Why do touch lamps need skin contact to work? Why won’t my book work?

Touch lamps have been around since the mid-1980s and they are still über cool. There’s something very Jetsons about tapping a lamp to turn it on and off.

A touch sensitive lampThe technology that makes them work is the same technology that makes touch screen mobile devices work – albeit in a much more basic form. It is called capacitive sensing and relies on the electrical properties of the human body.

Within the metal housing of the lamp, there is a very small electrical charge. The electronics inside the lamp control this charge – ‘flipping’ it very quickly between a positive and a negative charge (in the same way that AC, or alternating current, in the mains power is constantly changing). Silicon chips inside the lamp detect the small amount of charge that is moving through the metal.

Like metal, your body also conducts electricity. When you touch the metal base of the lamp, the moving electrical charge is no longer just passing into the metal but also into you – it is ‘electrifying’ you. (Not ‘electrocuting’ you – that would be very bad.) The microchips inside the lamp detect that there is now more charge flowing, triggering the on/off switch.

Your book doesn’t work because paper doesn’t conduct electricity. Similarly, a gloved finger won’t work (you will probably know this from trying to work your touchscreen phone with gloves on).

You could buy conductive gloves but I’m going to hold out for a lamp that ‘knows’ when you’ve stopped reading and want to go to sleep. Not that would be the ultimate in laziness.

Answer by Dr Stu

Question from Nicky via Facebook

Image source: i.m.indraneel on Flickr

Article by Stuart Farrimond

February 17, 2014

Doctor Stu is editor of Guru Magazine. He originally trained as a medical doctor before deciding to branch out into lecturing, writing, editing and science communication. He drinks far too much coffee, eats lots of ice cream and has a bizarre love of keeping fit.
You can check out Doctor Stu’s blog at realdoctorstu.com or his poncy personal website stuartfarrimond.com. Here's his .

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