Strip Club Physics I was sitting in my home stripclub (Ten's in Tucson), tired, enjoying a quite moment (neglecting the pounding music) and took my glasses off to rub my eyes. Reaching for them I realized that my perfectly clear lenses were casting a shadow on the flourescent pink flyer that was sitting on the table. So strange, to see clear glass throw a deep shadow. The flyer was fluorescing in the UV light from the "black lights" in the club. The clear lenses were coated to block UV. I paid extra for that UV coating so I was glad for that empirical evidence that the coating was working. I had my camera with me so as an experiment I removed my "Sky Light" filter - that $6 piece of glass every camera dealer talks you into buying - and held it to the glowing paper. Dark shadow. Hum, maybe that thing does something after all. Then, as a reality check, I removed the camera's lens and tested it, same deal, camera glass is already opaque to UV light. Damn. While I was experimenting Miranda walked over and asked what was up. I proceeded to explain my recent findings. She listened till the end of the current song, then immediately asked if I'd like a dance. I took the dance, but I was still thinking about strip club physics. Black Lights Black light refers to Ultra Violet (UV) light, light beyond the visible blue part of the spectrum. The black lights in strip clubs are basically conventional flourescent lights with the phosphors removed and a deep blue filter added. Ionized mercury vapor in the tubes emits a wide ranging spectrum, including UV. The blue filter absorbs almost everything except for the UV. Most strip clubs are absolutely suffused with invisible UV light. My jeans and white t-shirt were glowing bright blue-white too. This is because of... Blueing ...the flourescent dye added to detergent (extra in Fresh Start) to counteract the normal yellowing over time of natural fabrics. When the UV of sun light hits the dye it fluoresces blue. In the additive colors (not the finger paints they gave you in kindergarten, those are subtractive) yellow plus blue yields white. I like wearing a white t-shirt that's been washed in Fresh Start detergent to strip clubs because it will glow so brightly that it illuminates the coochie of whoever is dancing for me. I could see where Miranda stopped shaving, and where she started again. Nice. Just about then, with a hiss, a cloud of... Smoke ...blew across the stage. This isn't really a smoke. Smoke is defined as a suspended emulsion of a solid in a gas, like smoke from a cigaret. There are emulsions of all possible pairings of states of matter (gas in liquid (mouse), solid in gas (smoke), etc.) except gas in gas. What was blowing across the stage was a fog, a suspended emulsion of liquid in gas. The liquid is, according to it's Material Safety Data Sheet (http://www.coolstuffcheap.com/lib/coolstuff/amerfog.pdf), 10-30% Propylene Glycol and 30-60% Glycerine. Essentially the same formula as sex lube. The smoke machine sprays the liquid across a hot electric element and then a fan blows the resulting fog across the room. The droplets are so small that the random Brownian motion of the air molecules keeps them suspended indefinitely. Eventually most of the material evaporates, while the rest contributes to stage crud. After the dance Miranda asked if I'd take her picture. Beaming, I grabbed my camera and snapped the shot. Later I would be disappointed by the poor contrast of the image, which would make me think of... Fog Optics I hate shooting pictures in a foggy strip club because the contrast is always much worse than what you see with your eyes. Angle of incidence equals angle of reflectance. The flash on a camera is generally very close to the axis of the lens. When the blast of light goes out, a great deal of it ends up reflecting off of the fog droplets and directly back into the lens, washing out the intended subject. As a passive audience member (no headlights on your head) you don't see this because most lights are set at great angles from the axis of your eyes. That's why the fog lights on a car are set so low, to increase the angle of the beam from the axis of the driver's eyes. But now the lights were dimming, the volume and bass were coming up, and there was another blast of fog across the stage. I recalled that the reason I was there was to shoot a contest, and the first contestant was on her way out. I excused myself from Miranda and hustled to a side stage where I could shoot without being in anyone's way or being seen in the mirrors behind the stage. Lately Ten's has been remodeled and there is a ton of silvered glass at the back of the stage. Towards the central stage entrance the mirrors form a stair-step pattern with 6 inch strips set at 90 degree angles. The music and lighting became even more dramatic, and the dancer strutted out. I fired a shot before the next blast of fog could hit - and actually _saw_ the reflection off of the stair-step strips! Angle of incidence no longer equals angle of reflectance. God damn... Corner Cubes! If you take a square box and lop off one corner, that corner is referred to as a corner cube. Three plains all meeting at 90 degrees. If those three plains are mirrors then you have a construct with the unusual property that it reflects all incoming light directly back to it's source. Don't believe me? Throw a rubber ball at the upper corner of a room (doesn't work for rooms with vaulted ceilings) and it will always bounce right back at you. That stair-step mirror pattern on stage wasn't a true corner cube because it only had two plains, but so long as I was shooting level (normal to the plains) it had the same effect. Every shot that had any part of the 90 degree mirrors in it got a blast of light right back. Upon developing what you saw was the silhouette of a dancer, plus the brilliant white star of a xenon flash to one side or the other. Of course the xenon flash wasn't truly white. That illusion results from the inability of our eyes (and film!) to distinguish narrow bands of color in the light. If you were to pass the light of a camera flash through a prism you would see that the... Xenon Spectrum ...is actually made out of a series of very narrow bands extending across the whole of the visible spectrum and well into the Infra Red and Ultra Violet ends. It so happens that the average of all these peaks looks to us to be pure white. This can bite you if you're shooting a bride under xenon studio lights (yes I shoot weddings too). Unless you filter your lights for UV it is quite likely that the white gown will come out blue on the prints. This is because of... Blueing ...in the dress, which is.... Did anyone actually make it this far? If so, have a nice AFTSK! Marc -- "What we have here is a failure to assimilate." --Cool Hand Locutus http://www.tucson-topless.net Uncovering Tucson and Baja Arizona http://tens-showclub.com Tucson's Ultimate Showclub