WiFi, Light Bulbs, And The FCC

JFMulder writes "According to Cringely, 802.11 WiFi wireless networking is going to get in lot of troubles when Fushion Lightning starts marketting low-power light blubs which causes interferences with Wifi signals. Read about it at I, Cringely. Supposedly the new kind of light bulb is a real electricity saver and can wreck havoc to wireless networks in a half a mile radius. So what would you prefer? Wireless networks or low cost light bulbs all around the country to save more and more on electricity?" Update: 06/13 03:52 GMT by M : Cringely confused the FHSS-or-DSSS 802.11 standard with the DSSS-only 802.11b standard, but the general warning about the potential for interference is certainly troubling.

Comments

For crying out loud...

[The_Deacon]

This was posted -- what, two or three weeks ago? Come on guys!

The old story even had a poster who mentioned that he'd used the lighting technology Cringley mentioned, and it's nowhere NEAR primetime, so it won't be causing probs for several years, if ever.

Re:Too much power?

[wowbagger]

It takes very little signal power to disrupt radio communications.

In radio, you measure signal power in dBm (decibels referenced to 1 mW). A typical narrowband FM receiver, like a cell phone, has a sensitivity of about -120 dBm - in other words, if the phone is getting -120 dBm at the antenna port it will just barely work. -120 dBm is one 10E-12 of 1 milliwatt - or one thousandth of a picowatt.

For a wireless LAN card, I think they usually want to see about -76 dBm for a good link - that's 10E-7.6 of a milliwatt being received, or about a twentieth of a nanowatt.

Let's say the lamp is a 5 watt lamp (and from what I understand most of these lights are more like 100 watts excitation energy - these aren't your floor lamp!) Let's say the lamp leaks .01% of its power - that would be half a milliwatt. Assume the leak is an isotropic radiator (radiates equally in all directions). So you have .5 mW (= -6 dBm) into a 0 dBi radiating antenna. Your wireless card is about +30 dBm into a +3dBi antenna - so you would have -6 dBm interference vs. +33 dBm ERP for the wireless transmitter, assuming they were both at the same place. That wouldn't be a problem.

Now, if the lamp is anything like the microwave pumped lamps I used to work with, you are talking about 500 watts or more of excitation energy - that's +20 dB. If the lamp leaks 1% of its signal (still small enough to have no real effect on the light output) that would be another +20 dB of leakage. You now have taken the lamp from -6 dBm ERP to +34 dBm - and you are now just as "loud" as the network card.

Also, these lamps are pumped by magnetron tubes, same as your microwave oven. These aren't nice, single-frequency sources - they spatter over a fair chunk of the band. So you cannot modulate them and use them as network nodes, and you cannot easily skip over the frequencies they use - they don't just impair one channel of a frequency hopping system, the impair many channels.

However, I have to wonder how the efficency of these lamps compares to the new LEDs on the market - it may be a moot point.