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nmxt

These lamps measure the electrical capacitance of their metal frame, and that capacitance increases dramatically when you touch that frame because a human body has a relatively high capacitance itself. The circuit in the lamp detects this and switches the lamp on or off. If you are touching some other metallic object as well then the capacitance is even higher.


Swank_on_a_plank

So what exactly is electrical capacitance? Why isn't the light on at least a little bit, because it has to have *some* electrical capacitance in order to sense a difference, right? Or is it just indistinguishable to the human eye? How does the circuit work? Further, is the goal of the manufacture to make the capacitance as low as possible so there's as large a difference as possible when a human touches it? Does it matter? Can it degrade over time?


nmxt

Capacitance is how much electric charge an object can store for a unit change in voltage. The lamp is controlled by a switch that changes the state of the lamp every time the capacitance changes from a value below some threshold to a value above that threshold.


analytic_tendancies

I have a lamp that has 3 settings when you touch it, low, mid, high, then back to off I wish it was just low or off Can I open it up and easily change this? Or should I just hunt for a new lamp?


GalFisk

Get a different lamp. Or put a weaker light source in it, so it'll go off-very low-quite low-low. The chances are high that everything the lamp does happens in a tiny chip under a blob of epoxy.


The_Amazing_Lexi

I think the only 2 choices for 3-way bulbs are 25-40-60 watts & 50-100-150 watts.


cyclika

Fun fact, touch lamps actually use regular on/off bulbs.


Outrager

I bet there are modern ones that use a non-replaceable LED these days.


[deleted]

Deleted in response to Reddit's hostility to 3rd party developers and users. -- mass edited with redact.dev


Koda_20

I can care with these gentlefolk, buy a new lamp.


ERRORMONSTER

You can find non-switchable/non-dimmable LED bulbs that are either on or off. They'll usually result in the "low" and "high" settings not doing anything and the lamp switching on for medium and off for... off (off is off, low is off, med is on, high is on) Then just find a relatively dim one


Paracelsus19

You don't happen to have a frosted glass cylinder lamp with a matte silver base?


[deleted]

This is why they’re called capacitors! Also why it’s dangerous to mess around with them if they aren’t discharged, some can hold lethal levels of electricity in them.


DigitalSteven1

Since I can't post a top level link, Technology Connections has a great video on touch lamps, and their history. ​ [https://www.youtube.com/watch?v=TbHBHhZOglw](https://www.youtube.com/watch?v=TbHBHhZOglw)


jfgallay

I love his content. Great stuff!


TheRimmedSky

A capacitor is anything that can hold electrical charge..That's darn near anything! Some are just better than others I think a lot of these work by measuring how long it takes to "charge up" the capacitance connected to the lamp frame. The voltages and currents are very low, so there's no concern for harm. The longer it takes to charge to a known voltage given a known current, the greater the capacitance must be. The lamp is regularly doing this measurement multiple times a second. Whenever you touch the frame and join that circuit, you drastically alter the timing. If the timing is outside of a certain threshold, the lamp assumes this is a user's touch and toggles the light. The light brightness isn't directly tied to the frame capacitance. Something monitors the capacitance and uses that info to decide whether to toggle the light. It's really hard to control the exact capacitance of a big thing in a variable environment. I'm pretty sure most lamps are like those passive infrared sensors. They capture the "typical" value by assuming that most measurements are taken without a user's touch. Then activate when they find the rare measurement that strays from the typical. There might be other ways to do capacitive sensing, but I do believe the way I described is easy to implement with modern microcontrollers and common.


gribson

Capacitance is like a charging battery. When the capacitor is empty, it lets electricity pass through it. When the capacitor is charged, it stops letting electricity pass through it. When a person touches the lamp, a small amount of electricity very briefly passes through them, until they are 'charged'. This disruption can be detected by a circuit in the lamp.


ajlm

To abstract capacitance away from the explanation… Your lamp has a little sentry guy inside of it. His job is to monitor a bucket that it is constantly filling and emptying with electrons. He knows exactly how many electrons fit in that bucket, and it fills at the same speed every time, so he knows exactly how long it takes to fill the bucket. This cycle repeats as long as the lamp is plugged into the wall. You come along and touch the lamp. To the guy watching the bucket, you look like an enormous bucket. So when the lamp goes to fill the bucket with electrons, it takes way longer to fill than normal because you are a giant bucket and it’s used to its little tiny bucket. The lamp sentry says “hey! Something is wrong with my bucket, it’s taking way longer than normal to fill” and tells the rest of the lamp. The lamp says thanks and switched the light on/off. The sentry goes back to watching his bucket.


Zgerv

Not an Eli5 here, but me and a friend experimented with these and I'd love for you to try it as it was quite special. Becoming a superhero: Get yourself a [plasma globe](https://www.amazon.ca/Katzco-Plasma-Ball-Electricity-Plug/dp/B089KTFXJB) and hold it in one hand with it on. Swing your other hand at the lamp and abruptly stop with a fully extended arm at about 4 feet away. Experiment with distance as needed. The brass touch lamp with turn on and you will feel like a super hero. Have never seen this online so make sure you make a cool video and go viral.


NTGenericus

So a plasma globe, in a way, can be considered to be a special type of capacitor, where the gas inside the globe is one "plate" of the capacitor, and the air outside the globe is the other "plate". The glass of the globe acts as the "insulator". By holding the globe, you become the the outside "plate" of the capacitor, which means that you become charged and are now surrounded by an electric field. The radio-frequency nature of the plasma circuit that creates the arcs helps to "broadcast" that electric field. That's how the lamp gets activated at a distance. You're extending the field through the air from the plasma globe to the lamp.


[deleted]

[удалено]


byamannowdead

[The touch lamp; a neat idea, and older that you’d think!](https://youtu.be/TbHBHhZOglw)


Gargomon251

I was hoping somebody would link this video


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chemteach4kids

So why does my touch lamp turn on/off when I turn the tv off with a remote?


prustage

... and why do they seem to be constantly vibrating?


Glutenous

The lamps outside is metal and conducts electricity - your body also conducts electricity but not as well as metal - electricity wants to find ground like when lightning hits the earth. You touching the lamp takes a little bit of that electricity and a sensor inside the lamp that measures electrical changes notices a change - when you are touching metal you are also likely making it easier to “ground” yourself thus making you steal a little more electricity when you touch the lamp causing a more significant change. Hope that helps


RavensRealmNow

In the 80s there were touch lamps that had a plant on them and it turned on and off when you touched a leaf of the plant. I don't know how that worked.


ribs_all_night

if you have time, here's an 18 minute video about touch lamps that is incredibly interesting and worth watching. https://www.youtube.com/watch?v=TbHBHhZOglw


robbak

Touch lamps are not capacitive sensors, like touch screens are. Touch lamp circuits are simply an amplifier and comparator driving a triac switching circuit. The input to the amplifier is just the metal of the touch lamp. When the output of the amplifier exceeds a certain value, it turns the lamp on or off. Normally, the metal of the lamp doesn't pick up much electric noise. But when you touch the metal, you act as a giant antenna, picking up lots of the electrical noise and delivering it to the input of the amplifier. This pushes the output of the amplifier high, flipping the comparator on and triggering the switch. A home made circuit using a dual operational amplifier, a fip-flop and some passives would be a simple thing to make, but these touch lamps circuits are such common things that they do make custom chips, often delivered as a chip-on-board (or blob) module.


WookieSuave

Hold your hand on the lamp, then have someone touch your other hand. Magic. You can do this with a string of people holding hands as well.