Photosynthetically Active Radiation (PAR)
What is photosynthetically active radiation?
Photosynthetically active radiation (PAR) is the part of sunlight that plants use for photosynthesis. This radiation has a wavelength that ranges from 400 to 700 nanometers. This range is similar to visible light. In direct sunlight, PAR goes up as the sun rises, reaching about 45%.
On cloudy days, diffuse radiation can raise the amount of PAR. It can range from 60% to 70%. On average, PAR makes up about 50% of all solar radiation.
Factors influencing PAR
Many things affect photosynthetically active radiation. These include the angle of the sun and weather conditions like clouds and aerosols.
As the sun gets higher in the sky, light travels a shorter distance through the atmosphere. This leads to higher levels of PAR. Clouds and aerosols can block some of the light. This makes PAR less available.
Factors influencing PAR
Many things affect photosynthetically active radiation. These include the angle of the sun and weather conditions like clouds and aerosols.
As the sun gets higher in the sky, light travels a shorter distance through the atmosphere. This leads to higher levels of PAR. Clouds and aerosols can block some of the light. This makes PAR less available.
Light intensity vs PAR
Light intensity shows how much energy hits a certain area. It is measured in Lux. It includes all the visible light wavelengths that the human eye can see. This range is about 380 to 780 nanometers.
Light intensity depends on the strength of the light source. It also depends on how far the source is from the target area. Barriers that block the light can affect intensity too. A light sensor can measure this value.
PAR is different from light intensity. It refers to the spectrum that plants use for photosynthesis. This is measured in μmol/m²/s and falls within the 400–700 nm range.
Energy from photons in this range is ideal for driving photosynthesis. This value is usually measured with PAR sensors.
Light intensity and PAR are related concepts. They work together to help plants grow. They also help with photosynthesis. Low light intensity leads to lower PAR levels. This makes it harder for plants to photosynthesize.
Too much light can harm plants. It can also affect how they make food through photosynthesis.
What does PAR do?
During photosynthesis, plants use PAR. This is the type of sunlight they can use to make energy. PAR helps plants take in the right light they need for healthy photosynthesis.
Its importance goes beyond just absorbing energy. It also affects the health and growth of the plant. Plants improve their ability to capture PAR by changing the color and shape of their pollen.
This helps them take in more light. Also, looking at PAR in plant tissue gives us hints about plant health.
If the PAR spectrum seen in leaves narrows, it often shows bad environmental conditions or stress. This can be due to disease or malnutrition.
Photosynthetically active radiation (PAR) is crucial for how plants grow, develop, and produce. Here is a summary of its effects, how to measure it, and how it is used:
Impact of photosynthetically active radiation on plants:
1. **Effects on Photosynthesis:**
PAR is the main energy source for photosynthesis. If there is not enough availability, the photosynthetic rate goes down. This leads to smaller leaf areas, thinner leaves, and slower growth.
2.**Effects on Morphology:**
The strength and length of PAR greatly affect how plants grow and change shape. Low PAR and long light periods can lead to thin stems, small leaves, and weak branches. High PAR and short light periods often lead to thick stems, large leaves, and strong branches.
3. **Effects on Yield:**
The right levels of PAR improve both yield and plant quality. Providing enough PAR at night or when there are big temperature changes between day and night can boost plant growth and nutrition.
4. **Effects on Metabolism:**
The strength and length of PAR affect biological rhythms. They also affect how plants use materials, make pigments, and carry out other processes.
5. **Influence on Adaptability:**
PAR is essential for plant growth and development. It has a big impact on how plants adjust to different environments.
Ways to measure photosynthetically active radiation:
1. **PAR Sensors:**
PAR sensors use light principles to detect light in certain wavelength ranges. They change this light into electrical signals to measure PAR intensity. These sensors are put in certain places, like fields, greenhouses, or on plant canopies. This makes sure they get all light radiation.
2.**Professional Instruments:**
Portable PAR radiometers give very accurate and stable measurements. They must be set up and adjusted based on the user manuals before being put at measurement points.
3. **Weather Station Data Estimation:**
Weather stations collect data such as total solar radiation and cloud cover. They use special models and methods to measure PAR intensity. Accuracy relies on taking measurements at the right times and places.
Applications of PAR measurement:
1. **Agricultural Research:**
We study how PAR affects photosynthesis and plant growth. This helps us see how different colors of light affect plants. These insights are vital for analyzing vegetation indexes or plant growth across species and growth stages.
2. **Enhancing Growth and Development:**
Monitoring PAR levels in greenhouses helps select the best crops by checking the light conditions. You can also automate greenhouse roller shutters based on PAR levels. This helps manage lighting better.
3. **Supplementary Lighting Management:**
In controlled places like plant factories, PAR measurement helps check and adjust extra lighting systems. It also tracks light data during the growth cycle.
Good lighting helps plants grow better. They need accurate measurements of light spectrum and assessments of light exposure. This is important for scientific studies on how plants respond to light.
Understanding PAR is key to improving agriculture. It helps researchers and growers boost plant health and productivity. They can manage lighting better with accurate measurements and smart plans.
