View source for Balanced-arm lamp

{{short description|Lamp with an adjustable balanced folding arm}}
[[File:Anglepoise 1227.jpg|thumb|Anglepoise model 1227 from 1935]]
A '''balanced-arm lamp''', sometimes called a '''floating arm lamp''', is a lamp with an adjustable folding arm which is constructed such that the force due to gravity is always counteracted by springs, regardless of the position of the arms of the lamp. Many lamp brands (such as the [[Anglepoise lamp|Anglepoise]], originator of the concept, and [[Luxo]] L-1), as well as other devices, use this principle.

==Configuration==
=== The five terms ===

This article uses the terminology:
[[Image:Compare human arm.PNG|right|200px]]
* ''lamp cap'',
* ''forearm'', 
* ''upper arm'',
* ''stand'' or ''body'' and
* ''base''
for the five basic parts of these lamps.

=== The general design ===
A balanced-arm lamp has a ''base'', a ''stand'' or ''body'', (in most cases) ''two'' connected ''arms'' (in many cases fitted with springs), and a ''lamp-head''.

The lamp can be moved into almost any position, and the balancing device will maintain the position until moved again.

The same overall mechanism can be employed in ''other'' devices with similar requirements, such as:
* copy holders for typists,
* microphone holders in studios or
* computer display holders.

For the [[physics]] and theory behind balanced-arm lamps, see [[Classical mechanics]], [[Linkage (mechanical)|linkage]] and [[torque]].

There are different methods to balance the arms and the lamp-cap:
* [[coil spring]]s<br>In some cases a set of ''two'' coil springs working in parallel on both sides of the pivoting arm is used.<br>(They function in the same way as a ''single'' spring.)
* [[counterweight]](s)<br>(a method frequently used in [[Sash window]]s and [[drawing board]]s).
* [[Friction]] between parts of the lamp arm,
* Coupling or
* hydraulics or pneumatic arms.

==Lamps balanced with springs==
[[Image:Pressure and expansion springs.PNG|thumb|right|100px|Compression and tension springs at rest and under load]]
There are many variations of construction with [[Spring (device)|springs]]. Springs can be located on the mechanical equivalent of the forearm or the upper arm, or both, as well as nearer to the base. Some lamps use tension springs, and others use compression springs. The adjacent image shows (left to right) a compression spring at rest, then under load, followed by a tension spring at rest, and then under load. 
Springs have a limited lifting capacity and extension length.
Some springs can resonate, producing low-level unwanted noise.
{{clear}}

===One tension spring===
==== Spring-balanced upper arm, flexible forearm ====
[[File:extension spring balanced arm support a flexible arm.PNG|border|right|300px|alt=A flexible forearm|A flexible forearm]]
This lamp has a stiff flexible tube as its forearm, and a spring-balanced arm to support it near the middle. That way there is a flexible lamp with a long reach.
{{clear}}

==== Tension spring over wheels ====
[[File:Extension spring rolls over 2 wheels.PNG|border|right|300px|alt=A spring over two wheels|A spring over two wheels]]
The wheel to control the forearm is smaller than the wheel that controls the upper arm.
The lamp cap rotates the same direction as the upper arm and forearm.
{{clear}}

==== Two arms, one spring, one toothed wheel ====
[[File:2 arm 1 spring 1 Tooth wheel.PNG|border|right|500px|alt=A single spring controlling upper arm and forearm|A single spring controlling upper arm and forearm]]
With this technique the tension spring has a double function: it controls both the forearm and the upper arm. This is not a common arm lamp system.
The lamp cap rotates the same direction as the upper arm and forearm.
{{clear}}

===Two tension springs===
==== Two parallelograms and two tension [[Spring (device)|spring]] sets ====
[[File:upper-arm 3 bars parallel.jpg|border|right|75px|alt=An upper arm showing three parallel bars|An upper arm showing three parallel bars]]
One tension spring set controls the forearm, which is a [[parallelogram]] having two bars. A stronger spring set controls the upper arm, which has three parallel bars (see photo, left). (There is a less stable construction with two parallel bars in the upper arm which is less expensive to manufacture.) Due to the parallel [[Linkage (mechanical)|linkage]] of the lamp, the lamp cap keeps pointing in the same vertical direction when adjusting the height of the lamp. As with most balanced-arm lamps, the whole assembly can rotate in the horizontal plane, and is mounted on a stable foot.
{{clear}}

==== One parallelogram and two extension spring sets ====
[[File:Angle Poise Lamp Diagram 2.png|border|right|300px|Anglepoise-style lamp]]
A lamp like the [[Anglepoise lamp]] has one [[parallelogram]] and two extension springs. One spring controls the shortest arm of a parallelogram. Parallel to this shortest arm there is the forearm. To keep these arms parallel there are two other parallel arms (upper arm) that are controlled by a second extension spring.
The lamp cap rotates the same direction as the upper arm and forearm.
{{clear}}

==== Single forearm bar, one parallelogram, two tension spring sets ====
[[File:single Lamp arm, parralellogram ,2extension springs.PNG|border|right|300px|alt=Diagram of a single-forearm lamp|Diagram of a single-forearm lamp]]
The forearm of this lamp consist of a single bar. When it is adjusted, the angle of the lamp cap changes along with the arm.
{{clear}}

==== Tension springs within the arms ====
[[File:lamp 2x arm, cable, extension springs.PNG|border|right|300px|alt=Tension springs within the arms|Tension springs within the arms]]
A lamp like the [[Tolomeo desk lamp]] has no [[parallelogram]]s in either arm. In this modern lamp the tension springs are hidden in the arms. The lamp cap rotates the same direction as the upper arm and forearm.
{{clear}}

===Compression springs===

==== Compression springs in the arms ====
[[File:2 compression springs 1 parallelogram lamp.PNG|border|right|400px|alt=Compression springs in the arms|Compression springs in the arms]]
The short arms (green) stay parallel. One spring puts pull [[force]] on the blue arm. (If the blue arm is tilted back the second spring on this arm gets push force.) The blue arm controls the two parallel arms (red) that make up the upper arm. The other spring puts pull force on the other blue arm. This arm controls the forearm (magenta). The two springs can be the same size; one spring has to lift more [[weight]] but is more vertical. The other spring lifts less weight but is more horizontal.
{{clear}}

==== Compression springs near the foot ====
[[File:spring balanced bending arm lamp.JPG|border|right|300px|alt=Spring-balanced bending arm lamp|Spring-balanced bending arm lamp]]
One compression spring controls a very short arm (grey). The [[Roller chain]] [[Wire rope|cable]] connects this arm parallel to the forearm (yellow). The longer spring controls the (blue) arm. The body (red) can turn in the horizontal plane. The body is connected to a stable foot. The body can be smaller because the pressure springs can protrude below the body.
{{clear}}

==== A compression spring with one parallelogram ====
[[File:One Pressure spring one parallelogram.PNG|border|right|250px|alt=A compression spring with one parallelogram|A compression spring with one parallelogram]]
In this method, just one compression spring controls a [[pantographic arm]].
{{clear}}

<!-- Removing this section because these lamps have never existed beyond patent concepts

===Other types of spring===

{| style="width: 100%; background-color: inherit;"
!colspan="1"| Spiral spring controls a pantograph arm
|-
| [[Image:Spiral spring controls a pantograph arm lamp.PNG|400px|right|Spiral spring]] Patent: GB1290891A from 1970
|-
|}

{| style="width: 100%; background-color: inherit;"
!colspan="1"| Torsion springs control the pivoting arm
|-
| [[Image:2 torsion springs balanced arm lamp.PNG|400px|right|Torsion springs]]
|-
|}

-->

==Lamps balanced by pressure and friction==

=== Rubber between two "parallel" arms ===
In this construction (commonly found in Italian lamps) gravity causes the parallelogram to deform such that the gap between the long arms becomes smaller. This in turn increases pressure on the [[rubber]] in the gap, and the resulting [[friction]] holds the arm in place.

{{multiple image
   | width     = 300
   | footer    = The arms are balanced by pressure and friction
   | image1    = friction rubber arm lamp.PNG
   | alt1      = Friction rubber arm
   | caption1  = Friction rubber arm
   | image2    = squeezing rubber arm lamp outer position.PNG
   | alt2      = Squeezing rubber arm
   | caption2  = Squeezing rubber arm}}

{{clear}}

=== Friction from twisting ===
[[File:flexeble bars lamp.PNG|border|right|500px|alt=Lamp with flexible bars|Lamp with flexible bars]]
The [[friction]] between the twisted arm controls the movement between the arms.
{{clear}}

=== Friction between the ''upper'' arm and the ''fore''arm ===
[[File:Tighten bold friction arm system.PNG|border|right|200px|alt=Another lamp with flexible bars|Another lamp with flexible bars]]
This arm system also works with friction.
{{clear}}

== Lamps balanced with counterweight ==
=== Lamps balanced with ''one'' counterweight ===
Advantages of one swinging counterbalance is that the lamp can have a longer arm length.

Disadvantages are that the lamp is inherently less balanced, thus it needs a heavy stand to remain stable.
    
==== A single counterweight ====
[[File:1 weight chain lamp.PNG|border|right|300px|alt=Single weight chain lamp|Single weight chain lamp]]
This construction uses a chain to keep the arm with the [[counterweight]] and the forearm parallel. The lamp-cap and counterweight move in opposite directions (both away from the base or both towards it). The balance that is required is shown by the following formula:

:d<sub>1</sub> = Lamp-cap to base; m<sub>1</sub> = weight of lamp-cap

:d<sub>2</sub> = counterweight to base; m<sub>2</sub> = weight of counterweight

:m<sub>1</sub> × d<sub>1</sub> = m<sub>2</sub> × d<sub>2</sub>
{{clear}}

==== One parallelogram with one counterweight ====
[[File:1 Parallelogram + 1 Counterweight.PNG|border|right|300px|alt=One parallelogram and one counterweight|One parallelogram and one counterweight]]
This lamp  has a heavy base, with a parallelogram [[pantograph]] construction formed by bars which are all hinged on each other. One long bar extends past the parallelogram construction and has a [[counterweight]]. One short bar also extends past the parallelogram construction and holds the lamp cap.
The base has an arc formed stand so the counterweight does not hit the stand in vertical position. 
{{clear}}

==== One parallelogram with an extended counterweight ====
[[File:Pantographic parallel arms balance a light-weight-lamp and counter-weight.gif|border|right|200px]]
This lamp is similar to the one above, but as the counterweight has a low position the lamp needs no heavy foot for [[mechanical equilibrium|stability]] as the center of gravity is low.
The counterbalance does not swing, but slides and rotates safely around the center of the stand.
{{clear}}

==== Three parallelograms with one counterweight ====
[[File:Complex counter weight arm lamp.PNG|border|right|500px]]
This lamp stand has a complex construction with matching narrow openings.
This lamp is out of production.
{{clear}}

=== Lamps balanced with ''two'' counterweights ===

==== A single arm with two counterweights ====
[[File:Counter balanced straight arm lamp.PNG|border|right|300px]]
With this lamp the movement is very limited (the arm moves up and down only) but the technique is nice to look at. As the forearm becomes more horizontal the [[weight]] ceases to be balanced on both side of the base. The weight of the base is needed to avoid over-balancing.
<!--Lamp-cap x fore-Arm = (Arm 1 x weight 1) + (Arm 2 x weight 2)-->
{{clear}}

==== Two arms with two counterweights ====
{{multiple image
| align             = left
| width             = 200
| image1            = Lamp 2 counter weight.PNG
| alt1              = Dimension diagram
| caption1          = Dimension diagram
| image2            = Lamp 2 arms 2 counter weights outer position.PNG
| alt2              = Outer position
| caption2          = Outer position
| footer            = Lamp with two arms and two counterweights
| image3            = New_Lamp_2_arms_2_counter_weights_outer_position.png
| alt3              = New Correct Diagram
| caption3          = New Correct Diagram
}}

A lamp type like the [[Tizio]] works like this. A balancing arm (the forearm) has on one side of an axis a small [[counterweight]] and on the other side a lamp cap. These parts are lifted by a second bigger balancing arm (the upper arm) that has on the other side of a second axis a heavier counterweight. The lamp designed by Edouard-Wilfrid Buquet in 1927 works in this way. The lamp is in the collection of the [[Museum of Modern Art]]. The two axes have a different angle, and this has some advantages.

Lamp-cap x fore-Arm = Arm x Small weight (Lamp-cap + Small weight) x upper-arm = Arm x Big weight.
[[File:Big and small counterweight arm-lamp.gif||right|300px]]
{{clear}}

== Lamps using other systems ==

Here are some less common ways of balancing arms.

=== Lamps having a vertical axis ===
[[File:arm-lamps having a vertical axis.PNG|border|right|325px|alt=Lamps having a vertical axis|Lamps having a vertical axis]]
This kind of lamp has a forearm balanced by weight or springs. Its disadvantage is that the upper arm cannot point up or forwards.
{{clear}}

=== Mechanical coupling devices ===
[[File:Mechanical locking joint.PNG|border|right|200px|alt=Mechanical locking jointlamp|Mechanical locking jointlamp]]
This lamp works by [[Couple (mechanics)|coupling]] together the upper arm and the forearm. It is called a gravity-locked or cam-locked elbow.<ref>[http://www.tribtech.com/app.20.htm See here]</ref>
{{clear}}

=== Hydraulic arm ===
[[File:GraphyArchy - Wikipedia 00323.jpg|thumb|upright|Moving streetlamps in [[Rotterdam]]]]
The pivoting arm [[streetlamp]]s in the [[Schouwburgplein (Rotterdam)|Schouwburgplein, Rotterdam]] use a pair of [[hydraulic cylinder]]s to control the forearm and upper arm.

{{clear}}

=== Pneumatic arm ===
[[File:pneumatic arm lamp.PNG|border|right|300px]]
Arm lamp with a [[pneumatic cylinder]]. The gravity compress the air in the pneumatic cylinder.
{{clear}}

==In popular culture==

* Two spring-balanced desk lamps of this type feature as the main characters in the 1986 [[Pixar]] short film ''[[Luxo Jr.]]''. It also serves as the letter I in the Pixar logo presented before and at the end of each of their films.
* [[Myster Shadow-Sky]] is the only composer who from 1980 to 2007 performed the balanced-arm lamp as a musical instrument: the archisonic lamp. In 1980 he wrote the score "Ludus Musicae Temporarium" for a balanced arm lamp orchestra. The world premiere was performed by [[Les Percussions de Strasbourg]] at the Manca contemporary music festival in Nice in 1988. He released five albums with a four spring balanced arm lamp musical instrument (and more with other musical instruments). They are available for free download.<ref>{{Cite web|url=http://centrebombe.org/myster_shadow-sky_discography.html|title=Rebel'n adventurous myster shadow-sky's free discography}}</ref> Referenced in the book "Les chercheurs de sons" (2004), as the unique creator of a balanced arm lamp as a musical instrument.

==See also==
{{Commons category|Balanced-arm lamps}}
{{div col}}
* [[Engineering science and mechanics]] 
* [[Gooseneck lamp]]
* [[Industrial design]]
* [[Light fixture]]
* [[Mechanical advantage]]
* [[Mechanical engineering technology]]
* [[Moment (physics)]]
* [[Torsion spring]]
{{div col end}}

==Patents history==

Classifications IPC: F21V21/26

International patent category: B23B31/171
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB191104491 GB191104491] An Improved Device for Supporting or Suspending Electric Lamps and the like (1911)
* {{US patent|1370231}} - 1921 harmonica arm
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB206435 GB206435] 1923 parallelogram & counter weight
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB254972 GB254972] 1926 friction
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB285045 GB285045] 1929 2 counter weight
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB481198 GB481198] 1934 spring and counter weight
* FR757890 1934 CARWARDINE GEORGE
* FR784932 1935 CARWARDINE GEORGE
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB470502 GB470502] 1937 friction
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB489547 GB489547] 1938 2 parallelogram 2 springs 
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB504791 GB504791] 1939 2 pressure springs
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB536342 GB536342] 19..  a-symmetric arm-lamp
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB589994 GB589994] 1947 friction and a spring
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB618344 GB618344] 1949 
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB629364 GB629364] 1949 spring in the arm
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB713378 GB713378] 1954 friction arm

* {{US patent|3003737A11961}}  1961
* [http://www.delphion.com/cgi-bin/viewpat.cmd/GB1249774A GB1249774A] 1971
* {{US patent|5333103A1}} 1991 
* EP0518569 1992
* EP1274545  2003  mechanical coupling devices

<!-- UNUSED TABLE: I don't understand it, so it probably needs an accompanying explanation at least. I feel it probably duplicates info on other pages. 
{| border=1 cellspacing=0 cellpadding=5

! 
! Force
! ×
! Distance
! +
! Force
! ×
! Distance
! =
! Moment
! =
! Force
| ×
! Distance

|-

|| ||Newtons(N)|| ×|| Metres (m)|| +|| Newtons (N)|| ×|| Metres (m)|| =|| Newton-metre (Nm)|| =|| Newtons (N)|| ×|| Metres (m)
|-
|| || Weight 
Lamp-cap|| || Distance
Lamp-cap|| || Weight 
arm|| || Distance
middle-
arm|| || On the pivot|| || Distance
counter balance|| || weight
counter balance

|-

|| high reach|| 4 N|| ×|| 1 m|| +|| 2 N|| ×|| 0.5 m|| =|| 5  (Nm)|| =|| 0.125 m|| ×|| 40 N

|-
||Long reach|| 4 N|| ×|| 1.5 m|| +|| 2 N|| ×|| 0.75 m|| =|| 7.5 (Nm)|| =|| 0.187 m|| ×|| 40 N

|-
||reach|| 4 N|| ×|| 1.4 m|| +|| 2 N|| ×|| 0.70 m|| =|| 7  (Nm)|| =|| 0.175 m|| ×|| 40 N

|-
||Low reach|| 4 N|| ×|| 900 m|| +|| 2 N|| ×|| 0.45 m|| =|| 4.5 (Nm)|| =|| 0.112 m
 ×|| 40 N

|}554555445
-->

<!--UNUSED IMAGES
[[Image:Stretch Pantographic parallel balance arm a light-weight-lamp and counter-weight.PNG|300px]]
[[Image:Bending Pantographic parallel balance arm a light-weight-lamp and counter-weight.PNG|300px]]
[[Image:pressure spring controls a  photographic arm.PNG|300px|left|One compression spring controls a pantographic arm]]
[[Image:Popular American lamp.PNG|thumb|left|Popular American lamp]]
-->

==References==
<references/>

{{Artificial light sources}}

[[Category:Light fixtures]]