Methods for Sealing Light Bulbs

1. Pinch Sealing (Press Sealing)

Process: Pinch sealing involves heating the glass tube or bulb envelope and pinching it together around the filament wires or electrodes to create an airtight seal. This method is widely used in incandescent and certain fluorescent bulbs.

Advantages:

Provides a robust and durable seal.

Maintains the vacuum or desired gas composition inside the bulb.

Applications: Incandescent bulbs, compact fluorescent lamps (CFLs), and some halogen lamps rely on pinch sealing for effective operation.

2. Fusion Sealing

Process: Fusion sealing heats the edges of the glass until they melt and fuse together. This seamless sealing process is common in high-intensity discharge (HID) lamps and certain halogen bulbs.

Advantages:

Produces a strong, leak-proof seal.

Ideal for maintaining precise internal atmospheres such as high-vacuum or gas-filled environments.

Applications: HID lamps and quartz halogen bulbs often utilize fusion sealing.

3. Exhaust Tubing Sealing

Process: In this method, an exhaust tube is used to evacuate air from the bulb or introduce the desired gas. Afterward, the tube is heated and sealed, closing the bulb system.

Advantages:

Ensures the bulb’s internal environment remains stable and uncontaminated.

Applications: Commonly used across various bulb types, including incandescent, fluorescent, and HID lamps.

4. Metal-to-Glass Sealing

Process: This technique is used when electrical components, such as tungsten wires or electrodes, need to pass through the glass. A specialized glass with a thermal expansion coefficient matching the metal’s properties is fused to the metal, creating a leak-proof and durable connection.

Advantages:

Prevents gas leakage while allowing electrical connections to pass through the glass.

Applications: Halogen lamps, neon lamps, and certain HID lamps benefit from this sealing method.

5. Adhesive or Epoxy Sealing

Process: Adhesives or epoxies are applied to seal components, especially in LED and specialty lamps. This method is typically used for non-glass materials or hybrid designs.

Advantages:

Offers flexibility and simplifies the manufacturing process.

Applications: Frequently used in LED lamps and decorative bulbs.

6. Flame Sealing

Process: The glass mouth of the bulb is melted by a high temperature flame, causing it to close naturally. An oxygen-gas flame (such as an oxygen-acetylene flame) is usually used to achieve the required high temperature.

Steps

First, evacuate the inside of the bulb or fill it with an inert gas (such as argon).

Then, point the glass tube of the bulb towards the flame and rotate the bulb evenly so that the glass tube is heated evenly.

When the glass softens, use gravity or slight mechanical pressure to close the tube.

Advantages: Cost-effective and straightforward for certain applications.

Applications: Commonly used in Infrared Heat Lamp and basic Reptile Lamp bulbs.

7. Hermetic Sealing

Process: Hermetic sealing creates an airtight seal, often using a combination of metal and glass. Advanced sealing techniques are employed to ensure no gas exchange occurs between the bulb’s interior and the external environment.

Advantages:

Maintains precise environmental stability.

Suitable for high-performance or sensitive applications.

Applications: Used in laser lamps, high-precision scientific bulbs, and aerospace lighting systems.

Methods of Lamp Exhaust

Principle

Use a vacuum pump to extract the air inside the bulb to form a vacuum environment.

A vacuum environment can reduce oxidation and evaporation of the filament, thereby extending the life of the bulb.

Steps

Connect the exhaust pipe of the bulb to the vacuum pump.

Start the vacuum pump and gradually extract the air inside the bulb until the required vacuum degree is reached.

For some high-demand bulbs (such as fluorescent lamps), a vacuum degree of 10⁻⁴ Pa or even lower may be required.

Mechanical Pumping:

Uses vacuum pumps to remove air and impurities from the lamp.

Common pumps include rotary vane pumps, diffusion pumps, or turbomolecular pumps.

Thermal Evacuation:

Heat is applied to the lamp components to outgas materials (e.g., releasing absorbed gases from the filament or glass surfaces).

Often combined with vacuum pumping.

Cryogenic Pumping:

Low temperatures are used to freeze or condense residual gases, improving the vacuum quality.

Suitable for achieving ultra-high vacuum levels.

Gettering:

Involves introducing a getter material (like barium or zirconium) inside the lamp.

The getter reacts chemically with residual gases, capturing them to maintain the vacuum or the gas purity.

Backfilling with Inert Gases:

After creating a vacuum, the lamp may be filled with a specific gas or gas mixture (e.g., argon, nitrogen, or krypton).

This is common for fluorescent lamps, LED lamps, or incandescent bulbs.

Steps of Lamp Exhaust

Preparation:

Place the lamp components (glass envelope, filament, electrodes, etc.) together.

Attach the lamp to the exhaust system via a glass tube or exhaust tip.

Initial Pumping:

Connect the lamp to the vacuum pump.

Begin the evacuation process to remove the bulk of the air from the lamp.

Heating:

Heat the lamp to outgas the materials (filament, electrodes, glass).

Heating is usually performed using induction coils or external heating devices.

High Vacuum Evacuation:

Continue pumping to achieve a higher level of vacuum.

Additional methods like diffusion or cryogenic pumping may be employed for ultra-high vacuum requirements.

Gas Backfilling (if required):

Inject the desired gas or gas mixture into the lamp at a controlled pressure.

This step is critical for lamps like fluorescent or discharge lamps.

Getter Activation:

Activate the getter by heating or other methods to remove residual gases.

This step enhances the vacuum and extends the lamp’s operational life.

Sealing:

Seal the exhaust tube using heat (e.g., torch or flame).

Ensure the lamp is airtight and properly closed to maintain the vacuum or gas fill.

Testing:

Test the lamp for leaks, performance, and operational integrity.

Adjustments are made if any issues are detected.

Key Considerations

Material Outgassing: Ensure all materials are adequately treated to minimize outgassing.

Vacuum Quality: Higher quality vacuums improve lamp efficiency and lifespan.

Gas Purity: The gases used for filling must be of high purity to avoid contamination.

Sealing Integrity: Proper sealing prevents leaks and maintains the desired internal environment.