[Solved] Compact Fluorescent Lamps

Please try to keep this between 150-200 words.

Chemistry In Context

Compact Fluorescent Lamps

 The efficiency benefits of compact fluorescent lamps (CFLs) compared to traditional incandescent light bulbs are well documented.  Fluorescent lights use significantly less energy and last much longer.   The federal government is pushing to phase out incandescent lighting to save energy and reduce greenhouse gas emissions.   But CFLs cost more and many consumers prefer the light given off by incandescent light bulbs.   In addition, using CFLs as a lighting replacement introduces new risks to the environmental and people.  This assignment is designed to help you understand the role of scientific information and scientific thinking in resolving complicated environmental problems.

 ASSIGNMENT

 1.    Read the case study on the following pages and accompanying sections on “Fluorescent vs. Incandescent Light,” and “Mercury Emission.” Also, visit the websites listed below for some background information about how fluorescent and incandescent lamps work, and the health effect of mercury exposure.

http://www.doh.wa.gov/CommunityandEnvironment/Contaminants/Mercury.aspx

http://home.howstuffworks.com/fluorescent-lamp.htm

http://home.howstuffworks.com/light-bulb.htm

 2.    Respond to the following questions in a one or two paragraph submission (150 – 200 words total). 

 Define Fluorescent.

In your own words, briefly explain how light is generated in incandescent and compact fluorescent lamps.

Compare incandescent and compact fluorescent lamps based on their contribution of mercury into the environment.

Describe the human health risks to mercury exposure.

Identify the information needed to evaluate the best choice between the two lamp types.  Make a decision and argue for it using evidence and reasoning presented in the student case study and resources provided.

Fluorescent vs Incandesent Light

Visible light is just a narrow subset of electromagnetic radiation, falling within a range of wavelengths from about 380 to 740 nanometers (nm).  Ultraviolet (UV) energy is electromagnetic radiation with wavelengths shorter than 380 nm, and infrared energy (which we sense as heat) has wavelengths longer than 740 nm.  Photons with shorter wavelengths have higher energy than photons with longer wavelengths.  In both incandescent and compact fluorescent lamps, light energy is released from atoms when electrons drop from a higher-energy orbital to a lower-energy one.  The wavelength of light emitted is determined by the energy difference between the orbitals.

In an incandescent bulb, electrical current causes atoms in the filament to vibrate more quickly – that is, it heats them up.  This atomic vibration can temporarily boost electrons in the atoms to higher energy levels.  When they fall back down to their original orbital, these electrons release energy.  The wavelength of the energy released depends on the temperature of the atoms, and an element heated to a given temperature will emit energy over a board range of wavelengths.  A tungsten filament heated to 2200°C emits energy in the visible range, but only about 10 – 15% of the total.  The vast majority of the energy is emitted in the infrared range, as heat.

In fluorescent lamps, a stream of electrons passes through an inert gas with small amounts of mercury vapor in it.  When the free electrons collide with the mercury atoms, they push some of the mercury’s electrons to higher orbitals.  These excited electrons then drop back down to their original levels, emitting energy as photons.  The energy released by the mercury electrons is in  the UV range, so it is invisible to us.  To make visible light, fluorescent light tubes are coated on the inside with chemical called phosphors.  These are chemical compounds that absorb the UV photons, and in turn emit energy in the visible range.  The specific wavelengths of light emitted depend on the chemical nature of the phosphors, so fluorescent lamps can be created to give off light with a variety of spectral mixes.  Because much less heat is generated in the operation of a fluorescent lamp, it take significantly less energy to create the same light intensity than it would with an incandescent lamp.