Hi everyone! In today’s lesson, we’ll be learning about High Pressure Mercury Vapor Lamps, a type of gas discharge lamp commonly used in industrial and outdoor settings.

1. What Is a High Pressure Mercury Vapor Lamp?

A high pressure mercury vapor lamp is a type of discharge lamp that uses mercury gas at high pressure to produce light. It was one of the first types of high-intensity discharge (HID) lamps developed, and is still used in some public, industrial, and commercial settings.

2. How Does It Work?

Let’s talk about how it works:

• Inside the lamp, there's an arc tube made of quartz or ceramic.

• This arc tube contains mercury and an inert gas, such as argon.

• When electricity is applied, an arc forms between two electrodes.

• The heat from the arc vaporizes the mercury.

• As the mercury vaporizes, it emits light in the ultraviolet (UV) and visible spectrum.

• A phosphor coating (in some types) converts UV light into visible light.

Unlike incandescent bulbs, this lamp doesn’t rely on a glowing filament but on a glowing plasma arc inside the tube.

3. Characteristics of Mercury Vapor Lamps

Here are some key characteristics:

• Bright white or bluish light

• Long lifespan (up to 24,000 hours)

• Takes a few minutes to warm up and reach full brightness

• Requires a ballast to regulate current and help start the arc

• Good for large open areas

4. Advantages

• Long life and low maintenance

• Higher light output than incandescent lamps

• Durable and can be used in harsh environments

• Cost-effective for lighting large outdoor spaces

5. Disadvantages

• Poor color rendering (some objects may look unnatural)

• Contains toxic mercury, so must be disposed of properly

• Slow warm-up time

• Less efficient than modern HID or LED lamps

• Produces UV radiation (needs proper shielding)

6. Common Applications

Mercury vapor lamps are commonly used in:

• Street lighting

• Stadiums and sports fields

• Industrial areas

• Parking lots

• Outdoor security lighting

7. Quick Review Questions

Let’s check your understanding with a few quick questions:

• What gas is used in a mercury vapor lamp?

• What kind of starter does the lamp need? 

• Why is it important to handle these lamps carefully? 

Ans: Mercury, A ballast, Because they contain mercury

Conclusion

To summarize, high pressure mercury vapor lamps are powerful lighting tools with a long history in outdoor and industrial use. But due to safety concerns and energy efficiency issues, many are now being replaced with better alternatives like LEDs.

In our next lesson, we’ll look at another HID lamp — the metal halide lamp — and compare it to mercury vapor lamps.