My lights arrived and I wanted to report on how things worked out.
I set up a corner section of my booth and hung 3 canvas prints. A 20"x24" print was hung 2" from the top. A 20"x28" print was hung 20" from the bottom and a 14"x20" print was positioned in between these two. They were all in landscape orientation, and the three prints comfortably filled most of the 2.5'x7' section. More specifically, I had planned to use ~5' of the vertical, and that is how I positioned the prints.
I took measurements on all four sides of each print (midway on the side) and in the centre. The ambient light level in the room was 184 lux. The brightest point was the bottom of the top print without diffusion and the center of the top print with diffusion. It measured 905 lux without diffusion and 520 with diffusion. I had estimated that I would get 753 lux (70 fc) without diffusion and 377 lux (35 fc) with diffusion. I've done better, and the difference seems to be the 20% reduction I applied to account for inefficiencies. That factor was not required, and removing it virtually brings the numbers into alignment (theoretical versus measured). That's cool.
Shifting to light coverage now. Without diffusion the light levels across the top print varied by 1.6 EV. The second print varied by 0.7 EV and third by 1.1 EV. Note that the second print was smaller and yes, I realize it would have been more balanced to have used sample points spread evenly across the panel. However, I wanted to test a real-world scenario.
With diffusion the light levels across the top print varied by 0.6 EV. The second print varied by 0.8 EV. The third print varied by 0.8 EV.
I much preferred the diffused lighting. It was more even and more pleasant to look at. Giving up some light level was well worth it. In fact, the prints looked "just right". Not too bright and not too dark, almost as if they weren't even lit. You could of course see the difference when switching the lights off and on, and the kind of "pop" they added. Conversely, with no diffusion you knew they were lit, as the light was harsher and you could see the brighter area where the bulb was aimed.
I did one last experiment. I turned off the overhead florescent lights to see how the prints would look when the ambient light was significantly reduced. This was a boardroom with windows on one side, and it became noticeably dim but not dark. Unfortunately I didn't think to measure the ambient light. In this light the prints looked somewhat under-lit. This is of course subjective, and without the a-b comparison, and with some time for my eyes to adjust, I might have formed a different opinion. The room was likely close to subdued museum lighting. However, I want the prints to have an impact (i.e. marketing) and the first environment I will be in has an ambient light level of only 50 lux. So, I will be adding some fixtures to increase the overall level. The way my light bars are positioned allows me to mount fixtures further away to get the wider coverage I need for this.
I am very pleased with how things turned out. The methodology used to integrate two sets of data, and the general math behind all of this, worked well. Most importantly, the prints look great under these lights.
Thank you again to everyone who helped me work through this. I hope this information is useful to someone else down the road.
Terry.
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I am planning to order track lighting with one Solux 3500K, 50W, 36 degree MR 16 bulb for each 2.5' section of my display. I would like to light approximately 5' of the 7' panel vertically, with the top 1/2 or so being the most important. The booth is 7.5' wide by 5' deep.
My light bar sits 15" above the top of the booth and I plan to set it so the track lighting is 36" away. If I shine the bulb at a point 21" down from the top of the panel (36" vertically down from the track lighting) the light will be 51" away from the print, and it will be shining at a 45 degree angle. When I look at a generic photometrics chart, take into account differences from the Solux bulb, and factor in bulb/transformer inefficiencies, I get a light level of ~70fc and a beam spread of ~2.7' across by ~4.4' vertically. If I diffuse the bulb the light level goes down to ~35fc.
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It will of course be interesting to see how this actually works out in real life. My concern now is to prove out my basic approach, and to make sure I'm in the ballpark before I move forward.
