Light Relations

Light Waves

Amplitude
=Intensity
foot-candles
10,000 fc sum/noon
1000 fc winter
100 fc house
Wave Length
= Color


       400           500           600           700 nm Wavelength
UV   purple   blue   green   yellow   red     IR
---------------VISIBLE SPECTRUM---------------

RAINBOW often wrong in ART.

Colors of flowers, fruits, leaves, etc.

White = all colors of rainbow at once

Pigment in object absorbs all but color reflected to us

Green = absorbs purple/blue and yellow/red
...reflects green to our eye


Blue light causes phototropism:




Light also causes changeover in genetic programs:

Etiolated
(Dark)



Photosynthesis: (review)

CO2 + H2Olight
---------->
chlorophyll
CH2O
sugar
+ O2
It is really a complex set of reactions, NOT one step.
Can be divided into two separate reaction systems:

Light-Dependent Reactions:

H2Olight
---------->
chlorophyll
O2 + ATP + NADPH2

Light-Independent Reactions

ATP + NADPH2 + CO2 ---------->CH2O
sugar

Note: Light-Independent Reactions are dependent on the products of the light-dependent reactions...so they only occur in the light!!

What color of light is needed for Photosynthesis?

(Hint: Chlorophyll is green!)

What intensity of light is needed for Photosynthesis?


How long should the lights be on?

Photoperiodism - light duration process

Here are conditions as found in the long-days of summer:

chrysanthemum
poinsettia
lettuce
spinach
One 24-hr Day of a sequence:SDP=LNPLDP=SNP
16 hr Day = LD8 hr Night = SNvegetativeflowering

Here are conditions as found in the short days of fall (or spring):

chrysanthemum
poinsettia
lettuce
spinach
One 24-hr Day of a sequence:SDP=LNPLDP=SNP
8 hr Day = SD16 hr Night = LNfloweringvegetative

Are the plants measuring the length of the day or the length of the night?

Idea: use interruptions to tell!

Interrupting the night...

chrysanthemum
poinsettia
lettuce
spinach
One 24-hr Day of a sequence:SDP=LNPLDP=SNP
8 hr Day = SD8 hr Night = SNLight
10 sec
8 hr Night = SNvegetativeflowering
Compare the results with the fall results above...note that the night interruption has changed the results!

Interrupting the day...

chrysanthemum
poinsettia
lettuce
spinach
One 24-hr Day of a sequence:SDP=LNPLDP=SNP
8 hr Day = SDDark
10 sec
8 hr Day = SD8 hr Night = SNvegetativeflowering
Compare the results with the summer results above...note that the day interruption has not changed the results.

Notice that it is the length of night that is critical!!

What pigments does this? (Hint: wavelength tells!)

Using a red-light interruption:

chrysanthemum
poinsettia
lettuce
spinach
One 24-hr Day of a sequence:SDP=LNPLDP=SNP
8 hr Day = SD8 hr Night = SNRed
10 sec
8 hr Night = SNvegetativeflowering
Note: red light interrupts the night successfully...SDP(LNP) flowering is prevented.

Using far-red light interruption:

chrysanthemum
poinsettia
lettuce
spinach
One 24-hr Day of a sequence:SDP=LNPLDP=SNP
8 hr Day = SD8 hr Night = SNFar-red
10 sec
8 hr Night = SNfloweringvegetative
Note: far-red light does not interrupt the night...SDP(LNP) flowering is not prevented.

Interrupting flashes can be a sequence of several:

SDP(LNP)LDP(SNP)
Interrupting sequences ending in REDvegetativeflowering
Interrupting sequences ending in FAR-REDfloweringvegetative

Conclusion: the light-detecting pigment is Phytochrome

Recall: Similar R/FR relationship applies to lettuce seeds!


Photoperiodism Flowering Examples

Chrysanthemum Story with Driveway-What is the solution?

Poinsettia Story inside house-what is solution?

Lettuce Bolting Problem in garden-what is solution?


Non-flowering Examples

Tuberization: SDP (Long Nights Too):

Potato, Jerusalem Artichoke, Dahlia Tubers
Bulb Development: LDP (Short Nights Too):
Onions...need long season to make large bulbs!

Bermuda: forms bulbs when day 11 hours or longer
planted in early spring to grow bulbs in CT
day already longer than 11 hours....bulbs form right away...tiny

planted in fall in TX days short, weather mild, large plant
day gets longer than 11 hours in summer, large bulbs form
Spanish: forms bulbs when day 15-16 hours or longer
planted in early spring to grow bulbs in CT
plant gets large before bulbs begin to grow...large bulbs in CT

night day never gets to 15-16 hours...no bulbs ever in TX


Light Around the House

Shade Lovers:

Inside: Ferns, African Violets, Philodendron, Dieffenbachia
Outside: Ferns, Hosta, Astilbe, Begonia, Impatiens


Artificial Lighting

Duration: 16 hours (use a timer)
Intensity:
Incandescent = hot, red, dry
Fluorescent = incomplete blue, dim
GrowLux = more complete, dim
    (use many tubes, close together)
Metal Halide/Sodium Mercury Vapor: bright, complete, HOT, expensive
    Cops will make a house call (DEA)

 

This page © Ross E. Koning 1994.

 

 

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Send comments and bug reports to Ross Koning at koningre∂gmail⋅com.