Questions about gels and temperature options

[Denis Haineault]

Hi,

I'm getting close to snapping and ordering some lights, but would like a few clarifications about gels and color temperature options:

- I understand that CTB gels will absorb a good amount of light, but I'm unclear if CTO gels are just as bad. My guess is that loss of light does occur, but not as much ??

- Assuming CTO gels aren't as bad as CTB for light loss, does it make sense to have only daylight balanced bulbs, and use CTO gels whenever you need 3200'ish temperatures? I mean that in terms of ease and flexibility gear-wise.

- Assuming you have total control of the light sources, and you want to (say) make your picture a bit warmer, is there an advantage to using gel on lights instead of modifying the temperature setting in camera? Is it just a matter of personal preference?

- I know that in reality, color temperatures vary greatly when it comes to actual daylight, gel manufacturers, bulbs of all kinds, etc. but assuming "perfect" conditions, and assuming all the options are available to you, is there an order for using gels vs using different bulbs, vs adjusting temperature in camera? Does one yield better result over another, or does it end up being the same whatever you choose?

thanks,
Denis

 

[Paskaler]

- I understand that CTB gels will absorb a good amount of light, but I'm unclear if CTO gels are just as bad. My guess is that loss of light does occur, but not as much ??

Hi! I have used both of them and CTB absorb a little more light than the CTO's, but it could be a psychologic perception, since cold colors seem darker than warm colors.

- Assuming CTO gels aren't as bad as CTB for light loss, does it make sense to have only daylight balanced bulbs, and use CTO gels whenever you need 3200'ish temperatures? I mean that in terms of ease and flexibility gear-wise.

It depends on what you want to do. For example, I've used CTB's for night time lighting. Sadly, daylight balanced bulbs are sometimes not bright enough, and halogen worklights (which are bright enough) are yellow, so you're gonna need CTB's.

- Assuming you have total control of the light sources, and you want to (say) make your picture a bit warmer, is there an advantage to using gel on lights instead of modifying the temperature setting in camera? Is it just a matter of personal preference?

I think it's better to use gel on lights. Modifying the temperature setting in camera could even look good on the small LCD screen, but when captured it could look irreal. Of course, everything depends on the effect you're trying to achieve. You could play with the white balance, too, using pale orange and blue cards.

- I know that in reality, color temperatures vary greatly when it comes to actual daylight, gel manufacturers, bulbs of all kinds, etc. but assuming "perfect" conditions, and assuming all the options are available to you, is there an order for using gels vs using different bulbs, vs adjusting temperature in camera? Does one yield better result over another, or does it end up being the same whatever you choose?

Man, the Force is not strong enough on me

 

[Andrew Brinkhaus]

I'll add some more detail here-

In general, daylight units (HMI particularly) are going to output more light at the same wattage than a tungsten source would. Meaning, even though the wattage is very similar, if you were to use a 1.2k HMI next to a 1k tungsten light, the HMI would be putting out near the equivalent of a 5k tungsten. They also convert heat better, daylight units convert a much higher percentage into usable light as opposed to heat emission.

When it comes to gel, particularly CTB and CTO, my recommendation would be if you can afford daylight units, go for it! You will always save light output by using CTO on a daylight unit as opposed to CTB on a tungsten light. O has roughly 50% transmission, where as B has only 35%. This will also depend strongly on the situations you shoot in, the size of the lights needed, as well as the quality of light, which is affected by the lights "lens" sometimes a fresnel, variable removable lenses, or no lenses at all (like a work light).

Lighting practice and theory is incredibly expansive, and the concepts of gelling lights and controlling the tone, color and exposure on set primarily by lighting has been the staple of a cinematographers job for decades. Sure there are times that enhancing the color balance in camera is necessary, but for the most part, I would always recommend doing your color work physically on set as much as possible.

Best of luck!

 

[Denis Haineault]

Thanks for the replies

...I would always recommend doing your color work physically on set as much as possible.

Best of luck!

I was already leaning towards that idea, but wanted to check what others think. In my self-study journey, the idea of capturing in-camera as much as possible (not just for lights) is a concept I adopted early. It just seems to make more sense to me.

Assuming the loss of light isn't an issue, are there times where using a different temperature bulb is preferable over a gel, even though the resulting temperature is rated the same?

 

[James Dierx]

It's dark out and I'm in a room. I have two omni lights and I want it to look like the light is coming from the moon. Would I set the white balance to 3200K and put CTB gel's on the lights?

 

[KKeller]

It's dark out and I'm in a room. I have two omni lights and I want it to look like the light is coming from the moon. Would I set the white balance to 3200K and put CTB gel's on the lights?

I would trick the white balance by putting an orange gel (1/4 or 1/2) in front of the lens and doing a white balance as normal. That way you don't lose any light from gelling your omnis.

 

[Denis Haineault]

It's dark out and I'm in a room. I have two omni lights and I want it to look like the light is coming from the moon. Would I set the white balance to 3200K and put CTB gel's on the lights?

If your bulbs are 3200k then yes, you can white balance your camera for that value, and then use CTB on your lights. Keep in mind that CTB will reduce your light source intensity by quite a bit (about 2/3), so make sure your lights are strong enough.

Alternately, KKeller's suggestion is another way.

You'll want to experiment to see which one looks best for your situation and equipment.