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DeShark · 13-03-2007, 11:07

Hello all. Long time no see. Been at uni in manchester studying... physics. I just felt that the physics being used was sketchy at best. Lack of clear reliable sources meant that confusion is everywhere and I hoped I might be able to clear up the matter somewhat.

I think most people are happy that flourescent bulbs do not produce as much heat (infrared radiation) as their classical cousins. Simply by looking at the two types of bulb (without the aid of a prism/magnifying glass) you can see that the Energy saving bulbs (Compact Flourescent Lamp or CFL for short) emit bluish white light (http://en.wikipedia.org/wiki/Image:CFBulbs.jpg).

Since the human eye can only view light in the visible spectrum (with wavelength from about 350 - 750nm. Your mileage may vary though) any light emitted outside this range is wasted (for viewing purposes by the human eye). Thus, by converting electrical energy into only visible light (rather than infrared as well) the CFLs are more efficient at lighting and thus require less energy per second (power). In this way, 20 Watts of power can produce the same amount of visible light as an equivalent 100 Watt bulb.

Light is composed of discreet packets of energy (quanta) known as photons. Each photon has a set energy which is related directly to its frequency by the equation Energy = hc/wavelength (where h is Planck's Constant and c is the speed of light). A photon of Blue light (wavelength=400nm) therefore has more energy than a photon of red light (wavelength=700nm).

http://www.howstuffworks.com/solar-cell4.htm (stated as a reliable source previously) says that the energy of photons falling on a crystalline silicon solar panel must be 1.1 to 1.4 eV of Energy which corresponds to a wavelength of 885 - 1127nm. As you can see on this image of the electromagnetic spectrum, these wavelengths lie in the infrared end of the spectrum. Any other photons are wasted. Thus the frequency of the light is paramount to the effectiveness of the calculator's solar panel.

Having said all that, I live in university halls and hence have no choice about the light bulbs used in my room. I think it's a CFL covered with some sort of protective cover that blocks out a ton of the light, so I can't comment on whether the things are actually as bright as they say they should be. It's possible that the manufacturers are using theoretical equivalance values which may not be applicable in practise.

I'd also expect the Energy saving bulbs to be far more cost effective. Assuming that we leave both bulbs on for 10,000 hours, we'd need to buy 10 incandescant bulbs and one Energy saving bulb. Taking the price of an incandescant bulb to be 50p and an energy saving bulb to be £3.50 we've saved money already without even considering the electric bill! Taking a cheap price of electricity of 5p per kilowatt hour gives that the energy saving bulb (25W) uses £12.50 and the equivalent incandescant bulb (100W) uses £50 of electricity. Obviously you don't leave the bulbs on all day and all night, but the point is there.

Finally, I find the response of various people to global warming and environmental damage to be quite shocking. Global warming is no fictional device created to make money! It's a fact. Just like people used to deny that smoking is dangerous to your health. Tackling the situation will require radical action. Complaining at being told to replace your lightbulbs to conserve energy, time and money is just daft. Why fight it? Replace your bulbs, save money, save time and save your children's future.

References:
http://www.howstuffworks.com/solar-cell4.htm
http://en.wikipedia.org/wiki/Electromagnetic_spectrum
http://www.est.org.uk/myhome/efficie...g/bulbratings/

13-03-2007, 11:07	#87
DeShark Member Join Date: Dec 2005 Location: Oswaldtwistle Posts: 31 Liked: 0 times Rep Power: 0	Re: New bulbs. Hello all. Long time no see. Been at uni in manchester studying... physics. I just felt that the physics being used was sketchy at best. Lack of clear reliable sources meant that confusion is everywhere and I hoped I might be able to clear up the matter somewhat. I think most people are happy that flourescent bulbs do not produce as much heat (infrared radiation) as their classical cousins. Simply by looking at the two types of bulb (without the aid of a prism/magnifying glass) you can see that the Energy saving bulbs (Compact Flourescent Lamp or CFL for short) emit bluish white light (http://en.wikipedia.org/wiki/Image:CFBulbs.jpg). Since the human eye can only view light in the visible spectrum (with wavelength from about 350 - 750nm. Your mileage may vary though) any light emitted outside this range is wasted (for viewing purposes by the human eye). Thus, by converting electrical energy into only visible light (rather than infrared as well) the CFLs are more efficient at lighting and thus require less energy per second (power). In this way, 20 Watts of power can produce the same amount of visible light as an equivalent 100 Watt bulb. Light is composed of discreet packets of energy (quanta) known as photons. Each photon has a set energy which is related directly to its frequency by the equation Energy = hc/wavelength (where h is Planck's Constant and c is the speed of light). A photon of Blue light (wavelength=400nm) therefore has more energy than a photon of red light (wavelength=700nm). http://www.howstuffworks.com/solar-cell4.htm (stated as a reliable source previously) says that the energy of photons falling on a crystalline silicon solar panel must be 1.1 to 1.4 eV of Energy which corresponds to a wavelength of 885 - 1127nm. As you can see on this image of the electromagnetic spectrum, these wavelengths lie in the infrared end of the spectrum. Any other photons are wasted. Thus the frequency of the light is paramount to the effectiveness of the calculator's solar panel. Having said all that, I live in university halls and hence have no choice about the light bulbs used in my room. I think it's a CFL covered with some sort of protective cover that blocks out a ton of the light, so I can't comment on whether the things are actually as bright as they say they should be. It's possible that the manufacturers are using theoretical equivalance values which may not be applicable in practise. I'd also expect the Energy saving bulbs to be far more cost effective. Assuming that we leave both bulbs on for 10,000 hours, we'd need to buy 10 incandescant bulbs and one Energy saving bulb. Taking the price of an incandescant bulb to be 50p and an energy saving bulb to be £3.50 we've saved money already without even considering the electric bill! Taking a cheap price of electricity of 5p per kilowatt hour gives that the energy saving bulb (25W) uses £12.50 and the equivalent incandescant bulb (100W) uses £50 of electricity. Obviously you don't leave the bulbs on all day and all night, but the point is there. Finally, I find the response of various people to global warming and environmental damage to be quite shocking. Global warming is no fictional device created to make money! It's a fact. Just like people used to deny that smoking is dangerous to your health. Tackling the situation will require radical action. Complaining at being told to replace your lightbulbs to conserve energy, time and money is just daft. Why fight it? Replace your bulbs, save money, save time and save your children's future. References: http://www.howstuffworks.com/solar-cell4.htm http://en.wikipedia.org/wiki/Electromagnetic_spectrum http://www.est.org.uk/myhome/efficie...g/bulbratings/ Last edited by DeShark; 13-03-2007 at 11:12.