The legacy filament bulb is commonly known as the tungsten bulb. The element has for over a century proven to be a good choice made by our forefathers. There is none like tungsten in performance. To date, the majority of electrical lighting uses a tungsten bulb. Though the technology is first changing, I don’t foresee the bulb becoming obsolete. More advancement is being made on the bulb that the principle of operation remains the same. Great future the illumination enthusiasts.
The early age and middle age man used primitive sources of light that is firewood. As a technical person, this history may not mean a lot to you. But how does the light come about? Sun is the chief source of light and heat in the universe. Before electricity man used firewood, kerosene, and other petroleum fuels to light up the world. The study of material science will help us understand the reactions that produce forth light.
All sources of light involve chemical reactions that release energy in the form of light. This piece will concentrate on tungsten filament. This is the legacy source of electrical lighting which was invented by Thomas Edison in late 19th century. Tungsten as material was selected as the best among the many that were experimented in the lab. Before we discuss how tungsten bring forth light let us look at the properties.
Properties of tungsten
- It has the highest melting point- it melts at 3422
C
- The high boiling point of about 5930°C.
- Very high density- 19.3g/cm3
- Good conductor of electricity
- Good conductor of heat
- High electrical resistivity- 52.8 nOHMm at 20°C
- Highly ductile- it can be drawn into thin wires.
- How tungsten produces light
All materials at high temperatures produce light. The temperature at which they begin to emit light is different because of their chemical composition. You have noticed charcoal emitting light when it red hot. Carbon was initially used as the filament prior to tungsten. The challenge presented with most materials was as they were heated, they melted and then evaporated and therefore ceased to produce light. It’s important to note that the higher the temperature, the higher the glow. This only means that an element with a high melting point will produce more light without melting. Tungsten the element known to have the highest melting point becomes the best fit giving a large amount of light (when heated at high temperatures) for a long duration of time (without melting).
Being a good conductor of electricity meant it can be heated electrically. Now, electrical heat in a material is proportional to the resistance of a material. The element makes a score as it has high enough resistivity. This means that is a good converter of electrical energy into heat. A tungsten filament converts electrical energy into heat and makes it glow. The bulb emits both light and heat, the heat makes the lit area feel warm.
Light color explained
To understand the emission of light you need some chemistry of atoms background. An atom consists of a nucleus and electrons in discreet energy levels revolving around the nucleus. There is a pattern of electrons array around the nucleus. Electrons in the innermost energy level possess the highest energy and are the most stable. The energy and stability decrease outwards. These electrons seek stability by falling to vacant lower energy levels. Change of energy level means a change in energy possessed, a fall to lower energy level results in the emission of the discreet amount of energy. On the other hand, a rise to a higher energy level involves absorbing a discreet amount of energy. For most materials including tungsten, heat energy raises electrons to higher energy levels and the falling of electrons to lower energy levels emits discrete light energy. The falling of electrons to a lower energy level is an attempt to seek stability and is a natural process. Light of discreet energy called a photon travels at a specific wavelength and frequency. When this light is within a given range of frequency it is visible by the human eye and is referred to as visible light.
When tungsten is heated at different temperatures it produces different colours of light. This is caused by varying energy levels that electrons lose when falling to lower energy level. For low energy loss, red colour is emitted while for high energy emission blue colour is produced. All other colours fall between the ranges. The filament is enveloped by a glass housing filled with inert gas. This reduces the oxidation process of the filament that can make it to burn out.
Advantages
- It produces more light compared to other materials.
- It has warm light- a good fit in cold areas.
- It’s durable
- Low cost compared to other types.
Disadvantages
- Low efficiency- high energy in form of heat.
- It produces heat which may not be required in areas meant to be cold.
- Its lifespan is short compared to LED or fluorescent tubes.
- The filament is fragile- when under stress it easily gets damaged.