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Color Temperature of Different HMI Lights


Fiza Chughtai
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10 hours ago, Fiza Chughtai said:

Why not white balance 1 or 2 stop over to save the extra step of adding half CTO?

I probably can't explain this well but please bear with me as I try Fiza. You are asking good questions but don't quite have the concept clear in your mind.

Think of our various lighting sources (HMI, Kinos, LED, tungsten, video screens) as a color palate you can paint with by utilizing the inherent difference in color temperatures emitted by the lighting sources themselves. However you must set a baseline reference that everything else is scaled off of.  Usually let's say it is a 3200K white balance on your camera. When you throw up your white card to set the white balance what color temp unit do you want to use to illuminate it? Well something that is close to 3200K. Maybe a Mole midget or inky or a 650 open face. A softlite with a 3200K quartz globe will usually have a color temp closer to 2900-3000K as (even if you use the official Mole white reflector paint) the unit's color temp warms up as the heat ages and yellows the reflector paint.

OK you've told your camera's little brain to render 3200K illumination as white. Every other lighting source that you as DP incorporate in the scene will render relative to your base 3200K white balance. The two 16K HMI's with 1/2 CTO up on Condors two blocks away will be your 1/2 Blue "moonlight" ,  The 3200K Ianiro Blondes with 1/2 CTO's hung up on telephone poles will be your orange warmish "Sodium Vapor" sources,  the uncorrected crappy cheap "daylight" florescent overheads in the sleazy motel office that's your principal location today, will have a ghoulish green cast.  The 650W Mole Tweenies nailed on to quarter apples in the flower beds around the office have an assortment of "party gels" adding to the atmosphere of the cheap motel. The full spectrum LED 12V strip lights inside your actor's car are dialed down to about a 3000k color temp to give a slight warm skin tone to the actor.

Do you see how your creativity and understanding of color temperature has allowed you to paint a scene with color without even picking up a brush?

 

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On 2/11/2021 at 6:10 PM, Fiza Chughtai said:

Thank you!...usually these are 3200K ?

They were (are?) available either way by which PAR 36 globe you lamp them with. The original FAY had a dichroic (sp?) coating that made them nominally 5000K but this quickly faded due to the heat. The Molefay's were used when you either couldn't afford Brute arcs or didn't have a space to use them or ventilate them such as an interior. When you lamped the Molefays with tungsten/halogen globes I think you had a choice of flood, medium, and spot depending on what throw and output you needed from the unit. Once HMI's started to enter the market you almost never saw a 9-lite lamped with daylight FAY's. Too expense and time consuming.

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7 hours ago, Doyle Smith said:

However you must set a baseline reference that everything else is scaled off of.

Do you see how your creativity and understanding of color temperature has allowed you to paint a scene with color without even picking up a brush?

 

Ya I understand how variables effect the impact of different lights' outputs. Thanks

On which factors to decide the baseline value (WB)?..for single source it may be easier to decide. But mostly I guess you are always using more than one light source, so whether day or night what are the factors to evaluate the decision of what to set as WB? and are there any common tried tested go to preferred values for shooting day and night scenes?

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Commonly, it's the colour temperature of the ambient light is a deciding factor.

Alternately, if you wish to create a colour effect, eg a moonlight effect or a sunset effect. 

There are also colour temperatures in between tungsten and daylight, which can be found on various fluorescent lights,

It's worth experimenting, because the most interesting lighting for a scene may not be a straight  tungsten or daylight white balance.  

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HMI lamps have very little real consistency between them. Ive seen them vary from as high as 6300k brand new out of the box to 4800k at the end of their life with varying levels of green/magenta.
 

Generally speaking you tend to be able to get away with all but the extreme ends of the scale. 

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  • 2 weeks later...
On 2/27/2021 at 9:40 PM, Matthew Parnell said:

HMI lamps have very little real consistency between them. Ive seen them vary from as high as 6300k brand new out of the box to 4800k at the end of their life with varying levels of green/magenta.
 

Generally speaking you tend to be able to get away with all but the extreme ends of the scale. 

Matt is right on with this. If you're using an HMI outdoors for fill with natural sunlight you likely won't perceive any color temp difference. If you use an HMI fill on an overcast day it is likely much warmer than the ambient skylight. Sometimes this works to your advantage to give you an attractive skin tone. Sometimes it looks too attractive if you're going for a depressing, ominous scene. In that instance, you might add a little plus blue to the fixtures. 

A situation where you need to match color temp on multiple fixtures would be say, if you lined up three 18K's outside large windows for a "Sun" source. You wouldn't want a vast color temp disparity between them. This is why good electrical departments baseline their fixtures before a show so they don't have to deal with this in the heat of battle.

Edited by Doyle Smith
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