Nick

We bought some table lamps for the bedroom from B&Q. You turn them off & through 3 brightness levels by touching the base. How do these things work?

Wurzel

iTrader: (1)

Magic

suprabeast

probably resistance to a grounded source and a comparitor

Moonloops

Nawp - deffo Magic as Wurzel said

suprabeast

i stand corrected

OllyK

A pixie in the base actually

ALi-B

iTrader: (1)

Your body conducts electrickery, the magic fairy detects the minute current flow and flicks a few switches for you

Apparition

And here's the best bit..... it's not just the base, you can touch ANY metal bit of the lamp ! COR !
Yve

It is advisable NOT to touch the metal bulb holder however when there's no bulb in it and the lamp is plugged in. Shocking .

Nick

OK, wifey & I have a little bet on this.

I'm saying that it's detecting an earth leakage, wifey says that it detects heat. No-one wins if it's a fairy.

If I touch with my finger, the light goes on & off etc. If I touch with my fingernail - nothing happens. Touching holding something made of metal - nothing happens. Wifey claims that touching it with cold & wet hands - nothing happens. I'm not crazy enough to touch an electrical item with wet hands!

OllyK

Try
with thin latex gloves
with a cigarette lighter

Leslie

Capacitance.

Les

suprabeast

once when i turned the tv on the static caused it to turn on!

the lamp is sitting on the tv obviously

Nick

What's capacitance Les?

The light works when:
Touching with thin latex gloves

The light does not work when:
Touching holding coin
Touching holding screwdriver (the tool, not the drink)
Touching wearing marigolds

The final test which has indeed won my the "special favour" *cough*, was touching the lamp with one of wifey's face cream pots that has a metal lid. Holding the lid on the pot made the light work, holding the glass bottom did not. It looks that the lamp requires a fair contact surface.

Thanks guys

ru'

+1, although 'impedance change' may be more accurate?

Jay m A

iTrader: (2)

I'd go for capacitance too

Nezz10

The word "capacitance" has as its root the word "capacity" -- capacitance is the capacity an object has to hold electrons. The lamp, when standing by itself on a table, has a certain capacitance. This means that if a circuit tried to charge the lamp with electrons, it would take a certain number to "fill it." When you touch the lamp, your body adds to its capacity. It takes more electrons to fill you and the lamp, and the circuit detects that difference. It is even possible to buy little plug-in boxes that can turn any lamp into a touch-sensitive lamp. They work on the same principle.
Many touch-sensitive lamps have three brightness settings even though they do not use three-way bulbs. The circuit is changing the brightness of the lamp by changing the "duty cycle" of the power reaching the bulb. A bulb with a normal light switch gets "full power." Imagine, however, that you were you were to rapidly turn the power to the bulb on and off (say 100 times per second) -- then the bulb would only burn half as brightly because its duty cycle is 50 percent (half on, half off). "Rapidly switching the bulb on and off" is the basic idea used to change the brightness of the lamp -- the circuit uses zero percent (off), 33 percent, 66 percent and 100 percent duty cycles to control the lamp's brightness.

Brendan Hughes

What about touching while wearing thick rubber-soled shoes??

fast bloke

Nezz10 - does that mean that if you pulg yourself into the mains and fill up with electrons then touching the lamp wont work?

J4CKO

iTrader: (1)

Try with your *****, neat party piece !

SWRTWannabe

http://home.howstuffworks.com/question42.htm

Nick

Capacitance it is then guys, thanks!

Do I win the wifey bet?

island991

how about the fact that we have these lights but the base isnt metal??!!!! Its a china base of some sort? how the **** that work??!!

Ian_S

We had them and once the bulb blew they stopped working, and yes, the bulb was replaced with working new ones.

Nick

I thought about it, but couldn't do it!

dsmith

not long enough ?

Brendan Hughes

Remarkable! Did Nezz10 write that article for them? It seems to be very similar to his explanation above.

Nick

That wasn't the reason, would you use your plonker for testing electricty?