Vernier Software and Technology
Vernier Software & Technology

PAR Attenuation in Water


The process of photosynthesis involves the use of light energy to convert carbon dioxide and water into sugar, oxygen, and other organic compounds. In aquatic ecosystems, the amount of light that penetrates the water column determines how much energy is available for algae and plants to perform photosynthesis. As light passes through the water column, its intensity decreases, otherwise known as attenuation. Because of light attenuation, as water depth increases, less energy is available for plants to perform photosynthesis.

Light attenuation is affected by many factors including chemical compounds, suspended solids, and even plankton. Nutrient rich (eutrophic) bodies of water tend to have higher attenuation levels than bodies of water that are low in nutrients (oligotrophic). In other words, the clearer the water, the farther the light can penetrate the water column.

The most common way to measure light attenuation and turbidity is to use a Secchi disk. The disk is lowered into the water column until it is no longer visible. While this is an easy way to observe attenuation, it is open to subjective interpretation. To determine the amount of light available for photosynthesis at different depths, a sensor that measures photosynthetically active radiation (PAR), such as the Vernier PAR Sensor is used.


Use a PAR Sensor to measure the amount of photosynthetically active radiation at different depths in a body of water.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Water Quality with Vernier

See other experiments from the lab book.

4Total Solids
5Dissolved Oxygen
6Biochemical Oxygen Demand
10Ammonium Nitrogen
12Total Dissolved Solids
13Calcium and Water Hardness
14Total Water Hardness
15Chloride and Salinity
16Stream Flow
17Physical Profile of a Lake
18PAR Attenuation in Water

Experiment 18 from Water Quality with Vernier Lab Book

<i>Water Quality with Vernier</i> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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