White balance and lighting

1. SidneyMyers
   Member

   

   I shoot video mainly for fun (my kids sports/family events etc..) but I have done a few shoots for money.  I intend to start my own videography company in a few years and I am trying to develop a good base of knowlege now.

   I do not have much experience at all with lighting.  This has been an area of focus for me recently.  One of the questions that I keep asking myself is why do we have to worry about not intermixing different light set ups that use different color temperature bulbs? 

   If a person was to use two different types of bulbs that have different color temperatures can't the camera simply factor these out by doing a manual white balance?  I know that I must be missing something here.  To me it seems that by doing a manual white balance using a white piece of paper (or other white item) that we are "telling" the camera that "this is white" and the camera will then get the colors correct no matter what lights we are using.

   If anybody has time to reply and help me understand what I am missing that would be great.

   Thanks.

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2. robgrauert
   Member

   

   Hmm...I'll take a stab at this.

    Lets create a hypothetical situation. Let say you're lighting a person in a scene and you shine a florescent bulb and a tungsten bulb on the person. You may be able to put a piece of paper in front of the subject's face and white balance properly for his or her face, but then what about the areas being affected by spill from lights? You may have blotches of green(from the florescent) or orange(from the tungsten) beyond your subject since those areas may not have the same mixture of light. 

   Does that make sense?

   Also, I think cameras may sometimes have a hard time white balancing properly when there is a mixture of color temperatures.

   Robert J. Grauert, Jr
   www.robgrauert.com

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3. chrisColorado
   Member

   

   True. I've seen that the background behind the subject would look more green on the side of the florescent, and more orange on the side with the tungsten. Also, I'd think that you want to make it as easy for your camera as possible so you don't risk ending up with something strange.

   This makes more difference/matters more if there's a window involved since you might want the window in the shot, so you'd have to avoid white balancing to something other than daylight.

   I do see SidneyMyers point though. I didn't start studying lighting until after I'd been doing video for a year. Many of the lighting techniques I learned didn't seem to matter much at first.

   Basically, even if you white balance, I've learned that the camera will still show that the colors are a little different from each other and that doesn't send a good message to viewers/clients. The lighting, like the editing, should be invisible.

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4. SidneyMyers
   Member

   

   Great points guys, thanks for helping.

   Sid Myers

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5. BarefootMedia
   Member

   

   I can be a bit more specific about the difficulty you'd encounter by describing the physics of lighting.

   The strength of a light source decreases at the square of the distance from the source.  So when you white balance at one location, everything at that location will look okay.  But moving a foot one way or the other, the balance betwen the lights' colors changes at a geometric rate (rather than a linear rate.)  So all the objects on either side of the white balance point will not be recorded with proper colors.  So even the background will have a slow transition from being of in one direction, to correct in the middle (or where the white balance was set,) to tinted in the other direction.  Essentially, almost none of the image will have the correct hue.  And to correct it in post would require extreme skills & really high end color correction tols.

   If you want to see how dramatic the effect is, try lighting only one side of the set.  Put your camera on manual and set exposure at a middle point, then watch what happens as you move from one side to the other.  Using exposure, the differences are very obvious and identical to the color shifts you'd encounter.  And just as impossible to fix in post.

   Now there is one situation where it is possible to skake by using different color tempature lights.  If you light the front of the set with one color of light, then light the background (and even perhaps your hair light) with the other temperature of lighting.  When you white balance using the lighting falling on the talent, you will get accurate color for your talent, but the background will be recorded incorrectly.  But you have to be really careful about the light spilling onto the set itself.

   So that's that.  Good luck with your productions and have fun.

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6. D0n
   Member

   

   the most obvious problem, in practical terms is this:

   you set the white balance on your subject, and the shadows will have an obvious color cast. if you move your camera or your subject, the color will change.

   you can use that effect to positive ends creativly....

   for example....

   you place a ct (yellow/orange) gell in front of your camera lens and set a custom white balance to compensate. you then place that same ct gel on your main  light and light your subject. (or place the gel on the light and set color balance at the subject)your subject will be color corrected and everything else will be tinted (guess what color? hint: opposite color on a color wheel). now suppose you have one or two more lights the same as your main light (stronger ct gels), which you use to rimlight your subject (they'll wind up having a color cast because of your white balance setting).

   using the above technique will yeild the following:

   a normal colored subject, with yellowish (warm) rimlighting against a blueish (cool)background effectivly using color to seperate and pull forward your subject from it's cooler (pushed back) background.

   cool colors appear to recede and warm colors appear to come forward.

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7. SidneyMyers
   Member

   

   This is all great stuff, thanks to everyone who took the time to write in and help me.

   Thanks,

   Sidney Myers

   Posted 1 year ago # Login to Send PM

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