MadSci Network: Computer Science

Re: Flourescent light and modem

Date: Thu Feb 11 01:17:11 1999
Posted By: Abtin Spantman, , Electrical Engineering, L. S. Research, Inc.
Area of science: Computer Science
ID: 915882917.Cs

Your question has two parts:
1) Can Fluorescent lights interfere with modem operation?
2) How can light interfere with the flow of electricity?

The answers are:
1) Yes.
2) It is not the light that is causing the problem.

A modem transfers information by transferring energy in the form of electrical signals through a wire. Electrical signals are actually made up of electrical and magnetic components. These electrical and magnetic (EM) components of the energy are radiated in all directions, and the wire only facilitates the flow of this energy through it. Imagine a balloon filled with air with a straw stuck in it. The air puts pressure in all directions, but can't go anywhere except through the straw. Now imagine the sound (of someone talking) being in the balloon along with the air, and flowing through the straw- that would be your data. A wire does the same thing for electric signals (EM energy), it allows the signal to flow through the wire more freely than in the air. An antenna is a perfect example. It picks up EM energy that is in the air and all around us, and that energy is what appears as an electrical signal through the antenna. The phone wire that is attached to the modem is like a big antenna, picking up energy from the outside, and adding to the energy from the modem. This outside energy is called "noise" on the system.

Some of the newer "energy efficient" fluorescent light fixtures have switching supplies that operate at higher voltages (around 240 volts) and frequencies (around 300kHz). At those voltages and frequencies, these switching supplies radiate EM energy, which is similar to that of the modems. This energy from the fluorescent power supply is picked up by the modem's phone wire (antenna), and is seen by the modem system as noise. Lastly, lets see why modem seems to slow down. The modem can not distinguish between the EM energy of the data signal and the EM energy from the fluorescent power supply. That would be like two people trying to talk at you at the same time. In order to understand them, you have to make both stop talking, and only one person to talk and repeat themselves. The modems have to do the same thing in the presence of outside noise. This necessity to repeat a communication many times is what slows down modems. Some of the newer modems have automatic detection features that try to communicate as fast as possible, with no errors. If any errors are detected, then the modem tries to re-send the data. If there are still, a lot of errors, then the modems automatically switch to a slower speed and try everything over again until they send all the information over without any errors.

And that is why modems slow down in the presence of some fluorescent light fixtures.

What I didn't tell you is that light is also EM energy. Can you tell me why I said the problem is the switching supply and not the light?

Abtin Spantman

Current Queue | Current Queue for Computer Science | Computer Science archives

Try the links in the MadSci Library for more information on Computer Science.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1999. All rights reserved.