Illuminance in practice

[John Godfrey]

Hi.
I am trying to decide on a 50 deg Colorsource spot, and a 70 deg to replace our Force 4 instruments. our Procoeniun is 30' wide, and our FOH bars are 6', and 12'. We have a throw of about 15'. We only have 10 F4 50 deg and 5 old strand pattern profile spots to fill in the dark spots.
I have looked at the photometrics for the 50 deg and 70 deg spots
https://www.etcconnect.com/WorkArea/DownloadAsset.aspx?id=10737484687
and see the 50% lux for the 50 deg has a wider spread than the 70 deg. I gues this means I would have to overlap the fields more. I presume that if I use a frost gel, this would help.
I have no idea how much illuminance is needed for a production. The 50 deg has 64 fc, the 70 deg 40 fc. How do these translate to acceptable onstage lighting?
I am wondering if I go with the 50 deg, I may need 4 light pools downstage, 8 instruments, but If I go with the 70 deg, I could get away with three, and 6 instruments.
Any suggestions?
Thanks,
John

 

[icewolf08]

Typically people try to use fixtures that create a 10' wide pool of light and often on the order of 100fc. It is also typical to plan for an odd number of areas so that you end up with an area on the center line of the stage. Of course you always want to overlap your areas so that the light blends nicely and you get even illumination. In your case, I certainly wouldn't go wider than a 50 degree unit, but I would actually probably consider a 36 degree and just getting a few more of them.

In the department of what its worth, it is a Source 4, not a Force 4. Named such for the 4-filament geometry of the HPL lamp.

 

[BillConnerFASTC]

Alex offers good and tested advice and it would serve you well.

On the other hand, and with all due respect, I did think about this when I read it yesterday.

The level is hard to pin down and has a lot to do with "design". It's also affected by distance to most distant audience member, and you gave no clue to that. I like 200-250 foot candles from a follow spot but I know color media - a gel - will cut that fast. Deep blue is somewhere around 5% transmission, so next to nothing. In a tungsten halogen world 100 fc might not be a bad goal but I find LED is changes that with its additive mixing. The best answer would be if you put one light on a dimmer and asked a small group to judge what was enough. I'm guessing there are a lot of scenes played in 5 fc, but somewhere in the 25 fc range - in clear or no color - would be satisfactory for a several hundred seat space. I'd probably roughly aim for 50 fc in clear with LED

I'm not a huge McCandless method proponent - the left and right, warm and cool, system of two lights into each area. But the idea of reveal form is important. You can do that with a straight on wash and box booms or sides; or my choice of implosion/explosion of warm or cool from the center and the other from the sides. (You may not be able to do that if you only have battens left and right, not center - I didn't understand that

our FOH bars are 6', and 12'

Three or five was my first thought for the reason Alex proposes - that often you want to highlight center. (Ive done the implosion/explosion often with 3 or 5 from center and 4 or 6 form sides (2 or 3 each side).

In 30' - you might get away with 3 areas in a McCandless system - just 6 lights . The problem can be the blending and the dramatic angle shift as a performer moves across the stage. Diagram it and see if that makes sense.

Please let us know what you do and how it works out.

 

[RickR]

How much is bright? I worked years only briefly hearing that film requires +100fc. Nobody outside of film/TV carried a light meter, and even now I rarely see one. Then I spent years in architectural lighting where everyone worried about brightness and evenness. Here in WA health inspectors in schools carry meters and will write the building a ticket. ButmMany places are far darker than recommended.

Many stages, especially small schools and community theaters call 50fc bright. A light at full that creates 100fc will blend with others so that they all add together. You can easily get 200-400fc that way. But then color and dimming take a big bight out of that. In LED a deep color means 1/3 to 1/7th of the emitters are on. Brightness falls off quickly.

Lighting is about contrast as the human eye adapts to a wide range. Interestingly the distance to the back row of seats is the critical number. You need enough light so that those folks' eyes can pick up all the details.

I see that Bill is saying much the same thing as I write this. I will also suggest a narrower lens, maybe even a 26. More fixtures also equals greater area control.

 

[BillConnerFASTC]

Area control is one of those things that I certainly learned and have used, but I wonder if in many theaters it's used much, in particular school and small community spaces. Just a thought of priorities.

 

[MNicolai]

Looking at this from a little different perspective than has been brought up yet...

I'm not sure how happy you'll be going LED with 70's. The emitter configuration in the light source becomes less coherent at wider angles. For such wide angles, unless you absolutely need shutters, you may be better served with wash fixtures. In that same vein, I expect you will not be happy with the sharpness of gobos. Gobos in 70's and 90's are already fighting an uphill battle for sharpness through the optics -- on an LED fixture because you also have to worry about color coherence, so you will see colored fringing on the edges of your gobo patterns and the patterns can appear soft.

As for going with 50's and dropping frost filters in, not only will you lose control of your light spill if that diffusion is too heavy, but whether you do that or go with 70's, your pools of light will be so sizable and lacking in directivity, brightness, and visual perspective that your lighting will yield an overall feeling of blandness. This is basically broadcast TV is lit, where shadows are the enemy and they almost always want to create visuals with no identifiable sources of light upon the scene. That tends to be the exact opposite of how theater is lit.

If you take it to the extreme and use a 90 as an example. Hang a 90 in an upstage corner of your plot and aim it cover a hefty chunk of your stage. Depending on where the actor stands, that's either a side light, a front light, a back light, or a down light upon them. Put 4 actors on the stage and it's all of those choices at the same time -- dimly. Mix it with a couple dozen other wide-angle fixtures from other directions over the acting space and there's no way to light the stage consistently except to light it in one color. Going all wide angle all the time forfeits your ability to exercise any meaningful artistic discretion and you might as well be lighting the stage just with fresnels flooded out.

If the driving factor for fewer fixtures is price, I would seriously consider getting more Colorsource PAR's (Deep Blue), and get only a couple CS Spots or even standard S4's for specials. It will give you more bang for the buck and allow you buy more fixtures. Alternatively, if you have the money, I suspect 36's will generally provide a better visual impact than an smaller array of 50's or 70's.