On handout #2, schedule based on planting outside 6/1
Jaderloon - top greenhouse construction company in world. www.jaderloon.com
Lighting for Plant Growth by Bicknell
very good book on plant
lighting
*****
Lighting
High pressure mercury lamps
Has spectrum similar to
fluorescents
Distinctive bluish light
Efficiency rating of about
13% of electricity used is given off as light
Available in power ratings
up to 1000 watts
High pressure metal halide lamps
Up to 2000 watts
Available power rating is 20%
of electricity used
Cost more than mercury
lamps
Output deteriorates over
time faster than other lamps
Excellent spectral output
Doesn't give
"funny" color to plants
Good for retail
areas
High pressure sodium
Most widely used in US
Cheaper than mercury lamps
Wide spectrum
Light concentrated in
yellow-orange part of the spectrum
Maximum efficiency is 25%
400 and 1000 watts
Up to 24,000 hour lifespan
Compare with
10,000 hour lifespan of mercury)
Low pressure sodium
Available in 35 to 180
watts
180 watts best
for greenhouse
Most efficient of all lamps
= available power rating of 27%
Life expectancy is 18,000
hours
Less heat than from other
lamps
Can be placed
closer to plants
Has limited spectrum and
not suitable for some crops
Pure yellow light
Causes pale green color in
lettuce, petunias, African violets
Also low blue levels:
morphological changes (ie strap-shaped leaves in lettuce)
These problems can be cured
by adding 10% light from incandescent or the sun.
Photoperiod (see handout #4)
Flowering is controlled by light
Hortocultural crops are classified according to their response to
photoperiod = each photoperiodically sensitive plant has a critical night
length
1. Short day plants =
nnyctiperiodism - flowers only when critical night length has been exceeded
eg cattleya, orchids,
kalanockoe
2. Long day plants = hemeroperiodism
= flowers only when the dark period is shorter than the critical night length
eg tuberous begonia,
hibiscus species, spinach
3. Day neutral - flower reguardless
of night length
but do need enough light
for photosynthesis
eg African violets, roses
4. Quantitative long day plants =
partial hemeoperiodism
Initiate flower buds under
any day length, BUT
time to
flowering is shortest when critical night length is not exceeded = long day
response
eg carnations, salvia
5. Quantitative short day plants =
partial nyctiperiodism
initiates flower buds under
any day length, but faster when critical night length is exceeded = short day
response
eg cosmos, zinnias,
cinerarias
(cosmos: 15.5
hours for 2 weeks to initiate flower buds)
6. Quantitative temperature &
photoperiod interaction
Plants are short day or
long day or day neutral at one temperature but different response at another
temperature
eg snapdragons, petunia =
quantitative long day at high temperatures, but day neutral at lower
temperatures.
eg poinsettia is short day
at high temperatures and long day at low temperatures.
Basically photoperiod control comes in
forms
1. Short night treatment
lengthening the day period
with artificial lights
a. prevents flowering in short day plants
b. promotes flowering in long day plants
Lights are turned on at the
end of the day or in the middle of the night
If you have a short day
plant like chrysanthemum with a critical night lenght = 9.5 hours
You want to prevent
flowering but you have a 9 hour day and 15 hour night
Option 1: turn lights on at
dusk and light the plants for 6 hours = 9 hours night yields vegitative growth
Option 2: Apply 2 hours of
light 4 hours after dark = 9 hours day + 4 hours night + 2 hours
"day" + 9 hours night.
--no one night
period exceeds the critical night length
The required light intensity to get a plant response is very low
minimum for photosynthesis
is 3-4 watts/square meter
Minimum for photoperiod
contron is 0.02-0.09 watts per square meter
The light from one street
lamp can screw you up!
For a 4 foot wide bench
One string of 60 watt
bulbs, 4 feet apart
Not more than 5 feet above the soil level
Run down the middle of the
bench
Two benches can be lighted by
1 string of 100 watt bulbs
6 feet apart
Flash lighting or cyclic lighting
As little as 1 second of light at 0.2 to 0.4 watts per square meter
Flash every 5 seconds
Will prevent flowering
This requires special switches!
The second type of photoperiod control = long night treatment
If you want to initiate flower buds in chrysanthemums in mid summer
Nights are too short
Critical night length of 9.5 hours is not exceeded
Use a black cloth pulled over bench
For every forgotten day when you didn't do the black cloth = 1 day delay in flowering
Can also put in closet (cover cracks to assure it is truly dark)
Gasses
What are the components of unpolluted air?
· Nitrogen (N2) 78.09%
· Oxygen (O2) 20.94%
· Argon 0.93%
· Carbon dioxide (CO2) 0.038% (380 parts per million-ppm)
· Misc 0.01%
·
Moisture 1-3% by volume
CO2 is the third most abundant gas in the air
· Air around highly industrialized areas may be as high as 500 ppm, due to the combustion of coal, gas and oil
· Global greenhouse effect: CO2 traps heat energy, and as the CO2 levels in the air rise, the global temperature may rise
o This is, as yet, scientific conjecture, with few facts to back it up. Though there is a warming trend, it may be that the warming trend is just a continuation of that trend which began during the last ice age (and unrelated to changing CO2 levels in the atmosphere.
· CO2 is required for photosynthesis.
· It is one product of respiration
· 300 ppm is adequate for plants
o up to 2,000 ppm will increase photosynthesis
o >5000 ppm is the maximum tolerated by humans (or it causes blood acidity problems)
· Most common CO2 enrichment for greenhouses
o 1000-1200
o vents must be closed or the CO2 will be vented out!
o 2 inch open vent will negate CO2 enrichement because it will all leak out
o Increased CO2 will require
§ change in fertilizer patterns (especially N, P, K) due to faster plant growth
§ change in light levels: may need supplemental light to take full advantage of the CO2
Handouts
· Greenhouse & Nursery businesses in Alaska
· Seedling dates
· Measuring the light (converting photographic readings to foot-candles)
· Critical night length chart
· Unvented Kerosene Heaters--Ok for Greenhouses
· CO2 levels in an unvented, unenriched greenhouse; CO2 vs light vs photosynthetic rate
The
current copyright laws protect this page, even though not specifically
copyrighted.
However
if you want to use portions of it feel free to do so, though I would appreciate
it if you would acknowledge my authorship.