photodiode

Air Purification

LEDs are used in air purification in the following ways: 1. **UV-C LED Disinfection** : UV-C LEDs emit ultraviolet light in the germicidal range (200 - 280 nm). When air passes through the light field emitted by these LEDs, the UV-C radiation damages the DNA and RNA of bacteria, viruses, and other microorganisms present in the air, inactivating or killing them. For example, in duct-mounted air purifiers in HVAC systems, UV-C LEDs can disinfect the circulating air. 2. **Photo-catalytic Oxidation (PCO) with LEDs** : Some air purifiers use a combination of a catalyst and LED light. LEDs, often in the visible or ultraviolet range, activate the catalyst surface. This creates reactive oxygen species that break down harmful organic compounds and pollutants in the air, converting them into harmless substances. 3. **Indication and Monitoring** : LEDs can also be used as indicators on the air purifier to show its operational status, such as whether it's on, in a high or low power mode, or if the filter needs replacement.

LED air purification works through the following mechanisms: 1. **UV-C Radiation Disinfection**: UV-C LEDs emit short-wavelength ultraviolet light. When air containing microorganisms like bacteria, viruses, and mold spores passes through the UV-C light field, the high-energy photons penetrate the cells of these organisms. This damages their genetic material (DNA and RNA), preventing them from reproducing and causing them to die or become inactive. For instance, in a tabletop air purifier with UV-C LEDs, as the fan draws in the surrounding air, the UV-C light neutralizes the harmful microorganisms present in it. 2. **Photo-catalytic Oxidation (PCO) Process**: In PCO-based air purifiers, a catalyst material, often titanium dioxide (TiO₂), is coated on a surface. Visible or UV LEDs illuminate this catalyst. The energy from the LED light excites the electrons in the catalyst, creating electron-hole pairs. These reactive species react with water and oxygen molecules in the air to form highly reactive oxygen species like hydroxyl radicals and superoxide ions. These reactive oxygen species then oxidize and break down volatile organic compounds (VOCs), odors, and other pollutants into harmless substances like carbon dioxide and water. An example is an in-vehicle air purifier that uses LED-activated PCO to remove odors and VOCs from the cabin air. 3. **Ion Generation**: Some LED-based air purifiers generate negative ions. When LEDs are used in this process, they might power the ion generation mechanism. Negative ions attach to airborne particles such as dust, pollen, and smoke. These charged particles then cluster together and are more easily captured by the filter or are attracted to surfaces like walls and floors, thereby reducing the number of airborne particles and improving air quality.

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