Light Bulb Elements

The traditional incandescent light bulb, currently being phased out in many countries because it is considered to be energy inefficient, is really nothing but a glass ball containing a thin filament of tungsten, a metal with a high melting point, in an inert gas such as argon. As electricity passes through the tungsten, the metal heats up and glows bright white. The argon gas prevents the tungsten coming into contact with oxygen and burning.

The compact fluorescent lamp, also known as CFL's or energy saving lights, are commonly being used to replace incandescent light bulbs because they are more energy efficient. Any fluorescent lamp is just a gas discharge tube that uses electricity to excite mercury vapour. CFL's contain between 1mg and 5mg mercury per bulb. Now, while this may not sound like much, it has been estimated that if all of the 270 million CFLs sold in the USA on 2007 were sent to landfills, this would represent about 0.13tonnes, or 0.1%, of all US mercury emissions. Mercury is a toxic metal, and, when disposed of in landfills and waste incinerators, can contribute to air and water pollution.

Light-Emitting Diodes (LEDs) are also considered strong candidates to replace energy inefficient incandescent light bulbs. LEDs consist of a semiconductor chip doped with impurities so that current flows easily in one direction but not in the reverse direction. Light is emitted when an electron falls to a lower energy level while traveling along the semiconductor. The colour of light emitted by an LED is determined by the compound the semiconductor is made of, eg, red though to yellow light is achieved using gallium arsenide phosphide, aluminium gallium indium phosphide, or, gallium (III) phosphide. However, LEDs also contain potentially hazardous substances such as lead and arsenic which are linked to several diseases such as cancers, kidney disease, skin rashes and hypertension.
University of California Irvine's Department of Population Health & Disease Prevention scientists have discovered that low-intensity red LEDs contain up to 8 times the legal amount of lead allowed in California as well as significant levels of arsenic, and that white LEDs, while containing the least amount of lead, contain high levels of nickel.

Reference
Seong-Rin Lim, Daniel Kang, Oladele A. Ogunseitan, Julie M. Schoenung. Potential Environmental Impacts of Light-Emitting Diodes (LEDs): Metallic Resources, Toxicity, and Hazardous Waste Classification. Environmental Science & Technology, 2011; 45 (1): 320 DOI: 10.1021/es101052q

Further Reading
Elements and Compounds
Metals and Non-metals
Definitions of a Mole
Ideal Gas Law
Parts per Million Concentration
Greenhouse Effect

Study Questions

1. Locate each of the elements listed below in the Periodic Table. Provide the symbol for each element.
• tungsten
• argon
• oxygen
• mercury
• lead
• arsenic
• nickel
• gallium
• phosphorus
• aluminium
• indium


2. Draw up a table using the headings metal, non-metal, and semi-metal, and place each of the elements above in the relevant column.
3. What does a Chemist mean when they refer to an inert gas?
4. Estimate the volume of an incandescent light bulb.
   • If the light bulb contains argon gas at 0.1kPa pressure, how many moles of argon are present?
   • Convert the moles of argon gas to a mass of argon gas.
5. Assume a compact fluorescent lamp contains 5mg mercury vapour at 0.3% atmospheric pressure and 25^oC.
   • How many moles of mercury does the compact fluorescent lamp contain?
   • Calculate the volume of the compact fluorescent lamp.
   • What is the concentration of mercury vapour in the CFL in parts per million?
6. There are many different ways to produce electricity; coal-fired power stations, power from uranium fission or from hydroelectricity schemes. For each of these types, discuss the impact on greenhouse gas emissions of replacing incandescent light bulbs with CFLs or LEDs.
7. If a person were to drop and break a compact fluorescent lamp at home, describe the steps that should be taken to safely clean up, and dispose of, the mess.