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Spacing and Centers

Discussion in 'Lighting and Electrics' started by TupeloTechie, Jun 9, 2008.

  1. TupeloTechie

    TupeloTechie Active Member

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    I'm a little confused about a couple of things, both spacing and the term "centers". When these books that I read talk about spacing, such as on "1'6" on center" what exactly are they talking about? And how does this refer to creation of light plots?

    Somebody help me, I am so confused!

    Thanks ~Paul
     
  2. SteveB

    SteveB Well-Known Member

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    Lighting units hung on a lighting position, need to be mounted in such a way so the instrument can focus to the desired location. This means the unit must have a certain amount of space around it to focus.

    Typically, and on a horizontal lighting position, such as a truss or electric pipe, an ellipsoidal might need about 1'-6" of space between it and any adjacent ellipsoidals, as measured from c-clamp to c-clamp, or center of unit to center of unit (in the case of moving lights).

    Different units need more or less space, depending on the intended focus and or unit size. As example:

    - Ellipsoidals (Source 4) all focusing in the same upstage or downstage direction can often be hung 1'3" center to center.

    - Units whose beams cross shoot across the stage at 45 degree angles to each other, might need 1'-6"

    - Ellipsoidals focusing as a cross stage shot from the end of the truss or electric, might need 2' center to center. Zoom ellipsoidals such as an Altman 15-35 Shakespeare zoom, might need more room.

    - PAR64's on trusses are often pre-rigged on 6 lamp bars that have 1'3" spacing, center to center, as they are generally all focusing in the same general direction.

    - 5kw fresnels, or other similar beasts, as used by a film/TV shoot or on an Opera, would need spacing of 3ft., or whatever.

    - Moving (head) lights are very particular, and often need 2'9" spacing in order for the head to have free range of focus.

    The lighting designer needs to know about instrument spacing issues and will draft the lighting plot with spacing indicated to allow the instruments to focus to the desired location, thus the light plot will have the lighting symbols drawn and spaced to scale to eliminate spacing issues. One thing you might see on a plot, is a note adjacent to the instruments on a position for the first instrument to be 1'6" stage left of center line, and a second note for all other instruments on that position to repeat that spacing, as example. You then might see a note that say's "reverse and repeat", meaning everything on stage right is a mirror of stage left.

    Which reminds me of an LD who used to do touring advance light plots and who would repeatedly specify 40 - 8" fresnels to be hung on a 50ft. pipe. NOT.

    Steve B.
     
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  3. Van

    Van CBMod CB Mods Premium Member

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    Well, Let me exp-lain this from a Wood Butchers perspective then we can extrapolate to Sparkies POV.
    Let's say you are building a 4' by 8' platform and you are framing it with 2"x4". You have the end pieces, rails and the long sides, stiles and the toggles the short pieces in the middle of the platform. If the plans call for the toggles to be placed 18" OC < on Center> then you, make your outside frame. Starting at one end < rail> Measure from the outside, left hand side towards the right you would make a tick mark at every 18" increment, so 18, 36, etc etc. Now the trick to making the layout OC is that you need to go back to your tic marks and make compensation marks. A 2x4 is 1 1/2" wide < when used as framing> you want that 1 1/2" to be centered on the mark. so go to your first tick mark measure backwards or forwards... how much ? right 3/4". that's half of 1.5". Now you line up the outside of the board with the compensating tick mark and you are 18" O.C.. Same thing with lights except you just place the raised area in the middle of the C-clamp, right on your layout mark. < you do chalk the layout of your plot right ?> The important thing to remember when doing OC layouts, in carpentry is to always start on the outside edge of whatever you are measuring. If you don't your seams will not work out properly. Hope that helped.
     
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  4. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Only riggers possess the mental aptitude necessary to play with chalk on the sidewalk...Tall Paul. Lighting people now use hang tapes.
     
  5. rmarston

    rmarston Member

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    So - The light plot is the LD's drawing decribing the instrument placement, and all the other attributes that describe how this instrument will be used and connected, and patched, etc, etc. These instruments are drawn on trusses or pipes to show where they are to be hung. There is also an elevation view showing height from the stage floor, with this view, the instruments can be located in 3 dimensions.
    Spacing of the instruments on center is the distance between two instruments measured from the center of C clamp to the center of C clamp. For example - hang two ER's on center, 1'6" apart.
     
  6. TupeloTechie

    TupeloTechie Active Member

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    Ok, so I think I'm starting to understand this better, but just a couple more questions, mainly dealing with the light plot:

    ~I have seen many plots that say something to the line of "all fixtures spaced 1'-6" on center unless otherwise noted," what if I have a large gap between lights on a hanging position (like maybe 5 feet or so,) or even if they are 6"Fresnels but I have them spaced 3", not 1'-6", how do I note this?

    ~Say I have two lights that are to be aimed in the same way, such as strait down, and I have them spaced so that the yokes of each light are touching each other(so essentially like 6" spacing), how would I go about putting this in a plot if all the spacing is 1'-6"?

    I think I'm making this too hard on myself...
     
  7. Van

    Van CBMod CB Mods Premium Member

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    Well if your LD has two fixtures planted on 3" centers, the only way you are going to be able to hang them if if you forward yoke one and back yoke the other.
     
  8. SteveB

    SteveB Well-Known Member

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    "I have seen many plots that say something to the line of "all fixtures spaced 1'-6" on center unless otherwise noted," what if I have a large gap between lights on a hanging position (like maybe 5 feet or so,) or even if they are 6"Fresnels but I have them spaced 3", not 1'-6", how do I note this?"

    I've attached a quickie light plot I did up for a recent rental. It shows typical lines and arrows drawn to indicate spacing for units just L & R of C/L, then spacing for all other units. , for those on the #1,2 & 3 Electrics. All other positions were pre-hung.


    "~Say I have two lights that are to be aimed in the same way, such as strait down, and I have them spaced so that the yokes of each light are touching each other(so essentially like 6" spacing), how would I go about putting this in a plot if all the spacing is 1'-6"?"

    If you go to the websites for the assorted manufacturers, you will find download-able spec. sheets for most lighting gear, including measurements for the fixtures. The old-style hand drafting templates sold by Field Associates, as well as the assorted fixtures built in to the libraries of the assorted CAD programs (AuroCad/LD Assistant, Vectorworks, WYSIWYG) all have their instruments with correct dimensions.

    Thus, as you draft a plot you can see as you place symbols on the drawing, when you will run into conflicts. The assorted "1'3", 1'6", 2'" spacing guidelines are just that - guidlines and a good electrician will adjust as required when hanging. Which makes it all the more important to fit as much information on to the plot as needed, to make the electricians job less a guessing game.

    "I think I'm making this too hard on myself..."

    Nope. Good questions

    Steve Bailey
     
    Last edited: Sep 8, 2008
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  9. soundman

    soundman Well-Known Member

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    I am going to read this as 3'. Attached is a copy of a plot from a designer who has made a symbol in vectorworks that has tick marks every 18". My guess is that he creates this for every venue he works in so it is the correct length. Anyway he lays it over the pipe and that allows anyone at a glance to read the spacing. Another way to draft this would be to use the align and distribute tool, but thats drafting stuff.
     

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  10. jwl868

    jwl868 Active Member

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    The use of the “on center” reference makes the locations of the lights (or any point) specific, especially when used with an ambiguous term such as “spacing”. This distinguishes it from other terms/reference points used to describe spacing, such as “edge”, “end”, or “face” (example: 1’ face-to-face), though in the post’s examples, “on center” is the most practical for many reasons.

    Joe
     

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