Lecture 4: Light Flashcards

1
Q

Planck’s Equation

A

e=hc/λ h is Planck’s constant, (6.63 x 10-34 J/s and λ is the wavelength of the photon (nm, 10-9m). Radiant energy is transported by photons which behave both as particles and waves and travels at the speed of light (c = 3 x 1010 m/s in vacuum). The photon energy of the radiation (e) in inversely related to the wavelength of the radiation, as described by Planck’s equation.

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2
Q

Variation in Light Intensity, Duration, and Directionality (Slide)

A

Units - Light is transported in discrete bundles called PHOTONS -Mole of Photons (6.02x1023) = 1 Einstein (E) -Einsteins are only used for PAR (400-740 nm) -The intensity of PAR is determined by the photon flux density, which is about 1500μE m-2 sec-1 near midday on a clear day

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3
Q

Lambert’s Cosine Law

A

Light intensity (LI) at the ground is influenced by its angle of incidence, which depends on the relative height of the sun above the horizon

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4
Q

Lambert’s Cosine Law

A

Light intensity (LI) at the ground is influenced by its angle of incidence, which depends on the relative height of the sun above the horizon

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5
Q

Lambert’s Cosine Law Equation

A
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6
Q

Lambert’s Cosine Law Diagram

A
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7
Q

Light Intensity Varies With…

A

Latitude

Season

Time of Day

Aspect

Slope

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8
Q

Albedo

A

Percent of incident solar radiation that is reflected from a surface

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9
Q

Leaf Area Index

A

Total leaf area per unit of ground area

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10
Q

Leaf Area Index (LAI) Equation

A

LAI= Total Lead Area/ projected ground area

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11
Q

Beer’s Law

A

Describes the relationship between leaf area index (L) and available light

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12
Q

Beer’s Law Equation

A

I=I0e-kLi

I= Available light at any height

e= base of natural logarithm (2.718)

Li= cumulative LAI above height i

k= Light extinction coefficient (measure of degree to which leaves absorb and reflect light)

Higher LAI and higher k → less available light

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13
Q

Euphotic Zone

A

Water depth where light intensity is above the compensation point (high enough to support photosynthetic organisms).

Compensation point is at the bottom of the Euphotic Zone

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14
Q

Light Response Curve

A
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15
Q

Compensation Point

A
  • Light intensity at which gross carbon fixation via photosynthesis is balanced by CO2 -C losses via respiration
  • Explains why it is more difficult for leaves and plants to survive and grow in the subcanopy
  • At the compensation point, a plant is neither losing or gaining carbon (net)
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16
Q

Saturation Point

A
  • Saturation point = light intensity beyond which there is no increase in net C fixation
  • At some point, plants are “saturated” with respect to light intensity
    • Because of inherent limitations of biochemistry
    • CO2 may become limiting (diffusion of CO2 through stomates can’t keep up with photosynthesis
    • Stomates may close if water stress accompanies high light intensity
17
Q

Another Light Response Curve

A