Reading Passage 1
Shedding light on it
There are three main types of light bulb for lighting a room: incandescent, fluorescent and, more recently, the light emitting diode (LED) bulb. All three bulbs have their advantages and disadvantages when it comes to purchase price, running costs and environmental impact.
The traditional incandescent bulb has been in use for more than 100 years. It is made by suspending a fine coil of tungsten wire between two electrodes. When a current flows through the wire it reaches a temperature of more than 2,000°C and glows white hot. The bulb is filled with argon, an inert gas, to prevent the wire from evaporating. Traditional light bulbs are not very efficient, converting less than 10% of the energy into light with the rest as heat, making them too hot to handle. Most household light bulbs are rated at 40, 60 or 100 Watts.
Mass production of fluorescent lights began in the 1940s. The standard size is 1.2 m in length and 2.5 cm in diameter. The tube contains a small amount of mercury and the inside surface of the glass has a phosphor coating. There are two electrodes, one at each end of the tube, but there is no wire in between. Instead, mercury atoms absorb the electrical energy and emit ultraviolet (UV); this light is invisible until it hits the phosphor coating on the glass, which emits a visible white light. Fluorescent lights are about five times more efficient than incandescent light bulbs. A 20 Watt fluorescent tube will produce a similar amount of light to a 100 Watt bulb and runs much cooler, which helps to give it 10 times the life expectancy of a bulb.
The bright light produced by standard fluorescent lights makes them an ideal choice for offices and factories, rather than homes, where the incandescent bulb has traditionally reigned supreme. However, the newer compact fluorescent lamps (CFLs) look likely to make the old bulbs extinct. Global warming is the main reason. Compared with an incandescent bulb, a single energy-saving fluorescent lamp will save about one tonne of carbon-dioxide emissions over its lifetime, as well as reduce the consumer’s electricity costs.
Not everybody likes the new CFLs, which have the following disadvantages: they are ten times the price of the traditional bulbs; flickering can occur with dimmer switches; they need to warm up to give full brightness; and they emit a bluish, less natural light that can strain the eye. Traditional bulbs are safer to dispose of because they are free from mercury, which is a neurotoxin. The mercury is safe inside a sealed CFL but it is released into the atmosphere if the bulb is broken. Mercury can accumulate in the body to attack the brain and central nervous system.
The reduced carbon footprint of CFLs in comparison with traditional bulbs may have been overstated. Whilst it is true that traditional bulbs convert 90% of the electricity into heat instead of light, this heat is not wasted. The bulb helps to keep the house warm so less fuel is burnt; for example, less gas or oil. If you change all your bulbs to CFLs it could prove very expensive in the short term and save less energy than you might imagine if your home is properly insulated or you live in a cold climate. If you live in a warm climate, then changing to CFLs will reduce your carbon footprint and the cost of your electricity bills, but the savings will be less than you might expect if the daylight hours are long and the nights are short.
CFLs are themselves under threat from the latest generation of light emitting diodes (LEDs). The LED has been in existence since the 1920s but they have only recently been made bright enough for room lighting. The most common applications to date have been traffic lights, solar garden lights and car brake lights; infrared LEDs are used in television remote controls. LEDs are electronic components that emit photons of light when the current is switched on. Lights for the home are made by clustering several LEDs into a single bulb.
Though more expensive than CFLs, LEDs last up to six times longer and are twice as efficient, producing the same amount of light from half the electrical power (half the carbon emissions). Other advantages of LED lighting include: an ‘instant on’, meaning that there is no warm-up time; no problems with frequent on/off switching, which shortens the life of fluorescent lights; no glass to break because the LED is made from a hard transparent plastic; and they are free from
toxic mercury.
