Dr. Suman Paul
Rishi Bankim Chandra Evening College, Naihati, India
Imagine our world without light. Just put off your eyes and think. It seems to be complete dark in real sense. Thus, our common day practices are not at all manageable without the sources of light (electric bulb). Thomas Alva Edison (1847–1931) is being accepted widely as the inventor of first electric bulb.
He developed many devices that greatly influenced life around the world. Among various significant inventions, here our focus will be on electric bulb. Before Edison, many inventors devised incandescent lamps. Main drawbacks of these early bulbs are:
• extremely short life span
• high expense to produce
• high electric current
• difficult to apply on a large scale
Edison started working to tackle these problems and finally managed to develop first commercially practical incandescent lamp with carbon filaments.
Incandescent Light Bulb
Carbon Filament Type
It is an electric light with wire filament heated to a high temperature by an electric current passing through it, until it glows to emit light. The hot filament is protected from oxidation with generally a glass bulb filled with inert gas. It is supplied with electrical current by feed-through terminals or wires embedded in the glass. These are manufactured in a wide range of sizes, light output, and voltage ratings and work well on either A.C. or D.C. As a result, these are widely used in household and commercial lighting.
But those have also few drawbacks. These lamps convert less than 5% of the energy they use into visible light with the remaining energy being converted into heat. The luminous efficacy of a typical incandescent lamp is ~ 15 lm W-1.
Tungsten Filament Type
Next, tungsten filament lamps that lasted longer and gave brighter light than the carbon filament were developed. Filling a lamp with inert gas instead of a vacuum results in twice the luminous efficacy and reduces bulb blackening. So, Argon (Ar) and Krypton (Kr) are used to fill the bulbs. Later, in order to increase the luminosity, silica painted bulbs came into the market.
Fluorescent Lamp (Tube Light)
It is a low pressure mercury-vapour gas-discharge lamp that uses fluorescence to produce visible light. Electric current in the gas excites Hg-vapour which produces short-wave UV light that then causes a phosphor coating on the inside of the tube to glow. Luminous efficacy of this lamp is ~ 100 lm W-1. These are more costly because these require a ballast to regulate the current through the lamp, but the lower energy cost typically offsets the higher initial cost. Compact fluorescent lamps are now available in the same popular sizes as incandescent and are used as an energy-saving alternative in homes.
Compact Fluorescent Lamp (CFL)
CFL uses a tube which is curved or folded to fit into the space of an incandescent bulb, and compact electronic ballast in the base of the lamp. Principle of operation remains the same as in other fluorescent light. Improved phosphor formulations have improved the perceived color of the light emitted by CFLs. Compared to incandescent lamps giving the same amount of visible light, CFLs use 1/5th to 1/3rd the electric power. Only drawback is, CFLs and also tube lights, contains toxic mercury which complicates their disposal after the life time span. Now, for high-efficiency house lighting, white LED lamps compete with CFLs.
Light Emitting Diode (LED)
Lamp An LED lamp is assembling of many LEDs for use in lighting fixtures. The light output of single LED
is less than that of incandescent and CFLs; that is why, multiple LEDs are used to form a lamp. LEDs come into full brightness without having a warm-up time. Electrical efficiency of LED lamps is several times better than incandescent lamps, and significantly better than most fluorescent lamps; Some LED chips are able to emit more than 100 lm W-1 light. LED chips need controlled D.C. electrical power to operate. An appropriate rectifier circuit is required to convert A.C. from the supply to the regulated low voltage D.C. As LEDs are adversely affected by high temperature, those typically include heat sinks and cooling fins. These are the only drawbacks. Most LEDs do not emit light in all directions, and this characteristic affects the design of lamps. Now-a-days, omni-directional lamps are becoming available.
Various parameters for the different kinds of lamps are given and bar diagram for the Luminous Efficacy parameter are shown from which it is easy for all to understand that LED lamps are to be used for home and all other general purpose uses. Thus, with the advancement of scientific research and technology, incandescent lamps are gradually being replaced by other types of electric lamps, such as fluorescent lamps, CFLs, and LED lamps. Because fluorescent lamps and CFLs contain mercury, many fluorescent lamps are classified as hazardous waste. The United States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal. European Union, China, Canada and United States, are in the process of phasing while Colombia, Mexico, Cuba, Argentina, Brazil or Australia, have prohibited them already. But, we surprisingly are using those in full strength. Hope in near future we will also be able to use the light sources which are environment friendly.
Source: bulbs.com, wikipedia.org