Light as a wave Light travels in waves and its energy can be measured in wavelengths. Short wavelengths are high energy Long wavelengths are low energy
Visible Light Spectrum White light or visible light is a blend of all visible wavelengths This range is from 400 to about 800nm 1nanometer is 1 billionth of a meter!
When Light Interacts with matter 1. Light passes through the matter (transparent) 2. Light is reflected (resulting in the colors you see) 3. Light is absorbed (energy is released as heat or used to excite electrons to make chemical bonds!)
Light as a particle Although light travels in waves, it also behaves as a particle. Light particles are called photons. Photons traveling in short wavelengths have high energy. Photons traveling in long wavelengths have low energy. When photons hit atoms, they can excite the atom’s electrons or move them into a higher energy state (Einstein –Photoelectric effect) These high energy electrons can then form chemical bonds
Einstein and the Photoelectric Effect Albert Einstein won the Nobel Prize for his work on the Photoelectric effect which showed that light can behave as a particle called a photon. These photons can excite electrons to higher energy levels allowing them to form chemical bonds to make, let’s say, GLUCOSE!
Photosynthetic Pigments A pigment is a substance that absorbs particular wavelengths of light. The colors that you see are the wavelengths that are reflected, not absorbed. If chlorophyll is a green pigment, then what wavelength is not being absorbed? GREEN
Photosynthetic Pigments Chlorophyll: Two kinds – Chlorophyll A and Chlorophyll B. -Both Chlorophyll A and B absorb red and blue wavelengths and reflect green -Chlorophyll A is the primary photosynthetic pigment – directly involved in converting sun energy into chemical energy -Chlorophyll B and other pigments absorb light energy and transfer the energy to chlorophyll A.
Other Photosynthetic Pigments Carotenes: reflect orange wavelengths Xanthophylls: reflect yellow wavelengths These two pigments allow plants to use a wider range of wavelengths than chlorophyll alone. They are also what gives fall leaves their various colors after the plant shuts down chlorophyll production
Absorption Spectrum for Plant Pigments Absorption spectrum: wavelengths absorbed by a pigment