Using ETC Source Four for Broadcast Lighting - Lamp Intensity vs. Color Temperature?

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Hey there, I am a long-time reader but first-time poster. Booyah! I contract at a large campus of a local church, and we are planning to re-hang our front light ETC Source Four ellipsoidals.

I am told that our goal color temperature on-stage 5600K. We are planning to use Full CTB gel to achieve this. However, I am also told that I should run ALL Source Four's at 100% intensity. This is supposedly for (2) reasons.
  1. The lamps last the longest at full intensity, not being dimmed, because that's "how they're designed to operate."
  2. If the lamps are dimmed below 100%, their color temperature will get much warmer than their rated 3200K, and therefore, 5600K is no longer reachable.
Are these two statement correct? Are there any graphs available that show color temperature vs. intensity of a Source Four HPL lamp?
I don't want to burn through lamps like crazy, and I also don't want to go through the hassle of now using neutral density (ND) filters to lower the illuminance on stage!

I have always focused on achieving the correct angles for front lighting, but when it comes to the actual illuminance (footcandles) on-stage, I just set the fixtures to whichever intensity yielded good visibility of the band both in the room and on camera. That could be 40% or 100% or 55%, or whatever I end up recording into the preset on the console. Is this wrong?​
 

derekleffew

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Are these two statement correct?
No.
Are there any graphs available that show color temperature vs. intensity of a Source Four HPL lamp?
Not a graph, but a formula:
coltemp/COLTEMP = (volts/VOLTS)^0.42

If one were so inclined, one could easily create a graph (or several) with the Excel worksheet attached.

N.B. For any given wattage, there are FOUR versions of HPL lamp (115v vs. 120v, and standard vs. Long-life), so it's good to know exactly which we're starting with.
 

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MNicolai

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1) Incorrect. Lamps last longer when dimmed. Running them below their rated voltage is common for budget-conscious venues because they won't fail as quickly. At least a few theaters I worked at configured their dimmer racks to max out at 95-97%. A minor intensity shift was worth getting some extra lamp life.

2) Yes, the color temp will get warmer as you lower the intensity. Not sure I would say 5600k is "unreachable" because you can always adjust the gel, but you will see a shift.

Sounds like you're working in a film/broadcast scenario where you're trying to make it look good for the camera. If that's the case, get with your camera operator and do a white balance test. So long as the white balance on stage is consistent over the course of the event, most cameras can dial into 3200k specifically and correct it so the recorded video doesn't look extra warm.

If the light being "too bright" is a big deal, you can generally buy the same color temp lamps at different wattages. 375/575/750, etc -- but it's probably easier just to play with the CTB gels in front of a camera until you find a happy medium. Most cameras will perform better with higher brightness though.

Overall, the human eye is very forgiving -- perception of color and brightness is all relative and a shift in brightness and can fool you into thinking the color temp shifted and vise versa. I wouldn't get too caught up in making it perfect 5600k for the human eye.
 

MRW Lights

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well... that's interesting and it depends.... those wiser than me in ANSI standards will be along soon, but sure there is something to be said about resistance and electrical theory, but in terms of effective lamp life I would consider it negligible in terms of dimming vs full when it comes to measurable lamp life.

as for #2.... "yes" a dimmed incandescent lamp typically experiences a red shift tinting it warmer. To me it sounds like you have more of a camera white balance issue than a lighting issue. You shouldn't be accomplishing color temperature by lighting alone as that's essentially relevant to the settings of the camera.... 5600 isn't a radical color temperature, but it's not being accomplished in the easiest or I can 100% guarantee the best looking way....
 

macsound

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I'd be interested if they're being so strict on the color temperature as a guide and then once the install is done they can relax a little more. Like shoot for the stars and don't tell anyone they can fall short until the end, otherwise you'll be aiming short.
Agreed that cameras can white balance at any color temperature and usually the reason they want theatrical lights to be at 5600 is because there's also going to be a handful of HMI or HID lights mixed in. Those are way hotter and easier to gel the lights designed for gel than the hot TV lights.
 

RickR

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The only reason for a 5600K target is that some other source is present. Windows, fluorescents, etc. If that's not true then press for a change. The gels will eat a large chunk of the output and costing real money. The gels will burn out fairly quickly too.

You can fine tune your brightness with 'neutral density' gels. Basically shades of gray. For longer term use metal screens are far more durable. Both can be stacked in a light for precision control. All pretty common in photography.
 

macsound

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The only reason for a 5600K target is that some other source is present. Windows, fluorescents, etc. If that's not true then press for a change. The gels will eat a large chunk of the output and costing real money. The gels will burn out fairly quickly too.

You can fine tune your brightness with 'neutral density' gels. Basically shades of gray. For longer term use metal screens are far more durable. Both can be stacked in a light for precision control. All pretty common in photography.
Probably depends on how often the lights are on. One church I worked at had work lights so the stage lights were only on for events and never all of them, but like 3 hours per week. Another church I worked at had no such thing as work lights so most of stage lights were on about 6-8 hours every day.
 

danTt

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The other reason I've seen a goal for a specific higher temperature is if there is a projector or video screens in play, especially if doing live broadcasts as well--While some projectors let you turn the color temp down to 3200, it looks really weird live.
 

FMEng

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Consider the fact that TV studios used halogen lights for decades and most of the time without color correction gel because they didn't want to lose light. It sure wasn't a 5600 world, yet the results were excellent.

5600 is not a reasonable goal. Modern video cameras are very good at adapting to a wide range of light source color temperatures. 2800-3200 from halogen will look the same on a white balanced camera as 5600 on a white balanced camera. The goal should be consistency. That is, all light sources illuminating human flesh be near the the same color temp.

The way to achieve consistency while using S4 halogen is simply to dim them to the same level, whether that be full or 80%. The cameras will have some limitations on how much range in color temp they can adapt to, so dimming too much will cause color issues, but you can certainly dim a bit to improve lamp life.

Of course, where you want color washes, then the color temperature of the source becomes irrelevant. There you can use gels, LEDs, dimming, whatever.
 

RonHebbard

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Consider the fact that TV studios used halogen lights for decades and most of the time without color correction gel because they didn't want to lose light. It sure wasn't a 5600 world, yet the results were excellent.

5600 is not a reasonable goal. Modern video cameras are very good at adapting to a wide range of light source color temperatures. 2800-3200 from halogen will look the same on a white balanced camera as 5600 on a white balanced camera. The goal should be consistency. That is, all light sources illuminating human flesh be near the the same color temp.

The way to achieve consistency while using S4 halogen is simply to dim them to the same level, whether that be full or 80%. The cameras will have some limitations on how much range in color temp they can adapt to, so dimming too much will cause color issues, but you can certainly dim a bit to improve lamp life.

Of course, where you want color washes, then the color temperature of the source becomes irrelevant. There you can use gels, LEDs, dimming, whatever.
Matching your Carbon and / or Xenon Supers to the remainder of your lighting while still keeping them visible for their operators to accurately and consistently follow your featured performers is another thing to be dealt with.
Spike marks and spot sites will help with the accuracy of the your 'pick' points from your 120' throw but following a fast moving solo dancer's an entirely different matter ( and you don't want to look like a newb' on national / international TV Don't ask me how I know ).
Toodleoo!
Ron Hebbard
 
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Hey, just know that as a first-time poster here on CB, all of your responses are extremely helpful and encouraging! Thank you!

A little bit more background:
  1. We are broadcasting primarily IMAG for in-room projectors. We also use LED walls for creative set designs, and on top of that, we use all LED intelligent PARs and moving head lights for backlighting and aerial breakups. It's a pretty fully-featured worship setup! This thus inspires the goal for 5600K, as this way, the LED wall content behind the musicians and pastors will appear similar to it's actual appearance on camera.
  2. With all things ministry-related, when people are donating their money and trusting us to use it, I always try to be as frugal as possible, while still delivering the best results. This way, I would like to stay away from burning through ND gel, just to control brightness
Here is my plan, so far. Tear it apart; your advice is awesome!
  • Use a mix of 375W, 575W and 750W lamps, depending on the fixture's distance from stage. 750W for longer throws, 375W for the shortest
  • Set all fixtures to the same dimmer intensity, ~70%, so that there is at minimum about 30 footcandles in every focus area
  • Use a little ND gel to adjust fixtures to output the same illuminance
  • Use some level, yet the same level, of CTB in all fixtures, to get somewhere cool, close to the 5600K of the LED wall
 

MNicolai

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Given the amount of other technology already going on I would explore either upgrading to Colorsource Spots or doing the S4WRD II Daylight LED retrofits for your existing fixtures. Some time in the next few years it's likely you'll have to pull that thread so might as well put a plan in place for pulling it sooner rather than later. Eliminates your gel and lamp costs and get you to the color temp you want. May or may not be the cash on hand to go that route now but I'd least look into the costs because it will give you better results than attempting it with tungsten.
 

derekleffew

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  • Use a mix of 375W, 575W and 750W lamps, depending on the fixture's distance from stage. 750W for longer throws, 375W for the shortest
I'd be careful with this approach. You probably already use wide (50°) fixtures for short throws and narrow (19°) for long throws (or similar), right? Unless you're willing to do the math (but it's not all that hard--another Excel sheet attached) I'd stick with 575w.

  • Set all fixtures to the same dimmer intensity, ~70%, so that there is at minimum about 30 footcandles in every focus area
I'd say 70% and 30 fc are both too low. I'd try to start at 90% and 50fc.

Also note that a little variation in color temperature may not be the worst that can happen. It can be used to enhance angle (direction), thus providing definition and revelation of form.
 

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You probably already use wide (50°) fixtures for short throws and narrow (19°) for long throws (or similar), right?
In trying to achieve similar angles for front light, the throw distance per fixture varies. I am using a variety of 19, 26, and 36-degree lenses for downstage, midstage, and upstage areas.

Our stage is small, ~25' across. I don't have access to our plot with the exact dimension right now. For the midstage section, I divide the stage from left to right into (5) areas in order to gain more control, as opposed to (3) areas like the upstage and downstage sections. This way, I use tighter, 19-degree lenses for these. I plan to use lower-wattage lamps here to compensate for the higher illuminance.

I'd like to use tighter lenses and lower-wattage lamps rather than just using the framing shutters. Am I thinking along the right lines?
 

FMEng

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With a video wall in the background, the need for 5600 makes sense. If stage lights aren't about the same color temp, the wall may look blue on camera. The correction would be gelling halogen lights and tolerating the light loss from the gel, or using LED lights.

I know next to nothing about video walls, so let me ask a question. Can the color temp of the wall be adjusted warmer? It seems like it would be possible.
 

MRW Lights

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Broadcasting Live Performance is a very large part of my job for a national broadcast network... You are not restricted to a static color temperature from the stage lighting. Period. You may be limited by the technology available to you which typically comes to the table from two sides "video"/"Theater". Video will almost always want it brighter because it's easier and Theater will almost always want it darker because it provides wider range and more emotion. If you have the ability to do a manual white balance of your cameras and the capability to shade/paint them using a vectorscope and calibrated reference monitor there is absolutely no need to achieve a static color temperature or intensity. 5600k at 100% intensity sounds like a nice forced AUTO WB level for a camera.... do you have access to the video side of the information, switcher and cameras? Chances are, and here's the sales pitch to your "bosses", balancing the photometrics correctly for both the eye and the camera should result in a better image for everyone. Don't force the camera/eye to do the work of the other. Adjust the image correctly and it will look great for everyone.
 
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With a video wall in the background, the need for 5600 makes sense. If stage lights aren't about the same color temp, the wall may look blue on camera. The correction would be gelling halogen lights and tolerating the light loss from the gel, or using LED lights.

I know next to nothing about video walls, so let me ask a question. Can the color temp of the wall be adjusted warmer? It seems like it would be possible.
I like how you're thinking. The entire wall can be color balanced at the control processors, so it can be set to a warmer white balance. At this point though, I think all the content would be odd to the naked eye for the audience, since the content is designed for 5600K.