The use of tungsten wire (tungsten filament) in light bulbs is based on its unique physical properties — namely its high melting point, low vapor pressure, and high electrical resistivity. These characteristics make tungsten an ideal material for producing stable and efficient incandescent light.
- High Melting Point
The melting point is the temperature at which a pure substance transitions between solid and liquid states under a given pressure.
Tungsten has an exceptionally high melting point of about 3,400 °C, the highest among all metals.
Since the operating temperature of an incandescent filament reaches around 2,500 °C, tungsten can easily withstand this extreme heat without melting or deforming.
This thermal stability is a key reason tungsten is preferred for lamp filaments.
- Low Volatility (Slow Evaporation Rate)
Volatility refers to the tendency of a material to evaporate below its boiling point.
Tungsten’s vapor pressure is extremely low, meaning it evaporates very slowly even at high temperatures.
This allows the filament to maintain its shape and mass over time.
As the bulb cools after use, any minimal tungsten vapor tends to recondense onto the filament or the inner bulb surface, helping to prolong filament life and maintain brightness.
- High Electrical Resistivity
Electrical resistivity is a physical property that indicates how strongly a material opposes the flow of electric current.
Tungsten’s relatively high resistivity means it efficiently converts electrical energy into heat, allowing it to reach incandescence (white-hot glow) without requiring excessive current.
This property enables the tungsten filament to produce bright light while maintaining a stable structure.
- Durability and Longevity
Beyond its physical properties, tungsten is also mechanically strong and durable, especially at elevated temperatures.
It does not soften or sag easily under its own weight when heated, unlike many other metals.
This makes it ideal for long-term operation in incandescent bulbs, where the filament must endure repeated thermal cycling without breaking.
- Summary
Tungsten is chosen for light bulb filaments because it offers:
The highest melting point of all metals (≈ 3,400 °C),
Low vapor pressure, minimizing evaporation and filament thinning,
High electrical resistivity, enabling efficient heat-to-light conversion, and
Exceptional durability under thermal stress.
These combined properties make tungsten the most suitable and reliable filament material, capable of glowing brightly under high temperatures for extended periods without melting or breaking — something few other metals can achieve.