There are four basic types of lighting:
- Incandescent
- Fluorescent
- High-intensity discharge
- LED
Incandescent Bulbs
Thomas Alva Edison invented the incandescent light bulb with reasonable life. Lewis Latimer has perfected it with the use of carbon filament.
The incandescent bulb consists of a sealed glass bulb with a filament inside. When electricity is passed through the filament, the filament gets hot. Depending on the temperature of the filament, radiation is emitted from the filament.
The filament's temperature is very high, generally over 2,000º C, or 3,600º F. In a "standard" 60-, 75-, or 100-Watt bulb, the filament temperature is roughly 2,550º C, or roughly 4,600º F. At high temperatures like this, the thermal radiation from the filament includes a significant amount of visible light.
This principle of obtaining light from heat is called ‘incandescence.” At this high temperature of 2,000º C, about 5 percent of the electrical energy converts into visible light and the rest of it is emitted as heat or infrared radiation.
How Does a Light Bulb Work? (3:47)
Transcript: How Does a Light Bulb Work? (3:47)
Before the advent of electrical lighting, illuminating space was a serious challenge. The only choices people had were candles or oil lamps, neither of which could provide sufficient brightness for extended periods.
However, things took a historic turn in the 1800s, when Thomas Alva Edison conceived and patented the first incandescent light bulb. This innovative technology revolutionized the way we light our homes and workplaces, and has remained largely unchanged from its original design to this day. Incandescent light bulbs function based on a number of interesting aspects of physics, which we'll explore in this video.
The incandescent bulb is made of two main components—the bulb and the filament. The bulb is typically crafted from glass and filled with a vacuum to extend its lifespan. Should air molecules make their way inside, the bulb's temperature would rapidly increase, leading to the glass shattering due to the heat.
The filament is where light production commences. This filament is a long, coiled conductor of electricity, usually made of tungsten. Additionally, an inert gas like argon can fill the bulb’s interior, which aids in slowing down the decay of the tungsten filament.
As electricity flows through the filament via metal contacts, atoms are stirred up, causing electrons to become excited and jump to higher energy levels by absorbing the current's
energy. Almost instantly, these excited electrons lose their extra energy and revert to their initial energy levels, consequently producing small packets of light energy, also known as photons.
From our perspective, this is seen as the bulb lighting up! It’s important to understand that the illumination process of incandescent light bulbs involves the filament being heated to the point of photon emission, thus burning itself to emit light.
A significant part of the electricity coursing through the bulb is utilized to excite the atoms, leading to heat energy production. However, only a nominal fraction of this energy transforms into light, making the bulb's conversion efficiency quite unimpressive, as a substantial amount of energy is wasted as heat.
Over time, various efficient alternatives to traditional incandescent bulbs have been introduced, such as the halogen bulb, fluorescent bulb, and the Light Emitting Diode (LED) bulb. These lighting options utilize different mechanisms to reduce energy loss via heat, providing more substantial light output per unit of electrical energy input.
Halogen bulbs encase a tungsten filament within a quartz capsule filled with an inert gas and minor traces of halogens, enhancing its life through the "halogen cycle."
Fluorescent bulbs, on the other hand, use the fluorescence principle. They energize mercury vapor with electricity, producing ultraviolet radiation that hits a phosphor coating, radiating light energy. These bulbs are four times more efficient and ten times longer-lasting than incandescent bulbs.
Lastly, there are LED bulbs, which are considered the most energy-efficient modern lighting solution. They work by connecting the positive side of the voltage to the anode (the longer leg of the LED) and the negative side to the cathode (the shorter leg). When a forward voltage is applied, it allows the flow of current through the LED, prompting the release of light.
In an era of dwindling resources, sustainable and energy-efficient lighting equipment like LED bulbs, which emit minimal heat energy and last up to 25,000 hours, are the future of lighting in homes and commercial spaces. As inventors continue striving to create better and more efficient technologies, the future of lighting appears incredibly bright!
Let’s now look at several different types of incandescent bulbs.
Standard incandescent bulbs
Standard incandescent bulbs are most common and yet are the most inefficient. Larger wattage bulbs have a higher efficacy (more lumens per Watt) than smaller wattage bulbs.
Instructions: Click the “graph” button below to create a graph comparing Watts and efficiency, and then answer the question below.
Comparison of Watts and Efficiency for an Incandescent Bulb
The table below compares the number of Watts of a light bulb to its efficiency (lumens per Watt).
| Watts (power) | 25 | 40 | 60 | 75 | 100 | 150 |
|---|---|---|---|---|---|---|
| Efficiency (lumens per Watt) | 8 | 12 | 14 | 15 | 17 | 19 |
Based on this data, it is clear that as the number of Watts increase, so does the efficiency.
Tungsten halogen bulbs
Tungsten halogen is an incandescent lamp with gases from the halogen family sealed inside the bulb and an inner coating that reflects heat back to the filament. It has similar light output to a regular incandescent bulb, but with less power. Halogens in the gas filling reduce the material losses of the filament caused by evaporation and increase the performance of the lamp.
Tubular tungsten-halogen bulbs
Tubular tungsten-halogen bulbs are commonly used in “torchiere” floor lamps, which reflect light off of the ceiling, providing more diffused and suitable general lighting.
Although these provide better energy efficiency than the standard A-type bulb, these lamps consume significant amounts of energy (typically drawing 300 to 600 W) and become very hot (a 300-W tubular tungsten-halogen bulb reaches a temperature of about 2600° C compared to about 600° C for a compact fluorescent bulb). Because Tungsten-halogen lamps operate at very high temperatures (high enough to literally fry eggs), they should not be used in fixtures that have paper- or cellulose-lined sockets.
Halogen bulbs
A halogen bulb is often 10 to 20 percent more efficient than an ordinary incandescent bulb of similar voltage, wattage, and life expectancy. Halogen bulbs may also have two to three times as long a lifetime as ordinary bulbs. How much the lifetime and efficiency are improved depends largely on whether a premium fill gas (usually krypton, sometimes xenon) or argon is used. The image below shows a picture taken with an Infrared camera comparing the heat produced by a halogen and a compact fluorescent light bulb. The red and white color zones are extremely hot, and the blue zones are cooler.
Reflector Lamps
Reflector Lamps - Light waves from a bulb spread in all directions. The light that goes toward the back is not useful when the light is most needed in the front. Reflector lamps (Type R) are designed to spread light over specific areas.
Reflector lamps have silver coating on the sides, like any mirror, and therefore all the light waves passing through the sides or the back are reflected to the front. Therefore, they are called reflector lamps and are also called floodlighting, spotlighting, and down lighting bulbs.
For more information on the history of the light bulb, check out the History of the Light Bulb by the US department of energy.