Energy-saving lamps have gained widespread application due to their high efficiency and excellent performance. Because the power and illumination range of a single lamp are relatively small, practical engineering applications often require the use of dozens, even hundreds, of the same type of energy-saving lamps for simultaneous illumination. For buildings requiring 24-hour uninterrupted lighting, such as underground supermarkets, underground parking garages, power distribution rooms, and power equipment rooms, uninterrupted lighting energy-saving devices controlled by pyroelectric infrared detection can save a significant amount of electricity. 1. Working Principle of the Device As is well known, the human body has a constant body temperature, generally within the range of 37℃, and emits infrared radiation with a specific wavelength of about 10µm. Passive infrared detectors work by detecting the infrared radiation emitted by the human body at around 10µm. The main principle is: the infrared radiation emitted by the human body at around 10µm is amplified by a Fresnel filter and focused onto the infrared sensing source. When the element receives infrared radiation from the human body and its temperature changes, it loses its charge balance and releases a charge. After subsequent circuit detection and processing, a detection signal is generated. The pyroelectric infrared detection-controlled uninterrupted lighting energy-saving device is mainly designed for locations where intermittent manned work (short-term inspections, operations, etc.) requires continuous lighting from the perspective of on-site monitoring and safe operation. The device consists of a mains power supply circuit, an autotransformer, a pyroelectric infrared detector, drive actuators, and energy-saving lamps. 1.1 Basic Principle of the Pyroelectric Infrared Detector The principle of the pyroelectric infrared detector is shown in Figure 1. The circuit is based on the CS 9803GP, combined with appropriate components to form the circuit for this application. There are two key components in the pyroelectric infrared detector: one is the pyroelectric infrared sensor (PIR), which converts changes in infrared signals with wavelengths between 8 and 12 μm into electrical signals and suppresses interference signals such as white light in nature; the other is a Fresnel lens. The Fresnel lens has two functions: first, focusing, refracting the pyroelectric infrared signal onto the PIR; second, dividing the detection area into several bright and dark areas, so that moving objects (people) entering the detection area can generate changing pyroelectric infrared signals on the PIR in the form of temperature changes. 1.2 Lighting Control Device The main principle of the single-phase uninterrupted lighting energy-saving device is shown in Figure 2. 220V AC mains power is applied to the step-down autotransformer B via fuse FUI, and B outputs a low voltage. Simultaneously, mains power is applied to the control circuit via fuse FU2, and the indicator LED (green) lights up. At this time, the detector probe PIR is in a preheating state, the control circuit output is high, and the contacts 0-1 of relay K close, allowing mains power to be directly applied to the energy-saving lamp. The lamp receives full voltage to start and enters normal operating mode. After a certain time, the PIR preheating ends. When no one enters the detection area, the detector output is low, relay K releases, and the 0-2 contacts of switch K1 close, resulting in a low voltage (approximately 50-70V) applied to energy-saving lamps 1-n. The lamp operates in a low-brightness state, and the indicator LED (red) goes out. Once someone enters the detection area, the pyroelectric infrared detector is activated, relay K closes, and the 0-1 transition contacts K1 close. The voltage on energy-saving lamps 1-n changes to mains voltage (approximately 220V), and lamps 1-n operate at normal brightness, ensuring adequate illumination in the work area. Simultaneously, the indicator LED (red) illuminates. The pyroelectric infrared detector has a delay circuit to prevent malfunctions caused by K's release when the person is stationary, and to ensure that when the person leaves the work area, the lamps automatically delay for a period of time (which can be set as needed) before entering a low-brightness energy-saving operating state. When automatic brightness control is not required for any reason (such as equipment maintenance), the manual switch S can be closed. At this time, K activates, contacts 0-1 close, and the lamps return to normal illumination. During manufacturing, the relay K (coil voltage 12V) should be selected according to the lamp load, with a current margin of one times the rated current. A high-power application with three-phase power supply is shown in Figure 3. Its working principle is the same as that of a single-phase lighting energy-saving device, except that it uses a three-phase autotransformer to distribute the lamps evenly across three phases, thus balancing the three-phase mains power supply to drive more energy-saving lamps and achieve a larger lighting range. Due to the relatively high overall lamp power, the circuit switching actuator uses an AC contactor with switching contacts (coil voltage 220V). 2. Issues to Note 2.1 Autotransformer The autotransformer is one of the main components of this device. Its capacity should be selected based on the load size (total capacity after lamp voltage reduction operation) and with a certain margin. For single-phase power supply applications, the input voltage is 220V (taking the maximum input voltage by 10%, i.e., 240V), and the output voltage is generally between 50 and 70V (depending on the type of lamp, prior testing is required. Use a voltage regulator to lower the supply voltage of the energy-saving lamp until the voltage at which it can stably emit light is the lowest possible value, leaving a voltage margin of about 10V to prevent the lamp from going out due to low voltage during peak electricity usage). The output current is calculated as: IL (current of a single energy-saving lamp operating at reduced voltage) × N (number of lamps) × 1.2 (considering the margin during lamp startup). This can be custom-made by a professional manufacturer or directly modified using a suitable AC autotransformer. For three-phase applications, the input voltage is 380V (taking the maximum input voltage by +10%, i.e., 418V), and the output phase neutral voltage is generally between 50 and 70V. The output current per phase is Ln × 1.2/3 (for energy-saving lamps evenly distributed across three phases). Other issues are handled similarly to those for single-phase applications and will not be elaborated further. 2.2 Delay Time Adjustment The delay time needs to be adjusted according to the requirements of the work. It can be adjusted by adjusting the 1M potentiometer on the control circuit. For short-duration and low-movement work, such as equipment operation, it can be set to about 5-10 mm; for work requiring longer duration, it can be set to 10-30 minutes or longer. 2.3 Installation and Maintenance 1) Avoid obstructions such as obstacles and machinery within the detection range. 2) Try to make the detection range cross the direction of human movement, not directly facing it. 3) The detector installation position should not create blind spots within the detection range to prevent device malfunction. 4) The detection range should have sufficient margin. Consider that in summer, when the ambient temperature rises to near the same as the human body surface temperature (30-32℃), the detection distance will shorten by more than 1/3, or even fail to detect. 5) Clean the Fresnel lens regularly with a mild detergent. Stains or mold on its concentric surfaces will affect the detection distance and performance. 3. Practical Application Results To verify the practical application effect of the lighting energy-saving system, the lighting in an underground power distribution room equipped with 12 45W energy-saving lamps was replaced with an energy-saving device controlled by pyroelectric infrared detection. After more than a year of use, the energy-saving device has been working normally. The attached table shows a comparison of the energy-saving effects before and after the device's use, demonstrating a significant energy-saving effect (device parameters: single-phase voltage supply; voltage regulating transformer is a single-phase 650V+VA autotransformer, input 240V, output tap 65V; delay time is 10 minutes; relay K is a medium-power type with a contact current of 10A). The pyroelectric infrared detection energy-saving device is a lighting equipment with excellent energy-saving effect. Its application not only greatly reduces the energy consumption of energy-saving lamps over long periods but also relatively extends their lifespan and reduces the workload of routine lighting fixture maintenance. It is a practical lighting energy-saving technology solution with good promotional value.