houseplants have moderate- or
medium-light requirements.
Adequate light is provided if they
are placed up to 6 ft from a southern
window, 4 ft from east/west windows,
or up to 2 ft from a north window.
Moderate-light users grow better
when close to the glass, especially
in winter.
As summer approaches, those in
south or west windows should be
watched for symptoms of excess
light & moved back if symptoms
should appear.
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Practical Horticulture 7th edition
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See the entire table on
textbook page 328.
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PLACEMENT FOR OPTIMAL NATURAL LIGHT
Low Light
• Only a small percentage
of indoor plants will grow
satisfactorily in low light.
A number of species classified
as moderate-light requirers can
survive low-light conditions for
several months, unharmed.
They will live well in moderate
light but generally should not
be grown in bright light.
Some low-light plants can
be injured by excess light.
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Practical Horticulture 7th edition
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MAXIMIZING NATURAL LIGHT
Rotation
• Plant rotation is proven commercially, and is also
practical for the home gardener.
– Many large foliage plants in lobbies & malls are rented
from interior landscaping & plant maintenance specialists.
• Every few months the plants in the low-light display area are
replaced and taken back to the greenhouse for recuperation.
• During rotation in the greenhouse, they accumulate
carbohydrate for respiration when the display area.
– The home gardener can move some plants closer to
windows and others farther away every 2 to 3 weeks.
• This works best on fairly hardy indoor plants & moderateor low-light-requiring species; less so on high-light plants.
• Plants in bud should not be moved, as the sudden change
in environment can cause the buds to drop.
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Practical Horticulture 7th edition
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© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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MAXIMIZING NATURAL LIGHT
Reflective Colors
• Once light enters a window, contact with plants can
be maximized by light-colored walls, carpets, and
drapes which bounce, rather than absorb light.
– White walls reflect up to 90% of the light & can contribute
significantly to the amount of light plants receive.
• Increased reflected light makes it possible to grow moderateand especially low-light-requiring plants farther from windows.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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MAXIMIZING NATURAL LIGHT
Skylights
• Skylights are a nearly ideal solution to the problem
of insufficient light indoors for growing plants.
– Once a very expensive custom construction item, they
now are available prefabricated in many sizes/materials.
Translucent glass or plastic
breaks incoming light rays
at the point at which they
pass through the material
Enables it to illuminate a
larger area over a longer
time than clear glazing.
Figure 17-8 Light penetration patterns
in transparent and translucent skylights.
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Practical Horticulture 7th edition
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ARTIFICIAL LIGHTING FOR PLANT GROWTH
• The indoor gardener using artificial lighting can grow
almost any flowering plant successfully, as well as
herbs, vegetables, and transplants for outdoor use.
– Light gardening, as it is called, can be a fascinating hobby.
• Two basic types are used for artificial lighting of
plants in homes—incandescent & fluorescent lights.
– LED (light-emitting diode) lights have come on the market
in the past few years and are being used in commercial
installations such as hydroponics.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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ARTIFICIAL LIGHTING FOR PLANT GROWTH
Photosynthetically Active Radiation (PAR)
• The last characteristic addressed is the amount
of the types of light necessary for plant growth.
– An understanding of the makeup of light, and kinds
of light necessary for plant growth is necessary for
a gardener to purchase lighting equipment wisely.
• Sunlight is naturally suited for plant growth—some
artificial light is not.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Photosynthetically Active Radiation (PAR)
• Light energy is divided into wavelengths
– Show here is the relationship between wavelengths
of visible light and other types of radiant energy.
Figure 17-10
The radiant
energy spectrum.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Photosynthetically Active Radiation (PAR)
• Of the energy types listed, only three—ultraviolet,
visible, and infrared rays (heat)—are contained in
solar radiation and are significant to plant growth.
Figure 17-10
The radiant
energy spectrum.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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ARTIFICIAL LIGHTING FOR PLANT GROWTH
Photosynthetically Active Radiation (PAR)
• Ultraviolet light causes tanning, and plants growing
outdoors are exposed to it all day.
– It is not necessary for plant growth, and UV light
does not pass into glass greenhouses.
• Infrared waves transmit heat by traveling through
air/space & warming whatever objects they contact.
– Infrared in sunlight warm plants outdoors during the day.
• At night infrared rays will be given off from previously warmed
surfaces like the soil.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Photosynthetically Active Radiation (PAR)
• Light in the orange-red and blue-violet portions of
the visible light spectrum have the most significant
influence on plant growth.
Figure 17-10
The radiant
energy spectrum.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Photosynthetically Active Radiation (PAR)
• Visible light wavelengths compose the majority of
photosynthetically active radiation—termed PAR
ranging from 400 to 700 nanometers.
– The Green and yellow wavelengths are commonly
reflected by plants.
• Giving them their characteristic green appearance.
– The Orange-red light and blue-violet light are used
in photosynthesis.
– The red light wavelength has proven to be the range
that triggers flowering in photoperiodic plants.
• Whereas blue-violet light is responsible for phototropic
responses.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - Incandescent
• Incandescent lights produce light by channeling
electricity through a wire, which heats up and glows.
– Compared to fluorescent lights, incandescent lights use
more electricity to produce the same amount of light, the
extra energy being given off as heat.
High in orange-red wavelength,
but low in blue-violet, giving objects
they light a warm appearance.
Red-orange is useful for flowering plants
and makes an attractive spotlight, lack of
blue-violet makes normal incandescent
bulbs alone unsatisfactory for plants.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - Incandescent
• Incandescent lights produce light by channeling
electricity through a wire, which heats up and glows.
– Compared to fluorescent lights, incandescent lights use
more electricity to produce the same amount of light, the
extra energy being given off as heat.
Plants grown only under incandescent
lighting are paler, thinner, and more
etiolated than plants grown under the
other light sources listed.
In addition, they will not branch, and
flowering & subsequent senescence
are very rapid.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - Fluorescent
• Household-Type Fluorescent Lights are long tubes
used in specially designed light fixtures.
– The inside of the tube is coated with phosphorescent
material and has an electrode at each end.
• By a chemical reaction with mercury, electricity stimulates
the phosphorescent coating to give off light.
– They give off almost no heat from the tubes, and
only a small amount from the control ballast.
– Initially more expensive, fluorescent lights are more
economical to operate than incandescent lights.
• Up to five times as much light from the same wattage.
• They have a much longer life than do incandescent bulbs.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - Fluorescent
• Wavelengths of light emitted by fluorescent tubes
vary depending on the blend of phosphorescent
materials used to coat the tube.
– Of the normal fluorescent tubes, cool white has been
used most often for growing foliage plants.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - Fluorescent
• Characteristics of plants grown under cool white
light are richly colored foliage, slow stem elongation,
and proliferous branching.
– A sturdy, bushy, and, therefore, attractive plant.
However, it is poor in
orange-red and should
be supplemented by
an incandescent light
for flowering species.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - Plant Lights
• Plant lights are commonly available in incandescent
and fluorescent styles.
– Plant lights are sold in fewer numbers than normal
fluorescent tubes, so they are more expensive.
Designed to provide light in
both blue-violet & orange-red
wavelengths, in the best
combination for plant growth.
Most are of the economical,
higher intensity fluorescent
type.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting
Figure 17-11 Light emitted
from four types of artificial
lighting. A nanometer is
one millionth of a meter.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
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ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - LED
• LED ( light-emitting diode) plant lights can save
money even over fluorescent lights.
– LEDs do not have a ballast as do fluorescent lights.
• They operate on less than 20 volts at the bulb, compared
to the regular 110 for conventional lights.
• There is very little heat produced and no reflector.
Grow Master lights
use 6 to 9 watts
of electricity, and
last 10 to 12 years
operated 24 hours
per day
Figure 17-12 LED plant lights. Photo courtesy of SolarOasis Inc.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Types of Lighting - LED
• LED plant lights produce light targeted to the parts
of the spectrum that plants use.
– Provides additional energy savings over conventional
grow lights since no electricity is used for light that
is of no benefit to the plant.
• LED plant lights deliver light photosynthetically valuable
to plants, but relatively dim when perceived by the eye.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Setting Up a Fluorescent Light Garden
• More than one tube is generally needed to grow
bright-light-requiring plants such as flowering
species and annual or vegetable transplants.
– A minimum of two (preferably four) tubes, side by side.
• Tubes of 40 watts or more are best, not over 3” apart.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Setting Up a Fluorescent Light Garden
• A homemade light garden is not difficult to construct.
– A widely used setup is a shop light containing two tubes
and a built-in reflector.
• The fixture is mounted on a metal stand or shelving unit,
and a lamp timer regulates the hours of operation.
Detailed diagrams
for homemade light
gardens are plentiful
in light-gardening
and home-building
project books and
websites.
Figure 17-13 A simple fluorescent light setup for flowering plants.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
ARTIFICIAL LIGHTING FOR PLANT GROWTH
Growing Plants under Lights
• Success of a light garden is largely determined by…
– Distance from the tubes at which plants are grown and
number of hours per day lights are on.
Because fluorescent lights do not
give off heat, there is no problem
of heat damage to plants placed
too close to the bulbs
Figure 17-14
A full spectrum fluorescent
plant light for tabletop use.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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ARTIFICIAL LIGHTING FOR PLANT GROWTH
Growing Plants under Lights
• In general, 12 to 16 hours per day is considered
suitable if there is no additional source of light.
– Although foliage plants can grow with less, there is no
advantage to running the lights a shorter time except
for controlling the photoperiod.
• Although fluorescent light bulbs may appear to burn
out spontaneously, they actually lose intensity slowly
over their entire lifetime of 12,000 or more hours.
– Replace bulbs after about 75% of stated hour-life, as
the intensity will have decreased by 15 to 20 percent.
• Replacing one bulb every 3 or 4 months will avoid excesslight symptoms from the sudden intensity increase.
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Practical Horticulture 7th edition
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LIGHT-RELATED INDOOR PLANT DISORDERS
Insufficient Light
• Etiolation of new growth, yellowing and dropping
of the older leaves also usually occur.
– Plants in the advanced stages of light deficiency have
thin weak stems and few leaves.
• Such plants should be placed under increased light
to recuperate.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
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LIGHT-RELATED INDOOR PLANT DISORDERS
Excess Light
• A plant occasionally will develop symptoms of
chronic excess light exposure—such as a lowlight plant grown in a south-facing window.
– New leaves will be small and a pale yellowish-green.
• Short internodes give a compact, unhealthy appearance.
• A more common case is acute excess light damage
that occurs when houseplants are placed outdoors
after growing indoors all winter.
– Sudden increase in intensity destroys the top layers of
cells on the leaf surfaces & leaves acquire a silvery cast.
• The silvery cast turns brown or bleached yellow in a few days.
– Sunburned leaves do not heal—the only way to improve
the plant’s appearance is removing them.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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LIGHT-RELATED INDOOR PLANT DISORDERS
Excess Light
• Bright-light plants will benefit from summer sunlight,
but medium-and dim-light species should be placed
in shaded or filtered sun areas.
– To acclimate houseplants to outdoor conditions, place
them in a sheltered outdoor location that receives early
morning or late afternoon sun.
• After another week bright-light plants can be moved to
a brighter outdoor area but still should receive protection.
• When bringing the plants indoors again, the
acclimatization procedure should be reversed.
– Gradually adjusting the plants to decreased indoor light
will prevent leaf drop and other signs of light deficiency.
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
END OF
CHAPTER
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Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
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