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What is PAR Sensor and its Uses?

Did you know that light of a specific wavelength directly affects plant health, and PAR (Photosynthetically Active Radiation) sensors can detect changes in this light range as low as 1%? That's why we need them in farming! Electronic sensors and control systems are the heart of intelligent agriculture. Data-driven farming leads to better yield, improved efficiency, cost savings, remote monitoring, and predictive analysis.

PAR sensors are vital to precision farming. They detect light conditions and provide helpful insight into the field conditions for the user. However, the use of PAR sensors is not limited to agriculture. They provide valuable insights into underwater discoveries and play a role in space exploration, research, and climate studies.

To fully understand and utilize the capabilities of a PAR sensor, we must grasp its primary uses, setup requirements, and maintenance aspects. The gain in knowledge can help decide whether PAR sensors are effective for a particular setup. In this blog, we will explore these sensors comprehensively, aiming to provide our readers with a sufficient one-stop compilation of all information. Let's begin!

What is a PAR Sensor?

PAR is fundamentally a light sensor. It detects light between 400 and 700nm. Some advanced sensors can also detect total solar radiation (TSI) 350 to 1100nm, depending on the design. It detects light and converts it into a signal that further devices can store or convert into valuable data.

- Design of PAR Sensors

PAR sensors are generally round. The purpose of a circular shape is to allow lights to come inhomogeneously. The casing holds all the subparts together. There are two legs of a PAR sensor that provide the output signal. A single PAR sensor consists of the following main components:

● Diffuser

● Filter

● Photodiode

● Casing

What is PAR Sensor and its Uses? 1

- Working Mechanism of PAR Sensor

These sensors have a photodiode that converts light into an electrical signal. However, the correct selection of materials and precision engineering are required to extract valuable results. Let's dig deeper into the working mechanism and component selection:

● Diffusing Disc

The diffusion disc may look like a simple plastic sheet, but it performs multiple processes with the incoming light to make the output representative of the downwelling irradiance. Measuring the solar radiation falling on a horizontal surface requires careful evaluation.

○ Hemispherical Integration: The design of the diffusing disc should be round to ensure that the sensor captures all the light coming from the upper hemisphere. The sensor should have a broad view angle for accurate results.

○ Cosine Correction: Using Lambert's cosine law, the sensor should provide a proportionate response to the cosine of the angle between the incoming light and the sensor's surface.

What is PAR Sensor and its Uses? 2 

Considering these two factors, manufacturers decide on the design of diffusing discs. Next is material selection. The material of the diffusing disc can be PTFE or Teflon, acrylic, polycarbonate, or spectralon. It should have high transmittance, diffusing characteristics, stability, and durability, as it will work directly in harsh sunlight. Moreover, it should also provide a tight fit to prevent water ingress. Teflon or PTFE is the most popular choice for diffusing discs in PAR sensors.

 

● Visible Bandpass Filter

Now that the diffuser takes in downwelling irradiance precisely, the detector needs to filter out the light that causes photosynthesis in plants. The filter sits just underneath the diffusing disc to process the light further. The average light range is between 380 and 750 nanometers in the visible spectrum. The whole range does not cause photosynthesis in plants. The bandpass filter cutoff wavelength leaves 400 to 700 nanometer range light.

 

These filters are typically UV-IR cut filters. Depending on the quality of the filter, it can accurately cut off a wavelength of light. High-end filters can respond well to incoming photons across all wavelengths between 400 and 700 nm. The whole process defines the spectral response of the PAR sensor.

● Housing

The case must consist of dark material that does not interfere with the incoming visible light and should not distort the incoming photon across wavelengths. A black case will absorb scattering photons that reach it instead of bouncing back light of different wavelengths.

 

● Photodiode

The photodiode needs to have a larger detection spectrum before the filter passes. When placed in light, it should give a solid response within the 400 to 700nm range. The PAR sensor quality depends on the photodiode's clean and amplified signal.

 

Types of PAR Sensors

Different types of PAR sensors have varying uses, designs, working mechanisms, form factors, and mountings. Here, we will discuss the main categories to paint a general picture of types of PAR sensors that our readers can use in their setup based on requirements:

Types Based on Working Mechanism

● Silicon Photodiode Sensor: These are the more common types of PAR sensors. They simply use photosynthesis to generate an electric current proportional to the light that enters the sensor.

● Quantum Sensor: This is a highly accurate and stable version of the photodiode sensor. It measures the number of photons or PPFD.

Types Based on Mounting

● Fixed-Mount Sensor: These are the types with robust build quality. They are generally made from metal frames to ensure durable performance. The mounting mechanism usually fastens on a solid surface in the field.

● Portable Sensor: Sensors can be handheld or probe types that provide values on the go. They are generally self-powered and have a display to indicate values directly without needing any Modbus-RTU.

Uses of PAR Sensors in Different Fields

Now that we know what a PAR sensor is and how it works, we can move towards its application. Each field uses distinct PAR sensors. The response of control systems can be manual, or users can use IoT devices to take care of the plants. Here are the four uses of PAR sensors:

- Smart Farming

PAR sensors are a vital part of intelligent farming technology. Modern farming uses IoT to enhance productivity through monitoring and data collection to manage planting, harvesting, irrigation, pest control, and drainage. Devices like drones, remote sensors, and remote imagining are popular for data collection. The raw data then goes into a machine learning or AI algorithm, providing meaningful, actionable results.

PARs in smart farming provide the presence of light to predict plant growth, manage light conditions, and monitor the environment. Advanced horticulture farming even features LED or Halogen lights to subsidize the absence of light during the day due to cloud cover or rain. Further automation can automatically adjust light angles to specific plants that need them.

- Climate Studies

Studying local weather for an extended period allows decent data collection to forecast climate changes. PAR sensors can detect 1% of light shifts in the atmosphere. They are sensitive to cloud cover and can predict rain. Combining PAR with weather stations can provide an ultimate management system for agriculture or horticulture monitoring and yield enhancement. 

- Research

Analyzing plant growth can include changes in fertilizer, watering patterns, pesticide use, humidity, and temperature. However, other parameters must stay constant for viable results while performing all these activities. PAR sensors can ensure that plants receive the same intensity of photons during all experimental conditions and that the results are highly reliable, similar to deep-water exploration. PARs can provide valuable insights into how creatures and plants survive at such depths.

- Space Exploration

Plants are a lifeline for astronauts on long missions in space. Optimizing the light conditions to keep the plants healthy is vital for everyone's well-being. PARs can ensure good lighting conditions to maximize oxygen production and food supply.

How to Setup PAR Sensors Step-by-Step?

Step 1: Selecting PAR Sensor

Start by selecting a suitable sensor for your application. Quantum PAR sensors are the ideal choice for monitoring crop photosynthesis. Based on the field condition, select the mounting type.

Step 2: Placing PAR Sensor at the Right Location

Place the sensor where you predict there will be lighting issues for plants. Try to avoid obstructions. The location should be representative of a large set of plants. The ideal height for PAR sensor mourning is around the canopy or crop level. Ensure that it has the right orientation, i.e., facing upwards.

Step 3: Connecting the PAR Sensor to Modbus RTU

The output of a PAR sensor can vary depending on the type. Typically, a sensor will output voltage, amperes, or RS485. If you aim to use voltage and ampere as signals, plan the wiring layout and amplifier installation points. The wire from the sensor to the amplifier should be as short as possible.

After the amplifier, you must install an analog-to-digital (ADC) converter, making the output compatible with a Modbus RTU. If the sensor supports RS485 output, it already has a digital output and does not require any ADC. Ensure that the PAR sensors have an adequate power supply.

Step 4: Acquiring and Analyzing Data

Connect Modbus RTU to a data logger or computer system that will record values in photosynthetic photon flux density (PPFD). Use specialized software to generate reports and visualize trends.

Final Words

PAR sensors are the way forward in the world of advanced farming. They lead to data-driven decision-making, providing better control over crop yield and healthiness. These sensors are easy to set up and require minimum effort to understand the installation process. We recommend going for a quantum photosynthetic active radiation sensor. A sensor that can provide digital output is the best, as it does not require an additional installation of analog-to-digital converters. PAR sensors are vital for horticulture and agriculture. Their usage is becoming undeniable in modern farming applications.

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