1. The Physics of Light

2. The Energy for Life
Radiant energy from the sun powers all life on earth
The amount of radiant energy that reaches the earth from the sun each day is the equivalent of about 1 million Hiroshima-sized atomic bombs (that’s a lot)
One third of this energy is radiated back into space
Most of the remainder is absorbed by the earth and converted to heat
Less than 1% is captured and utilized by the process of photosynthesis to provide the energy that is needed for all the activities of life on earth

3. Photons Units of light energy
Familiarly known as “rays” or “waves” of electrons from the sun
When photons are absorbed they boost electrons of the absorbing atom to a higher energy level
A photon of light - produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit
During the fall from high-energy to normal-energy the electron emits a photon – a packet of energy – w/ very specific characteristics  the photon has a frequency, or color that exactly matches the distance the electron falls

4. Energy Content of Photons
The amt of energy is inversely related to the wavelength of light The shorter the wavelength, the greater the energy of each photon in light
Short wave-length light is photons of higher energy
Seen as violet
Long wave-length light is photons of lower energy
Seen as red

5. Electromagnetic Spectrum
The types of electromagnetic radiation are:
radio
infrared
visible light
ultraviolet
X rays
Gamma rays
Electromagnetic energy travels in rhythmic waves – like those created by dropping a pebble into a puddle of water

8. Light Terminology
Wavelength = which is the distance btwn any 2 corresponding points on successive waves – peak to peak or trough to trough
Frequency = the number of waves that pass a point in a space during any time interval – usually in one second
Measured in units of cycles (waves) per second or Hertz (Hz)

9. http://geography. uoregon

10. Ultraviolet Light Sunlight contains abundant U.V. light
Ultraviolet light has a shorter wavelength than visible light and therefore has higher energy
UV waves are invisible to the human eye, some insects, like bumblebees, can see them
It was an important source of energy in the primitive earth
Ozone now shields much of the U.V. light
It’s UV light that causes sunburns!

11. Absorption Spectrum
A specific atom or molecule can absorb only certain photons of light
It depends on the electron energy levels available in the atom or molecule

12. Capturing Light Energy in Chemical Bonds
CAROTENOIDS
Carbon rings
Absorb photons over a wide range of energies
Not highly efficient
Examples are beta-carotene, vitamin A, and retinal
CHLOROPHYLLS
Porphyrin rings
Photons absorbed by chlorophyll excite electrons of magnesium atoms
Two types:
Chlorophyll a - absorbs in the violet-blue range (red is seen)
Chlorophyll b - absorbs in the red range (violet-blue is seen)