top-cat Posted October 22, 2014 Share Posted October 22, 2014 In the general "what happens if the building is on fire!?" sense that used to be trotted out fairly often as a reason why SpanSets shouldn't be used, I agree completely. My thought on this (which is I assume what you're saying) then the main danger to life is going to be the fact that the building is so engulfed in flames they they are reaching the roof... anyone in it is going to be dead whether or not a truss lands on their head. That post (which I'm still taking with a big pinch of salt) skates straight over the issue of the chain bag itself and on to SpanSets. A chain spill is not a trivial event, and I don't see any proposal to replace the chain bag with a steel box (thank goodness), so if this is a genuine issue then care with the lights is called for regardless of how the truss is slung. 100% agree. You don't find pyro guys saying "I'll send flames wherever I bloody well like", or laser guys saying "I'll shine my lasers into the audience, what right have you got to tell me where I'll shine my lasers?" So the lampies have no real grounds to ever say it. If it's going to be the case that the new breed of movers can produce beams so intense that they cause risk to lifting equipment, then programmers will simply have to adjust their workflow to ensure that lifting equipment is not at the end of their focusses for anything more than a flash. My fear is you'll get people saying "but it's OK because it's got a safety". I only say that because I've tried to point out to lampies that them lifting a truss with a spanset right behind an 8-way molefay could probably be done better only to be told "well it's got a safety on hasn't it?". Really not the point... By the by if a chain spill initiated at the top of the gaping hole pictured, that bag was too full - not big enough for the hoist it was attached to. That's something that gives cause for concern from time to time. Klein buckets being largely phased out and replaced with ARS (and ARS-style) bags oven the last few years has improved things greatly, but chain spills are still way too common. Agree about chain bags but too commonly you see motors out and about with chain bags too small. Was told by a corporate events rigger once (in a smug "look at me" kind of way) that he always substituted his chain bags for smaller ones because they looked less unsightly and there was nothing inherently wrong with a full chain bag. Sadly idiots like this roam the earth freely. Sadly I think many chain spills can be less attributed to the type of chain bag and more to user incompetence, and the number of people who frequently use electric hoists who still don't know how to pack a chain bag properly. Don't think I will ever stop seeing guys just dumping the chain into the bag at random rather than feeding it in from the dead end, blissfully unaware of the consequences. "but it's quicker!" http://www.blue-room.org.uk/public/style_emoticons/default/blink.gif Link to comment Share on other sites More sharing options...
bigclive Posted October 22, 2014 Share Posted October 22, 2014 Well we did a scientific experiment involving a conventional Sharpy and a marshmallow (the Sharpy is out of sight in this picture) and it failed to even melt the mallow, let alone toast it. It is a bit of an issue though, since a Sharpy can end up pointing at an adjacent light for a while during programming of others in the same cue. Link to comment Share on other sites More sharing options...
Bryson Posted October 22, 2014 Share Posted October 22, 2014 I knew Clive would come through on testing this for real. Clive: you are our Production Industry Mythbuster. Now, can you get your hands on a Tallescope....? ;) Link to comment Share on other sites More sharing options...
Seano Posted October 22, 2014 Share Posted October 22, 2014 Good to see protective eyewear in use there Clive, safety first. :) My first encounter with Sharpys was at rehearsals prior to a British rapper's first 'proper' UK tour. I read with interest the "nothing within 12m or this fixture with burn it with fire!" warning label (or whatever it actually says), and later in the day watched as the star of the show (a large black gentleman with a bald head) sat on a bar stool centre stage and the LD meticulously focussed every Sharpy in the rig onto the back, sides and top of his head. Unusually patient and easy-going sort of a chap as rappers go. There was a bead or two of perspiration, but definitely no smouldering. Link to comment Share on other sites More sharing options...
Dj Dunc Posted October 23, 2014 Share Posted October 23, 2014 I've tested an SR Beam at 2m onto thick office carpet tiles and had a hole through it in less than five minutes. Certainly worth considering for those smaller corporate jobs where you have carpet stage below. Link to comment Share on other sites More sharing options...
the kid Posted October 23, 2014 Share Posted October 23, 2014 I would imagine it is also how it is focused and that sweet spot. I also kinda wonder the real v's fake ones. I did a gig last week that had some very good other brand "not sharpies" I imagine their, mallow melting ability is far less than a real one. Link to comment Share on other sites More sharing options...
top-cat Posted October 23, 2014 Share Posted October 23, 2014 I would imagine it is also how it is focused and that sweet spot. I also kinda wonder the real v's fake ones. I did a gig last week that had some very good other brand "not sharpies" I imagine their, mallow melting ability is far less than a real one. not necessarily? it's an act of physics. light shined through a lens, get's brighter. Doesn't have to have a CP badge on it to obey the laws of physics... Link to comment Share on other sites More sharing options...
Shez Posted October 23, 2014 Share Posted October 23, 2014 it's an act of physics. light shined through a lens, get's brighter. Doesn't have to have a CP badge on it to obey the laws of physics...I think you're trampling all over the laws of physics here. Light shone through a convergent lens can become a more concentrated, narrower beam but it can't get brighter - there's no way of magically producing more light out of nowhere. Link to comment Share on other sites More sharing options...
the kid Posted October 23, 2014 Share Posted October 23, 2014 I was simply thinking that it has been noted that the quality of light in fakes is sometimes not that great, the alignment of lamps v's reflectors v's lenses. I am sure with some thing more washy it is not noticed, but if you are doing a comparison I personally would hazard a fake would perhaps not be quite as focused. Link to comment Share on other sites More sharing options...
top-cat Posted October 23, 2014 Share Posted October 23, 2014 it's an act of physics. light shined through a lens, get's brighter. Doesn't have to have a CP badge on it to obey the laws of physics...I think you're trampling all over the laws of physics here. Light shone through a convergent lens can become a more concentrated, narrower beam but it can't get brighter - there's no way of magically producing more light out of nowhere. sorry bad choice of words and you are right to critique! choice of words should have been that lens allows the beam to be very bright because of lack of wastage outside the main beam and the fact it's all focussed into a small area. but the laws of physics are such that an identical lens from another manufacturer with an identical lamp would have much the same effect. and indeed there are some manufacturers who've chosen to use even brighter lamps in their beam lights... Elation did one with the 15R 300W lamp in, and Chauvet did one with a 230W discharge lamp. Link to comment Share on other sites More sharing options...
Brian Posted October 23, 2014 Share Posted October 23, 2014 Although light, as in the visible stuff, isn't the issue here. It'll be the IR in the beam. Link to comment Share on other sites More sharing options...
timsabre Posted October 23, 2014 Share Posted October 23, 2014 Although light, as in the visible stuff, isn't the issue here. It'll be the IR in the beam. This is an interesting thing, surely the absorption of any wavelength of light by an object would raise its temperature? It's not just IR that causes heating is it?They have some fairly chunky IR filters in moving heads to stop the gobos and dichroic filters cooking, though I presume some will still get through. Link to comment Share on other sites More sharing options...
Shez Posted October 23, 2014 Share Posted October 23, 2014 It's all electromagnetic radiation, just of different wavelengths. If you shine an LED torch at your hand, it will raise the temperature of your skin but by so small an amount that you'll never feel it (you can't destroy the energy - the light that isn't reflected has to go somewhere). I suspect it would be nigh on impossible to create an optical IR filter that left the red end of the visible spectrum completely untouched, hence some IR still making it out. Link to comment Share on other sites More sharing options...
Brian Posted October 23, 2014 Share Posted October 23, 2014 The Super Sharpy has a 470W lamp; that means the absolute maximum amount of power that can come out through the lens is 470W. It doesn't though because it's nowhere near 100% efficient. Instead we know that 23,000 lumens come out of the lens. Today's physics homework... 1) work out how much energy is within the beam.2) knowing 1), work out the temperature rise of a matt black object placed within the beam at a distance of 7m. Link to comment Share on other sites More sharing options...
Jevans Posted October 23, 2014 Share Posted October 23, 2014 Physics? I can do that! I would note that lumens are a unit that depend on the response of the eye, and so are not as useful in a physics context as, say, the bolometric flux, which is the actual power per area delivered over all wavelengths. However, if we assume that the lamp in a Super Sharpy is a blackbody at the temperature of the Sun (which it won't be, especially because of the IR filters, but it's a decent first approximation) then 93 lumens = 1 Watt. (The integration to get the conversion is a little boring as it relys on knowing the wavelength response curve of the eye, which there isn't an easy formula for, but there's a little summary here.) 23000 lumens therefore equals 247.3W of power in the beam. I'll assume that as the beam is very small and non-diverging so that no power is lost, which makes the distance irrelevant, and that our matt black chain bag/other object( which I will, of course, also approximate to be a black body) absorbs all of the power in the beam and that all of that energy goes into heating the body. For a stable temperature the input power will equal the heat flow out by cooling; for which I'll use Newton's Law of cooling which states that the rate of conductive cooling is equal to the temperature difference, multiplied by the area A, divided by the thickness of the material between the two temperatures w, multipled by something called the thermal conductivity, k. Unfortunately this coefficient is very difficult to find for any particular system except by experiment, but as a guess from data about 0.2 W/Km would be about right for most plastics, and let's guess at 2mm for the thickness of the chain bag, and a surface area of 0.5m^2. P = kA/w (Tbag-Tair ) Therefore Tbag = Tair + Pw/KA = 20 degrees + (247.3 * 0.002) / ( 0.2 * 0.5 ) = 25 degrees C So on the face of it this seems improbable - HOWEVER this assumes all the power was delivered magically evenly into the bag. If you had all of the power being delivered into a small area on the surface of the bag you could end up with a hotspot getting very hot indeed. Physics is of course an empirical science however... I don't have a Super Sharpy handy! :D Link to comment Share on other sites More sharing options...
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