Science Buddies: "Ask an Expert"

1.) Is it important to know how to measure light intensity?
2.) Who invented the LUX Meter?
3.) Where is the most intense measure of light from a lamp?
4.) Why does light intensity change with distance?
5.) How does a LUX Meter work?
6.) How do you measure light intensity?
7.) How does a LUX Meter detect light intensity?
8.) When was light intensity difference discovered?
9.) What is needed to build a LUX Meter?
10.) When was the first LUX Meter invented?

Hello and my son, Patrick Gallagher, is a 7th grader. He is doing his science project on the LUX Meter and light intensity. He has prepared the above 10 questions and his next step is to ask a specialist in this field and record the responses.

When you have an opportunity, he would greatly appreciate your assistance. His due date for submitting his questions with the answers is DECEMBER 13TH.

Thank you so very much for your time and assistance regarding my son's science fair project.

Pam Gallagher

Hi,

Here is a Science Buddies Project that explains light intensity versus distance from the light source:

https://www.sciencebuddies.org/science- ... p034.shtml

Here is a Wikipedia article on light meters that describes how several types of meters work and cites Don Norwood as the inventor of one type:

http://en.wikipedia.org/wiki/Light_meter

I think if you look into it the LUX meter has been improved by several inventors over time. Here is a recent patent:

http://www.freepatentsonline.com/3972626.pdf

If you are interested you can use the patent numbers cited in ”References Cited” section at the beginning of the patent to find and view ealier inventors of related items using the US Patent Office search engine at:

http://patft.uspto.gov/netahtml/PTO/search-bool.html

How do you design/build a LUX meter? Here is a student report of such a project ( the English is poor):

http://fetweb.ju.edu.jo/staff/Mechatron ... xmeter.pdf

Here is another project idea:
http://elm-chan.org/works/lux/report.html

I think if you look at these resources carefully most of your questions will be answered. If not, post back with the ones I missed.

Good luck and have fun!

Best regards,

Barrett L Tomlinson

Add to the prior response two more Wikipedia articles:
http://en.wikipedia.org/wiki/Lux
http://en.wikipedia.org/wiki/Lumen_(unit)

As to how llight intensity is measured, a photocell converts light signals into electrical signals. Some do it by producing actual electrical current (photovoltiac, silicon photo cell) and others do it by changing a resistance (photoresistive, cadmium sulfide). The actual mechanism requires an understanding of quantum physics, don't worry about that part yet. Once that transformation has been done, everything else is just processing and indicating the electrical values.

#1, Why
If you want to build something yourself, probably no big deal, but if you want someone else to build it you need to be able to tell them how. How sensitive are your eyes? Can you see in the dark, dim, bright, very bright? How bright is bright enough?

#3, Just like a fire, closer is hotter, closer is brighter. Same amount of fire and the same amout of light, but when you are closer you get more energy per unit of area. Look at the inverse square law.

#8, About the same evening that some cave man looked up and noticed that some stars are bright and some are dim, thus differences in light intensity or brightness was discovered.

#10, Not sure but probably at least 1000 years ago. Compare a candle to the light source in question and decide if the unknown light is more or less bright, that is a meter. Crude, but everything starts out that way and gets refined as the technology improves.