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Detailed Explanation of the Technical Requirements for Detecting Light Leakage in Ducts. The detection of light leakage in ducts is a crucial aspect of quality control in the construction of ventilation and air conditioning systems. It is used to verify the integrity of the installed duct systems, ensuring that no air leaks occur due to gaps in seams, joints, or connections during operation, which could otherwise affect the system’s efficiency, stability, and overall performance. This testing method takes advantage of the property of visible light penetrating weak areas in air ducts; under specific lighting and observation conditions, it allows for the visual identification of light leakage points, thereby assessing whether the quality of duct fabrication and installation meets the specified standards. The following provides a comprehensive explanation from aspects such as the purpose of testing, scope of application, basis for formulation, construction preparations, process flow, operating procedures, technical standards, and precautions. I. Purpose and Significance of Testing As a core component of building ventilation, air conditioning, and smoke control systems, the integrity of ductwork is directly related to the efficiency of system operation and energy consumption levels. If there is air leakage in the ductwork, it not only leads to losses of cold and heat energy and increases operating costs, but it can also cause problems such as a decline in indoor air quality and an imbalance in the system’s air flow. Light leakage detection, as a simple, intuitive, and cost-effective method for on-site inspection, enables the timely identification and location of air leakage points prior to system commissioning. This provides a basis for subsequent sealing procedures, helping to avoid rework and operational failures caused by defects in concealed components, and thus ensuring the safe, stable, and efficient operation of the system. II. Scope of Application This testing method is applicable to the inspection of the airtightness of ducts in low-pressure and medium-pressure systems, covering ducts made of various materials such as galvanized steel sheets, stainless steel sheets, and composite materials. It is particularly suitable for quality control at the connection points of the front-end collection pipes, main pipes, and branch pipes. The testing should be completed before the insulation work on the air ducts is carried out, to ensure that the testing process is feasible and the results are accurate. III. Basis for Formulation These technical requirements are formulated in accordance with the relevant provisions of the \"Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering\" (GB50243-2002), and by taking into account practical engineering experience, the testing procedures and acceptance criteria are defined to ensure that testing activities are carried out in an orderly and well-founded manner. IV. Construction Preparation 1. Preparation of testing tools: A safe power supply with a voltage not exceeding 36V (such as 24V or 12V) and a power output of at least 100W is required, along with a safe work light or a light source of equivalent brightness ； At the same time, prepare a traction rope of sufficient length, a ladder, or a mobile scaffold to facilitate the movement and positioning of the light source inside the air duct. Low-voltage light sources are chosen primarily for safety reasons, to prevent the risk of electric shock, while high-power light sources help improve the accuracy and effectiveness of detection. 2. Environmental condition requirements: Testing should be conducted in a dimly lit environment; it is recommended to carry it out at night or in a enclosed space. If the external light is strong, the light source can be placed outside the air duct, and it is possible to check whether there is any light leakage at the seams on the inner wall, thereby reducing missed detections caused by interference from ambient light. V. Process Flow and Operating Procedures: Detection is carried out using either the method of \"light source from within, external observation\" or \"light source from outside, internal observation\". Typically, the light source with a protective cover is placed inside the duct, and moved slowly using a pull rope to inspect the flange joints, seams, rivet points, and other connection areas section by section. During each inspection, the operator should stay at the seam to observe; once any light leakage is detected, it should be marked as a light leak point. For complex systems, it is advisable to adopt a method of segmented detection and comprehensive analysis, focusing on the main pipe and trunk pipe areas. VI. Technical requirements and acceptance criteria: In accordance with GB50243-2002, 1) For low-pressure system ducts: There shall be no more than 2 light leakage points per 10 meters of joint length, and the average number of such points over 100 meters of joint length shall not exceed 16; this meets the acceptance criteria ； 2. Medium-pressure system ducts: It is considered acceptable if there is no more than 1 light leakage point per 10 meters of joint length, and an average of no more than 8 such points per 100 meters of joint length. All detected slit-shaped light leaks or localized light leakage points must be sealed. During sealing, the surface around the area where light is leaking should first be cleaned to ensure there is no dust or oil residue ； Then select an appropriate sealing material, such as sealant or a seal strip. For small gaps, sealant can be used directly to fill them; for larger holes or seams, it may be necessary to press a seal strip in place or reinforce the connections ； During the operation, it is necessary to ensure that the sealing material covers evenly and adheres tightly to avoid bubbles or cracks. After treatment, retesting should be conducted until the standards are met. VII. Precautions and Prevention of Common Quality Issues 1. Safety requirements: A safe voltage of 36V or less must be used to prevent electric shock accidents ； The light source should be equipped with a protective cover to prevent damage or fires. 2. Timing of inspection: It should be completed before the insulation work begins, to prevent leaks from going unnoticed and unable to be repaired due to the insulation layer covering them. 3. Common issues: Excessive ambient light can lead to missed detections; it is recommended to carry out operations at night or in shaded conditions ； Furthermore, operators should receive professional training to be able to detect faint light leaks, thereby avoiding errors resulting from subjective judgment. 4. Other common quality issues and solutions: During testing, light leakage may occur due to the aging of duct materials or improper installation. For such issues, the aged materials should be replaced promptly or the air ducts reinstalled to ensure their airtightness. Additionally, if a large number of light leakage points are found during inspection, the entire section of the ductwork should be thoroughly inspected, and appropriate reinforcement measures should be taken. VIII. Recording and Archiving: The inspection process should be documented accurately in the \"Duct Airtightness (Light Leakage) Inspection Record Form\". This form should include details such as the project name, construction unit, inspection location, inspection length, the number and location of light leakage points, as well as the corrective measures taken and the results of re-inspection. These records serve as important documentation for the quality assessment of the project and are kept for future reference. In summary, duct light leakage detection is a systematic and highly standardized quality control measure. Through scientific organization, standardized operations, and strict adherence to standards, the sealing performance of duct systems can be effectively improved, eliminating problems such as leaks and spills. This helps to create building mechanical and electrical systems that are efficient, energy-saving, safe, and reliable, reflecting the high standards required for meticulous management in modern construction projects.