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50 Lumens

Discussion in 'Lighting and Electrics' started by Charc, Jul 21, 2007.

  1. Charc

    Charc Well-Known Member

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    I've read, from multiple sources, multiple times, that 50 lumens is considered to be the lowest level of usable light for stage lighting. I've never obtained a definition for "usable light". Is that quite dim light, but provides a clear view of the subject? Or does that mean something that might be useful for accent or something, but not enough illumination to provide a clear view of the subject? I'm not quite clear on that. And let's say I have 100 lumens of light, but I gel the light with a filter that has a 50% transmission. That means I have 50 lumens on stage, or the lowest amount of "usable" light?

    What is the lowest amount of IR light? Somewhere on here was a discussion of using WFL PAR64s, with deeply saturated blue color filter run at like 5-10% as a source for an IR camera. Is this truly enough light, or was this a hypothesis?
     
  2. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    I don't have the exact answer to your question. You can somewhat accurately think of I.R. as the heat escaping the lamp... yeah there's more to it than that, but a large part of the heat you feel is really IR. Something that only produces 50 lumens is going to be very dim... but it's still generating a lot of heat... and a lot of IR.

    Also I believe you should be using some extra dark Red Gel, not Blue. I believe at the high end of the spectrum there is some cross over between Red and IR. Blue Gel would potentially block those "near IR" wave from getting through.

    How am I doing? Anybody?
     
  3. Charc

    Charc Well-Known Member

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    Good call on the red, yes it is closer to IR. I think the idea though was that color filters are designed to let as much heat through as possible, so as not to burn out. This means that the difference between deeply saturated blue and deeply saturated red would be negligible, so since blue (I would think) would be harder for the audience to pick out, you can run it at a higher intensity, getting more IR light, without having the light noticed by the audience. Though all of the preceding was a guess.
     
  4. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Somewhere in the thread I started a couple months back about a night vision camera, I think I remember someone saying they ran a PAR with double red gel at about 5% or 10% and that was all the light they needed for their IR camera.
     
  5. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Another more expensive option is to get a "cold mirror". A dichroic filter which reflects visible light and allows IR to pass through. I looked into those and if I remember right they run in the $50-$100 range.
     
  6. Footer

    Footer Senior Team Senior Team Premium Member

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    Also called "woods glass". If you get enough of them, they give a pretty good black light affect, if you have just one full stage, you might get spikes to glow a bit, but nothing insane.
     
  7. Charc

    Charc Well-Known Member

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    I thought blacklight effects came from UV light?
     
  8. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Yeah Footer wrong end of the spectrum buddy... get some rest. "Wood's glass" is a filter that allows UV to pass while blocking visible light. While a "cold mirror" allows IR to pass while blocking visible light (it's what they use in Selecons to cool the light down). But as he said there's a big difference. It takes a TON of incandescent light source to generate a small amount of UV. Where it only takes a small incandescent source to create a lot of IR. As we've all heard lately in the news, Incandescence is really inefficient and ton's of excess heat is wasted in the production of light. Gaseous discharge lamps on the other hand are much more efficient and are sort of tuned to a specific wave length. So it's easy to produce a ton of UV with a discharge lamp while it's harder to produce IR.
     
  9. Charc

    Charc Well-Known Member

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    My understanding is that the "cold mirror" technology is in source fours as well.
     
  10. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Yes the reflector in a Source4 is a cold mirror. It reflects visible light forward into the gate while allowing IR to pass through the reflector and into the body of the S4. However the 30% or so of the light moving directly into the gate without hitting the reflector does not get filtered so quite a bit of heat is retainted. That's one of the things that makes a Selecon so COOL (pun intended). Selecon's are banana shaped with the lamp and reflector pointing up. At about the point where the gate would be on a S4, it hits the cold mirror which is sitting on a 45 degree angle. The IR passes straight out the top into a heat sink while visible light is reflected forward into the lens tube. It makes them run much cooler up front.
     
  11. JD

    JD Well-Known Member

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    OK, here are your answers. First, I am going to address the IR question. A blue gel sounds counterintuitive for an IR filter, but it isn't!! The dark blue gels have a pretty good IR pass on them, as IR is one octave away frequency wise from blue. Also, it's the only way they would survive without heat blowing out the color medium. So, you set your lamp on a dim setting where the filament is putting out 90% IR and block the visible red light with the blue gel that is allowing the IR to pass. Instant IR source! If you are using a cheap IR security camera, you will be surprised at how good the results are! (see PS below)

    As for the light question, it depends on what ambient light you are working with in the theater. The human eye has a 100,000 to 1 ratio between washout and black. (It does have to adjust a bit.) (btw- Film is about 1000 to 1) The eye also has a really great "automatic gain control!" So, if your theater gets black enough, you could probably do stage lighting with candles. (after a few hours.) HOWEVER, we live in the real world, with bright little EXIT signs over the doors, light leaking through doorframes, etc. So, how far do you have to get above the ambient light to "light" a show? More on the eye- The eye has a wide range, but as with sound, level changes have to be pretty radical to be noticeable. Except for effect lighting, your stage lighting level needs to be about 10 times as bright as the ambient light in the theater. The exception to this is color. A deep red filter may knock much of the transmitted light out, but the monochromic (I know, most colors are not) light has steep peaks which the eye can discern better than a "flat" light of the same lower output.

    All this technical jumbo aside, the only real rule to follow is to sit back, watch the show at a dress rehearsal, and follow your heart!

    PS: I once knew a guy that worked out a IR filter for his follow spot and used a sniper-scope for his blind pickups!
     
  12. Grog12

    Grog12 CBMod CB Mods Premium Member

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    I've lit entire scenes in 600 seat houses with nothing but matches...here's the trick you have to pull down slowly...really slowly over the course of 10-15 minutes. The eye adjusts qucikly but if you can help it that's great.

    Secondly the show has to call for it. The show in question was Wait Until Dark...which obviously has a scene lit by matches...we chose to use no reinforcment to light it. It worked nicely...but we had to kill much more than just the stage lights. The aisle lights were doused...the moving lights were lamped off...The Unisen panel was covered.
    We would have turned out the exit lights or had covered them if we had enough crew standing by to pull the coverings in case of emergency but we didn't and the red wasn't as distracting from the match light.
     
  13. ship

    ship Senior Team Emeritus Premium Member

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    Very great replies so far, don't think I can add anything beyond this. Candle power, a question of what you started at first before what you can go to in seeing. Much in the olden days, now how did Caspar Neiher light his talent with a radial Leko sufficiently? (Did he also do lighting or just amazing golden age sets, and who was doing the lighting for him if not? One of the books - his auto biography I didn't yet read.)

    This much less I'm fascinated with the concept of the Selcon heat dissipation design theory by way of going back to a radial concept in general. Never knew this in concept.
     
  14. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Selicon isn't a radial/non-axial even though it looks like it is. The lamp sits in the same position within the reflector as a typical S4 or Altman instrument. Remeber that in a radial/non-axial the lamp sits at an agle to the back of the reflector. In a Pacific it doesn't.

    Here's a link

    http://www.seleconlight.com/index.p...gory_id=19&option=com_virtuemart&Itemid=119-4

    If you go to the instruction manual (http://www.seleconlight.com/files/english/opmanuals/Pacific opmanual excl 513.pdf) You find that theres a diochroic mirror there which reflects the light to the gate while letting the hot part of the spectrum out the back grill.

    I'd search for an online example of a radially/non-axial instrument..but I'm tired. If you have an older Parker and wolf there's a section in there.
     
  15. JD

    JD Well-Known Member

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    Here's an interesting light plot for a show that uses hundreds of fixtures, but only has a 4 lumen average light level. Millions of people have seen the show, you may have too! Look at the lamp key and count the lekos... wow... Recognize it yet? It's the haunted mansion at Disney World.

    You can do wonders in the dark! It's all about tricking the eye.

    Let me add credit for that plot. (Heard about it from a employee.. er Cast Member.) A Disney endorsed site called http://www.doombuggies.com/
     
    Last edited: Aug 30, 2008
  16. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Yeah ship the cool thing about the Selecon is that it looks non-axial and takes huge advantage of that bend for heat removal... but it isn't actually non-axial. They cheat by putting a mirror at a 45 degree angle about where the second focal point of the ellipse should be. They are really fun to play with... gonna buy a dozen for my theater primarily for pattern projection... plus you can print a color transparency on you printer and slide it in there without the Rosco Image-pro fan unit. It runs THAT cool.

    For the rest of you Charc and I have been chatting a lot about IR and night vision cameras in P.M. That's sort of what started this thread. I think the interesting question is how much IR is still coming out if you have your instrument turned way down to just 5% or so. Due to the inefficiency of incandescence, even though there is very little visible light, there is still a ton of IR coming out.
     
  17. Logos

    Logos Well-Known Member

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    Hey Gaff: I was talking to a tech from one of our big theatres here in Adelaide and while he loves the Selecon he says leave it in place try not to move it around. They keep really good records of lamp usage by each fixture and the lamp usage goes up in a light that is shifted often by a pretty large factor. This is hearsay of course and it may only apply to the 240v version in Aus/NZ. For what it's worth.
     
  18. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Interesting. Although as you say it's going to be a totally different lamp here. I'm planning on buying about a dozen of them for my new theater primarily for gobos and home made transparencies. I'll have to keep track of them a bit and see if it's a problem. I'll tell you what happens in a year or so.
     
  19. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Most lamps have issues with to much jiggle...especially if they're hot. You wouldn't think that the 240v version would be too much off the 120v version...but stranger things have happened....granted the filiments probably just a little different which would make me think the 120's would break even easier.
     
  20. icewolf08

    icewolf08 CBMod CB Mods

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    I have used a 90˚ Selecon with a primary and it's opposite secondary color gel in front as an IR illuminator for IR video. It is amazingly effective, which I think goes to show that there is still a significant amount of IR energy that doesn't get filtered out by reflector and mirror in the Pacific. The useful thing is that enough gets filtered out to not instantly burn the gels.

    By the same token, it has been my experience that IR cameras, especially the B&W ones that I have worked with, don't require too much IR energy to produce a clear image. At my theatre now, we don't use any additional IR illumination other than the LEDs on the camera, and in a true blacout you get a pretty good image. It can pick up light on stage that is barely (if at all) visible to the eye.

    So, my point, well it seems that you don't need too much IR energy to work with an IR camera. I also have to assume that if you wanted to create an IR illuminator with a Source 4 or other unit not a Pacific, you would end up with way more IR energy and probably could get away with running it at a much lower level.
     

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