Hello, class! Now, we are going to learn about a widely used and very recognizable type of lighting — the High Pressure Sodium Lamp, or SON lamp."

1. What Is a High Pressure Sodium Lamp?

A High Pressure Sodium lamp is a type of HID (High-Intensity Discharge) lamp. It is known for its very high efficiency and distinctive yellow-orange light. SON lamps are often used for street lighting, parking lots, and industrial areas.

2. How Does It Work?

Let’s look at how an SON lamp works:

• Inside the lamp is an arc tube made of ceramic or alumina.

• The arc tube contains a small amount of sodium, mercury, and xenon gas.

• When voltage is applied, the xenon gas helps start the arc between the electrodes.

• As the arc heats up, it vaporizes the sodium and mercury.

• These vapors emit a bright yellow-orange light as electrons excite the sodium atoms.

3. Key Components

• Arc tube – where the light is generated

• Outer bulb – protects the arc tube and contains inert gas

• Electrodes – conduct electricity through the arc tube

• Ballast – regulates current and provides starting voltage

• Ignitor – helps start the arc

4. Advantages of SON Lamps

• Very high luminous efficiency (up to 150 lumens per watt)

• Long lifespan (typically 12,000 to 24,000 hours)

• Low maintenance cost

• Operate well in outdoor and rough environments

• More efficient than mercury vapor and metal halide lamps

5. Disadvantages

• Poor color rendering – objects may appear dull or unnatural

• Takes time to warm up to full brightness

• Contains toxic materials, like sodium and mercury

• Color shift occurs over time

• Require ballasts and ignitors, which can add cost and complexity

6. Common Applications

SON lamps are best used in situations where high brightness and energy efficiency are more important than color accuracy, such as:

• Street lighting

• Tunnel lighting

• Parking garages

• Stadiums and industrial sites

• Outdoor security lighting

7. Quick Review Questions

Let’s test your understanding with a few questions:

1. What gas is used to help start the arc in an SON lamp? 

2. What color of light does an SON lamp produce? 

3. What are SON lamps commonly used for? 
   
   
   Ans: Xenon, Yellow-orange, Street lighting, parking lots, etc.

Conclusion

To summarize, High Pressure Sodium lamps are among the most efficient HID lamps, known for their long life and high light output. However, due to poor color rendering and environmental concerns, they are now being replaced in many places by LED lighting.