Table of Contents
Light and Plant Pigments
The different pigments found in plants are capable of absorbing specific wavelengths of light in the visible spectrum. Wavelengths that are not absorbed are reflected. This is why we see leaves as green. The chlorophyll pigments found in the leaves reflect the green wavelengths back to our eyes. The other wavelengths in the spectrum are absorbed for use in photosynthesis.
Practice: Absorbed and Reflected Wavelengths of Light
Click the image below to open the simulation and explore how we see color.
As you experiment with the different colored bulbs and filters, you will note that the light is only able to pass through filters that are the same color. All other colored filters absorb the light.
Absorption Spectra
A spectrophotometer can be used to create a graph that plots the wavelength of light against the absorption of light. This graph is called an absorption spectrum. The absorption spectrum of chlorophyll a and chlorophyll b shows that they absorb light best at wavelengths in the violet-blue range and red range. Absorbance drops sharply in the green-yellow range, indicating that these wavelengths are reflected.
Light and Plant Health
A sign of plant health is viewed through the near infra-red wavelength of light. While we cannot see this spectrum of light with our eyes, we can use other sensors to detect this light. Compare the black and white image below with the infra-red image. What differences can you see in the two images that will help you understand how this is a useful measure of plant health?
Use this link to view a slider image.
Visible light wavelengths (between 400 nm-700 nm) are strongly absorbed by the pigments in leaves (chlorophylls, xanthophylls, carotenoids). These pigments utilize the energy of these wavelengths to take part in the light reactions. The cellular structure of leaves do not absorb wavelengths longer than these wavelengths (>700 nm in the infra-red range). By comparing the amount of visible light to the amount of near infra-red light that are reflected, one can gauge the relative health of leaves, forests or jungles . This is the rough description of the Normalized Differential Vegetation Index (NDVI) that scientists use in conjunction with satellite imagery to assess the health of vegetation.
Print this page
