Currently, China is striving to build a resource-efficient and environmentally friendly society, with the concept of "green lighting" gradually gaining widespread acceptance. With continuous advancements in technology and the rapid development of semiconductor material application techniques, low-power LED light sources have been widely adopted in landscape lighting, while high-power LED streetlights are increasingly drawing attention from various sectors.
The light-emitting principle of LED lamps:
LED (Light Emitting Diode), or light-emitting diode, is made from III-IV group compounds and is a solid-state semiconductor device that can directly convert electricity into light. The core of an LED is a semiconductor wafer, which consists of three parts: one is a P-type semiconductor where holes dominate, and the other end is an N-type semiconductor. When an electric current flows through the wire and acts on the wafer, electrons and holes are pushed into the quantum well. Inside the quantum well, electrons and holes recombine, emitting energy in the form of photons. This is the principle behind LED light emission. The wavelength of light, or its color, is determined by the materials forming the P-N junction.
The luminescence principle of high-pressure sodium lamps:
High-pressure sodium lamps utilize the arc generated between the electrodes at both ends of the arc tube when electrified. The high temperature of the arc causes the sodium amalgam inside the tube to evaporate into mercury vapor and sodium vapor. Electrons emitted by the cathode, while moving toward the anode, collide with the atoms of the discharge material, imparting energy that leads to ionization or excitation. These excited states then return to the ground state, or transition from the ionized state to an excited state before reverting to the ground state in an infinite cycle. During this process, the excess energy is released in the form of light radiation, producing illumination.
High-power LED streetlights are a new lighting method that achieves illumination by powering groups of light-emitting diodes with low-voltage DC, featuring high brightness and excellent color rendering. Additionally, since LED streetlights operate on low-voltage DC, they can be integrated with solar energy, making solar-powered LED streetlights a potential future solution for road lighting.
1. Regarding Energy Efficiency Analysis and Comparison
The lighting installation power of the two should be compared under the premise of achieving the same illuminance (brightness) level and close lighting quality standards. Since high-pressure sodium lamps with high-power tubes (250~400W) have high luminous efficacy, reaching 130~140lm/W, while low-power tubes (100~150W) have an efficacy of approximately 80~100lm/W, and currently used high-power LED streetlights primarily employ 1W LED tubes with similar efficacy, it is advisable to analyze high-power and low-power streetlights separately.
(1) High-power (≥250W) streetlights: High-pressure sodium lamps have high luminous efficacy. Considering three factors—ballast losses, luminaire efficiency, and light distribution utilization—the combined efficacy is estimated at 0.55, resulting in an effective luminous efficacy of approximately 70~75 lm/W for sodium lamps. Currently, the effective luminous efficacy of LED streetlights in the U.S. is around 62 lm/W, while top domestic manufacturers have achieved 56~58 lm/W. Therefore, for high-power streetlights, LED currently exhibits lower energy efficiency compared to sodium lamps.
