Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why do lamps need two twists?

  1. Jan 29, 2006 #1
    On most lamps that I've come seen, they have a round knob that you rotate to turn the lamp on and off, and it clicks when you do that. Every one of those lamps requires TWO twists of the knob to do anything (two to turn it on, another two to turn it off). Why do they make them that way? Wouldn't it be easier to just turn it once?
     
  2. jcsd
  3. Jan 29, 2006 #2
    I only have one of these lamps in the house. It only takes one click. Two-click knobs are obviously a conspiracy.
     
  4. Jan 29, 2006 #3
    The reason for this is that some lamp fixtures are pre-designed to house 2-way and 3-way bulbs. What this means is that those types of light bulbs have either 2 or 3 illumination settings. This is common in house lamps.
    Now, if you place a standard bulb into one of those fixtures, often only the last "click" will turn on the bulb if the bulb watt ratting is high(say, 68-watts)
    If you placed, say, a 40-watt standard bulb into one of those fixtures, the first "click" might light the bulb.
     
    Last edited: Jan 29, 2006
  5. Jan 29, 2006 #4
    I have only noticed 2 clicks to do anything. Every other click actually does something. The way it works is there are 2 filaments. One 40 and one 60 watt filament. The first position on the switch neither filament is energized. The second position only the 40 is energized. The third position only the 60 is energized. The last position both are energized for 100 watts.
     
  6. Jan 29, 2006 #5
    Thanks guys. It makes sense to me now.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?