light and CDs

[i<3ciencias]

how does light do damage to a cd?

do other types of light besides sunlight cause damage? or is it just sunlight?

[deleted-71591]

Light damages a cd by causing the silver layer within the disc to decay. You can check your cd for such damage by holding it up to a light and looking for visible holes.

Sunlight is the only kind of light that do any real damage to a cd, although exposure to heat or humidity can also cause damage.

[Louise]

Light damages a cd by causing the silver layer within the disc to decay. You can check your cd for such damage by holding it up to a light and looking for visible holes.

Sunlight is the only kind of light that do any real damage to a cd, although exposure to heat or humidity can also cause damage.

This could be the topic of your science fair project- sunlight is "white light" that contains all the colors. What color of the light destroys the CD the fastest? Obviously, some colors cause little to no damage (I say "obviously" because a CD is played with a laser beam (a beam of light)- whatever color this laser is must not damage the cd).

You could look at wikipedia to see how CD technology works.
http://en.wikipedia.org/wiki/Compact_disc


Louise

[i<3ciencias]

Thank you!!! =)

[i<3ciencias]

ok so does any other type of light to damage to a cd, other than visible light, in accordance to the entire electromagnetic spectrum?

[Louise]

ok so does any other type of light to damage to a cd, other than visible light, in accordance to the entire electromagnetic spectrum?

Not all visible light damages CDs- the laser used to read them is red- please see either the wikipedia article I cited early or http://micro.magnet.fsu.edu/primer/java ... index.html

As for the entire electromagnetic spectrum- yes, I would imagine large parts of it would damage cds - but you are only concerned with a small portion of that spectrum- the "visible portion". See:
http://imagine.gsfc.nasa.gov/docs/scien ... ctrum.html
if you are unclear

We are here to help you design and complete your science project- not to do your research for you. Why don't you try to find this out yourself? There are two ways to go about this- first, search for the answer to the question "what colors of light damage cds" and "what colors of light damage silver" since that is the specific layer that gets destroyed.


Louise

[i<3ciencias]

and it's just called the silver layer?

just wondering, bc i have found like 3 articles on the parts of cds and the dyes and that stuff, and it hasn't mentioned a silver layer.

but i will check it out.

[i<3ciencias]

so my teacher told my partner and i, to create a light source acting as the sun, to use halogen lamps, but i havn't read anything that says they are damaging or anything, because if they were, they couldn't sell them to the public, right? that's wht you can't buy those UV bulbs? so just wondering, will this be a close recreation of the sun, or will this not work at all?

[Louise]

I'm going to answer both your posts with one.

From the wikipedia page I put in my first email "A thin layer of Super Purity Aluminium (or rarely gold, used for its data longevity, such as in some limited-edition audiophile CDs) is applied to the surface to make it reflective, which is protected by a film of lacquer" From the section on CD-RWs- "CD-RW disc contains a phase-change alloy recording layer composed of a phase change material, most often AgInSbTe, an alloy of silver, indium, antimony and tellurium." [Important note- CD-RW and CDs are somewhat different, so don't use don't mix them up] Other websites that I looked at say that a silver layer over nickel layer is used. You need to research what is used for your brand of CD that you are testing. You also need to read the links we provide- I should not have to provide a summary of wikipedia to you.

Question 2:
Well, halogen lamps and the sun have different amounts of different colors. This is quantified by the spectra (spectrum). So, you would want to compare the spectrum of the sun to the spectrum of the halogen lamp. You should be able to find this information on the internet. I'd start with wikipedia- there science sections are usually pretty good. The key question is "do both sunlight and my replacement light (lamp) produce light at the wavelength (color) that I propose damages CDs?"

As for if halogen lamps are damaging- lots of things are damaging that you can buy. In fact, many places do not sell halogen lamps- mostly because they get very hot and start fires. You could easily burn yourself with this type of bulb. Do they put out a lot of UV light? I have no idea. You will need to research this. However, whatever light source you use, you should NEVER look directly at the bulb. It is best if you wear plastic goggles which will help absorb UV light from whatever light source you use. You should talk to your teacher about the safety aspects.

There are more expensive bulbs that are designed to reproduce the sunlight more accurately- they are generally called full spectrum bulbs- but the precise spectrum varies from brand to brand.

Louise

[Louise]

and it's just called the silver layer?

just wondering, bc i have found like 3 articles on the parts of cds and the dyes and that stuff, and it hasn't mentioned a silver layer.

but i will check it out.

Let me just answer this post again in a different way... DKirby answered your question about how cds are destroyed by saying that the silver layer is attacked. You do need to verify this for yourself with some citation (neither "DKirby" or "Louise" is a valid citation for a science fair paper. ) I think DKirby is correct, based on my research on this topic. However, you need to be certain that this statement is correct since it is your science fair.


Louise

[i<3ciencias]

thank you for your help.

and i have read the wikipedia source you sent me,
about 3 weeks ago when i attempted my first science idea.
and scine we are not allowed to use wikipedia as a source for our papers, i did go down to the bottom and use the sources that they used to write the selection on wikipedia.

[Louise]

thank you for your help.

and i have read the wikipedia source you sent me,
about 3 weeks ago when i attempted my first science idea.
and scine we are not allowed to use wikipedia as a source for our papers, i did go down to the bottom and use the sources that they used to write the selection on wikipedia.

I think that not using wikipedia as an official source is an excellent policy. However, it did contain the answer to your question, which you needed to do your research effectively. In general, the internet is a great source for finding out simple answers ("what is the silver layer of a cd made of?" or "what is the spectrum of sunlight?") You need to know these answers before you can design a good experiment. Then you can find good (permanent) citations. Your school or local librarian would be a good person to ask if you need help finding a specific resource. I imagine a regular encyclopedia would have many of the same entries as wikipedia.

The experts on this board are here to help you with questions that are too hard for google or wikipedia. If it is on wikipedia, and an expert already pointed you to the article, then that question is too easy to ask here.

I think your project is very interesting, and I think you could do several very interesting experiments. Have you decided what question you are going to test?

Louise

[i<3ciencias]

i think i found the information i needed.

i have decided to test the preformance of recordable CDs after exposing them to extreeme conditions (light, heat, cold, etc.)

[Louise]

i think i found the information i needed.

i have decided to test the preformance of recordable CDs after exposing them to extreeme conditions (light, heat, cold, etc.)

How are you going to quantify performance? Number of skips or just by ear? You could also hold the CD up to the light and count the number of holes in the metal layer you see.

You may want get the specification sheet for whatever CD-R you are using- it seems like each brand has its own choice of metal. The website for the manufacturer should tell you what metal you testing.

Lastly, you may want to google and see what brand of CD-R people really hate... a poor quality CD-R may be more likely to degrade in your tests- it would really be unforetunate if you couldn't destroy your CDs enough to see (hear) a difference.

Have fun.
Louise

[i<3ciencias]

pur physics department has a program that you play a song on and it shows you the shape of the soundwaves through out the entire song, and gives you a picture of the whole song.

also, we were going to test different price ranges also of CD-Rs.

[Louise]

pur physics department has a program that you play a song on and it shows you the shape of the soundwaves through out the entire song, and gives you a picture of the whole song.

also, we were going to test different price ranges also of CD-Rs.

That is very cool. I think testing the different price ranges is a good idea... more expensive CDs might degrade less.

Good luck.

Louise