Ship - Color Temperature Question


Active Member
Hi Ship - since your the lamp & color temperature king, I have a question for you.

On my stage we run both conventional fixtures & High End Systems intellys.

I have Colortran 5/50 Ellipsoidals using the HX754 lamp. 750W, 115V. The lamp is rated at 3200K, but I usually only run the lamp at about 74%. Will the reduced wattage cause the color temperature to go down? Any pictures I take all the other colors look normal (intellys, CYC, etc.) but anyone under ellipsoidals looks orange. I do have Bastard Amber gels in them. I have a picture if you want to see one....


Well-Known Member
1) The bastard amber gel reduces color temp significantly, and I mean a LOT !. Probably a couple of hundred degrees, not to mention a corresponding decrease in intensity due to the gel.

2) Your movers run at CT's up around 5600K or so

3) If you project a 3200K light on a white wall alongside a ML, with no filters, the ML will look slightly blue.

4) Your eye is attracted to the brightest object on stage, thus you see the ML's before the C-Tran with the BA gel.

5) Reducing the voltage on an icandescent lamp reduces color temp.

5) Cameras, especially digital cameras, see light differently then the eye, but there is no way the Colortran at 75%, with a bastard amber gel, is EVER going to look as white as an ML.

So what's the question ?.



Senior Team Emeritus
Premium Member
HX-754 / GLD are nice lamps, how do you like them? Dependable, shock resistant, refined filament sufficient to project a pattern? The Philips #6981P is about the same lamp but 1,500 Lumens more in output and 100 hours more life. I would recommend switching to it.

For every 1% change in voltage less than the lamp's stamped operating voltage, color temperature will be reduced by 0.4%.

This figure is only useful when you meter the voltage at the fixture when the dimmer is set to full. Than do the math in accounting for the difference between that voltalge asl no doubt different than that of what's stamped on the lamp. Than deduct that from your 74% to get the true color temperature the lamp is operating at.

I expect that in a rough guess it would be about 78% which gives you roughly 3071 K in color temperature. Very roughly as it's been many years since I have had math class.

Given 3.5% less output per percentage in output, why are you normally running this fixture at 74%? Wouldn't something like a HPR 575/115 lamp work better in the fixture for output when left at full? Or some mixture of lamps at partial where punch is needed and most at full? This no longer having to fight "Amber Shift" than would bring the lamp up to it's rated color temperature and above it by way of operation over stamped voltage of the lamp no doubt when at full - normally over 115v. Your actual color temperature might be something around 3.3K when at full which is why most 115v lamps look hotter/blue in color temperature than the older styles of Leko using 120v lamps. Granted your fixture lamp life would be also reduced by 12% per volt percentage drop.

So let's see, moving light arc source lamps. Hmm, my follow spot is too bright, whell that's why it's called a follow spot is it not? Same story with using arc source intels with conventionals. Way different beams of light.

If you specify what fixture you are using, dependant upon what that arc source fixture is, there might be a 3,200K arc source lamp available for it. High End even at one point had a lamp on the market called the INdy 575. It was made by Amglo and was a filament lamp for use in a studio spot. I have something like two of them left and Light might have more available. Othewise the 250w versions have the new ST-250HR lamp from Philips available by now which is at 3,200K. This lamp should - not tested or looked into yet, but should work in most 250w moving light fixtures.

You can or should be able to thus in a 575w or 250w moving light fixture, bring it down to 3.2K in color temperature. Otherwise with all such lamps there is a range from 5.6K to 7.8K in color temperature available. Given say you lower the color temperature of your lamps some, and color correct the color temperature of your conventional fixtures, you should be able to get into the 5.0K range for both without a problem given gel used.

In the end, you have amber shift from dimming, two different color temperature fixtures in use and the oh' by the way amber gel in use. Before you do anything, start by using a lighter amber gel in the fixture. This should start to correct the problem by way of transmission level of the gel each step less dark you get.


Apollo Staff
Premium Member
Thanks for the detail explanation, Ship.
This happens somewhat often within the theater and corporate community, and your handy formula will certainly assist us all-

Thanks again,


Active Member
Ship - thanks for the thurough explanation. Great!

I don't really have alot of experience with lamps, so when you ask me how I like the HX754 lamps, I guess I like them because I havn't really had any problems with them.

I routinetly use GOBOs on my CYC using those fixtures with that lamp and yes, the gobos come out pretty well.

Why don't I switch to the HPR-575 lamp, I don't know. I hate the idea of having lots of lamps to mess with. But I guess adding one more couldn't hurt.

I'm actually now looking into lighting the preaching platform with 2kW Colortran fresnels. I don't know if you can see it on the picture or not but the ellipsoidals are hung at a nasty angle, and there are some serious shadow & hot spot problems. Plus, I've been wanting to get my hands on some more fresnels in my stock for a while, so it seemed like a good excuse for the paper pushers.

I'm not looking to change my color temp on my intellegents. I love the "bright" light that they produce. When we do concerts, plays, or shows, and we use haze they are stunningly bright & white - with tons of punch. I love my HES fixtures!

Maybe I'll order a couple of those lamps and try them in those ellipsoidals, and see if there is any noticble difference.


Active Member
I just realize I didn't post any pictures - sorry. But believe me they are hung at about 28 degrees, ick!


Senior Team Emeritus
Premium Member
Lots of lamps in the inventory is the bane of problems in anyone's inventory. Now where even for me was that HPR free sample located as opposed to the HX-400x lamps I normally use? Standardization is a good thing, my hope would be that you as a in general thing go to in all fixtures the HPR lamp for high output but less wattage given big budget shows, or GLA lamps for the more normal shows in long life - both 575w. Your saying you need 1Kw lamps or high output 750w lamps says to me that this extra punch is wasted in having no as it were head room in having more power... - this amp goes up to 11. The lamp as a goal you should be using is a 575w/115v lamp for the general purpose fixtures. Front of hous lights due to distance might move up to 750w/115v or even EHG series 120v lamps in counter acting the "Law of Squares", but for the most part, a lessening of the general intensity on stage in wattage/light might be advisable so you have head room to get effect lighting where needed. Believe me, you lessen all intensity in general on stage and you get used to less light. There is no reason to max out the fixtures other than by way of tradition. What seems bright now will by way of your eyes seem just as bright some time later with lesser wattage lamps. Than at that point for effects you do have head room or as a term room to up the output for special purposes. It's all just a question of training your head into what in a dark room seems bright, and adjusting the ausience to becoming used to less intensity thus being bright. Hard to do and a sort of shame someone maxed your fixtures out but I assure you that a 575w. lamp should be for all intensive purposes bright enough.

In a controlled atmosphere where a single source candle on stage might at times seem bright, this indicates that you have once the audience is used to the amount of light you provide what level of lighting is required. How did even them 1960's shows get by with incandescent lights. This all granted that you have them moving lights and kind of like the follow spot like seperation of individual beam to them. That's part of using fixtures and above them lamps available within the fixtures as just brushes in your general pallet of light beam. This in addition to the gels of choice you have in painting the scene. Banancing the color temperature of the moving lights is an option, so is, keeping the difference in beam from that of other fixture. One big pallet of paint brushes to paint the scene with.

Hope you tried lessening the gel saturation before you tried anything else because it sounds like that might solve the problem initially before you buy a bunch of new brushes.

On further purist advice if of any use, Remember that the 45 degrees of "the method" is just a formula. Yuck!, is but a noted response to observations laid out in the McCandless formula. He is very clear in specifying that while for general effective natural lighting on the subject, you have to work with what you work with. Perhaps if at 28 degrees, some Fresnel fill on the exact same circuit from an opposing more harsh angle might make your 45 degree goal effective again when gelled and balanced the same. Say even something at 78 degrees in wash when balanced with something at 28 degrees provides enough light from a general direction to make up for that 45 degrees up and out angle. This including the horizontal angle when the fil is high side and intendant beam is at low lesser angle.

Just a theory or concept on my part however. Might choose some 500w fill lamps/fresnels or even Pars in MFL beam while high side to help balance that 28 degree front light.

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