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Why is light important?. 1.) Photosynthesis 6CO 2 + 12H 2 O ( chl & light ) C 6 H 12 O 6 + 6O 2 + 6H 2 O 2.) Needed for chlorophyll production 3.) Photomorphogenesis - development of certain plant parts, esp. flower initiation and development, seed germ. Why is light important?.

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why is light important
Why is light important?

1.) Photosynthesis

6CO2+ 12H2O(chl & light) C6H12O6 + 6O2 + 6H2O

2.) Needed for chlorophyllproduction

3.) Photomorphogenesis - development of certain plant parts, esp. flower initiation and development, seed germ...

why is light important2
Why is light important?

4.) Anthocyanin production

5.) Light is energy! Some is converted to heat when it strikes a plant surface

6.) Light influences translocation in the plant

7.) Light can affect abscission (dropping of plant parts) when intensity suddenly changes

light in te ns ity
Lightintensity

-Refers to brightness

-Often the limiting factor for growing or maintaining plants indoors

light measurement
Light measurement

Light can be measured

in many ways!

- Light meter (photoelectric cell)

Footcandle = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 foot

Lux = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 meter

slide8
Conversion:

1 fc = 11.1 lux

These units measure only visible light (what the eye can see!)

For scientific reporting of light quantity, you might hear the following terms:

candela

lumen

photon flux

quanta

joules

sources of light for an interior
Sources of light for an interior

1.) Natural (sunlight)

2.) Artificial (bulbs and tubes)

3.) Combination of the above

sunlight
Sunlight

Factors affecting light penetration into a room:

1.)Windows

-type (glass/plastic/glazing)

-reflection

-barriers (overhangs, screens, curtains, shades, buildings and plants outside, dirt, etc...)

-orientation (N, S, E, W)

sunlight12
Sunlight

2.) Latitude

(distance away from the equator)

24

22

20

Burlington

18

16

Atlanta

14

12

Equator

10

8

6

4

2

J F M A M J J A S O N D J

(calendar year)

sunlight13
Sunlight

3.) Geographic region

-annual cloud cover

-atmospheric pollution

-humidity

-elevation

artificial light
Artificial light

Supplemental to sunlight

-extend hours of light

-increase intensity of light

Sole source

-role: room lighting

plant lighting

combination

artificial light15
Artificial light

Considerations not necessary with sunlight:

spectral emission = range of colors produced by the light

Light Quality!!!

Ultra-

violet

Gamma

rays

Infrared

Radio

X-rays

Visible Light

(nanometers)

y

e

l

l

o

w

i

n

d

e

g

o

v

i

o

l

e

t

o

r

a

n

g

e

b

l

u

e

g

r

e

e

n

r

e

d

380 430 470 500 560 600 650 760

p hotosynthetically a ctive r adiation p a r
Photosynthetically Active Radiation (PAR)

Range =

400 - 700nanometers

Based on length of each wavelength of light

~~~~~~~~~~~~~~~~~~~~

Chlorophyll and associated pigments utilize light energy primarily in the blue(430 nm) and red (670 nm)

choosing artificial lights
Choosing artificial lights

Sources:

Incandescent bulb

Pros:

-small

-no special fixtures

-dramatic

-range of wattages available

Cons:

-light is concentrated

-7% of energy usable light

-90% of energy heat!

-short life (750 hrs.)

-high in red/orange & low blue

slide18
Fluorescent tubes

(cool-white, warm-white, daylight)

Pros:

-diffuse light, new fixtures avail.

-efficient! (7x incandescent!)

-22% of energy usable light

-cool! 36% of energy heat

-last 8,000 - 9,000 hrs

(15x longer than incandescent!)

Cons:

-work best if 70 - 90oF

- traditionalfixtures bulky

-low far-red emission

-contain mercury

-emit ultraviolet light

slide19
Cool

white

Warm

white

slide20
Daylight fluorescent vs. Incandescent bulb

100

90

80

70

60

50

40

30

20

10

0

Fluorescent

Relative energy

Incandescent

400500 600 700

(nanometers)

slide21
Sodium vapor lamps(HID lighting)Pros: -25-35 % of energy visible lightCons: -yellow/orange/red spectral emission only! -large ballast (requires special lighting fixtures)
what happens when light contacts a leaf
Reflected

Absorbed

What happens when light contacts a leaf?

Transmitted

ways to increase artificial light
Ways to increase artificial light:
  • Added white reflectors to fluorescent fixtures
  • Paint surrounding walls white
  • Regularly clean tubes to remove dust
  • Regularly clean plants to remove dust
  • Change tubes regularly
  • Keep plants centered under fluorescent tubes
natural vs artificial light intensities
Natural vs. Artificiallight intensities
  • Noon sun during summer can measure 10,000fc
  • Cloudy winter day: 500-2,000 fc
  • Inside rarely exceeds 1,300fc
    • typical office 20-30 fc
    • typical living room
      • day: 10-1,000 fc
      • night: 5-10 fc
light quantity
-Light quantity-

Total light per day = footcandles of light x hours of light/day

Example:

100 fc x 16 hrs of light/day

1,600 fc hours/day

Sometimes, extending the daylength can compensate for a lower light intensity...

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