{"id":132872,"date":"2026-09-09T15:23:03","date_gmt":"2026-09-09T15:23:03","guid":{"rendered":"https:\/\/www.seeedstudio.com\/blog\/?p=132872"},"modified":"2026-09-09T15:28:42","modified_gmt":"2026-09-09T15:28:42","slug":"ndir-co2-sensor-how-it-works","status":"publish","type":"post","link":"https:\/\/www.seeedstudio.com\/blog\/2026\/09\/09\/ndir-co2-sensor-how-it-works\/","title":{"rendered":"NDIR CO2 Sensor Explained: How Infrared Gas Sensing Works"},"content":{"rendered":"\n

This article is part of the Weather Sensor Know-How<\/strong> series: practical guides to the technologies behind industrial weather sensors, environmental monitoring, and microclimate applications. See all guides<\/a>.<\/em><\/p>\n\n\n\n

How can a sensor accurately measure carbon dioxide (CO2<\/sub>) in the air accurately without touching or chemically reacting with the gas?<\/p>\n\n\n\n

One of the most widely used technologies is NDIR<\/strong>, short for Nondispersive Infrared<\/em> Sensing<\/a>. Although the name may sound technical, the basic idea is simple: the sensor determines gas concentration by measuring how strongly a gas absorbs infrared light at a specific wavelength.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

(SenseCAP S1000 10-in-1 Weather Sensor Incorporated a NDIR CO2<\/sub> sensor in its compact design)<\/em><\/p>\n\n\n\n

This guide explains how NDIR CO2<\/sub> sensors work, why they are so widely used in environmental monitoring and smart agriculture, and what to consider when deploying them in real-world projects.<\/p>\n\n\n\n

The Basic Principle: A Molecular Light Fingerprint<\/h2>\n\n\n\n

Every gas molecule interacts with light in its own characteristic way. At certain wavelengths, a molecule absorbs infrared radiation more strongly than at others. This unique pattern can be thought of as the molecule\u2019s optical \u201cfingerprint.\u201d<\/p>\n\n\n\n

CO2<\/sub>, for example, strongly absorbs infrared radiation around the 4.26\u03bcm<\/strong> (micrometer<\/strong>) wavelength. When the CO2<\/sub> concentration inside the measurement chamber increases, more infrared energy is absorbed and less light reaches the detector.<\/p>\n\n\n\n

By measuring how much the infrared signal has weakened, the sensor can calculate the concentration of CO2<\/sub> in the sample gas. This relationship is described by the Beer\u2013Lambert law<\/a><\/strong>: the greater the concentration of an absorbing gas, the greater the attenuation of light over a given optical path length.<\/p>\n\n\n\n

How Does an NDIR CO2 Sensor Work?<\/h2>\n\n\n\n

A typical NDIR sensor uses four key components:<\/p>\n\n\n\n

    \n
  1. Infrared light source:<\/strong> Generates infrared radiation across a suitable range. Depending on the design, the source may be a miniature incandescent emitter, an infrared LED, or another optical emitter.<\/li>\n\n\n\n
  2. Gas chamber:<\/strong> Provides a controlled path through which the sample gas passes. The length of this optical path affects the sensor\u2019s measurement range and sensitivity.<\/li>\n\n\n\n
  3. Optical filter:<\/strong> Selects the wavelength associated with the target gas. This is the \u201cnon-dispersive\u201d part of NDIR technology: instead of using a prism or diffraction grating to separate the spectrum, the sensor uses an optical filter to isolate the required wavelength.<\/li>\n\n\n\n
  4. Infrared detector:<\/strong> Measures the intensity of the infrared light that passes through the gas chamber and converts the optical signal into an electrical signal.<\/li>\n<\/ol>\n\n\n\n

    The sensor electronics then process the detector output and convert it into a gas-concentration reading, such as parts per million (ppm) or percent by volume.<\/p>\n\n\n\n

    \"\"<\/a><\/figure>\n\n\n\n

    (SenseCAP S2103 3-in-1 LoRaWAN Sensor <\/a>measuring CO2<\/sub> with NDIR along air temperature and relative humidity, deployed in a rainforest in Liberia for carbon sequestration<\/a>. Photo Credit: One Planet Education Network<\/a>.) <\/em><\/p>\n\n\n\n

    Why Is NDIR Technology So Widely Used?<\/h2>\n\n\n\n

    NDIR sensing offers several important advantages for CO2<\/sub> and other infrared-active gases.<\/p>\n\n\n\n