Lighting greenscreen with green light- does it help?

Barry Gribble · September 30th, 2005, 09:27 PM

I did some work in a studio the other week where they had it set up to just throw green lights at a white wall and use that as a green screen. We weren't doing any of that, but I did ask the DP. He said that he personally was against they approach, but that the studio used it pretty often.

Wayne - are you sure that you would lose 1/4 of your green output? Certainly you lose a significant portion of the overall light, but I think that it will mostly be the blues and reds which would not make the green wall any brighter anyway. Do you lose green output with a green gel? Hmmmm, not sure.

Sean McHenry · October 4th, 2005, 07:36 AM

You shouldn't loose any green using a green gel. Look at IR photography. You can't get a deeper red filter than that. It effectivly blocks all visible light totally, but the IR wavelengths pass through and are illuminated quite nicely. The same is true for IR light emmiting panels. You can't see the light from the IR led in your remote controls (your camera quite often can - interestingly) and they are filtered heavily too yet they get enough of the right light to work fine.

When you gel a light source, you are adding a material in the light path that reflects, or absorbs the colors you don't want passing through. Blue gels let a certain wavelength through as do any color gel. Saturation of the gel color is a key to how well it blocks all the colors you don't want.

In those swatch books, and I haven't seen one for a while, they used to have a chart for each color explaining what portion of the spectrum gets passed with each gel. If it isn't getting passed, it's being absorbed so, white light with a green gel will absorb all those excess colors and allow your green to pass through.

The only reason I can see NOT to use a green filter is the splash and spill off the green gelled lights. You don't want that green light hitting anything it's not supposed to. If it's controlled right, I don't see anything particularly right or wrong with it.

I will finish by saying that green paint, or any color will not be perfect. If you use white light, a small amount of the other colors will still get reflected as that green paint, no matter how expensive a version you use, will still reflect other colors in minute amounts. You could minimize that by using predominantly green lighting.

I was thinking more about this just last night.

Sean McHenry

Harikrishnan Ponnurangam · October 14th, 2005, 02:47 PM

Based on my practical experience. I usually keep the green screen far away from the subject and lit with kino flo. As Walter expalined, use te corresponding backlight for background you would be keying in.

All does matter is the seeing it on the production monitor. If you can afford just do a sample testing using a NLE(FCP) right away, do it. Which i did at home. You don't have to get stressed about this and i wont use a white short for any of our artist period.

September 30th, 2005, 09:27 PM	#16
Barry Gribble Major Player Join Date: Aug 2003 Location: Los Angeles, CA Posts: 817	I did some work in a studio the other week where they had it set up to just throw green lights at a white wall and use that as a green screen. We weren't doing any of that, but I did ask the DP. He said that he personally was against they approach, but that the studio used it pretty often. Wayne - are you sure that you would lose 1/4 of your green output? Certainly you lose a significant portion of the overall light, but I think that it will mostly be the blues and reds which would not make the green wall any brighter anyway. Do you lose green output with a green gel? Hmmmm, not sure. __________________ Barry Gribble Integral Arts, IMDB

October 4th, 2005, 07:36 AM	#17
Sean McHenry Trustee Join Date: Mar 2004 Location: Hilliard, Ohio Posts: 1,193	You shouldn't loose any green using a green gel. Look at IR photography. You can't get a deeper red filter than that. It effectivly blocks all visible light totally, but the IR wavelengths pass through and are illuminated quite nicely. The same is true for IR light emmiting panels. You can't see the light from the IR led in your remote controls (your camera quite often can - interestingly) and they are filtered heavily too yet they get enough of the right light to work fine. When you gel a light source, you are adding a material in the light path that reflects, or absorbs the colors you don't want passing through. Blue gels let a certain wavelength through as do any color gel. Saturation of the gel color is a key to how well it blocks all the colors you don't want. In those swatch books, and I haven't seen one for a while, they used to have a chart for each color explaining what portion of the spectrum gets passed with each gel. If it isn't getting passed, it's being absorbed so, white light with a green gel will absorb all those excess colors and allow your green to pass through. The only reason I can see NOT to use a green filter is the splash and spill off the green gelled lights. You don't want that green light hitting anything it's not supposed to. If it's controlled right, I don't see anything particularly right or wrong with it. I will finish by saying that green paint, or any color will not be perfect. If you use white light, a small amount of the other colors will still get reflected as that green paint, no matter how expensive a version you use, will still reflect other colors in minute amounts. You could minimize that by using predominantly green lighting. I was thinking more about this just last night. Sean McHenry __________________ ‘I don’t know what I’m doing, and I’m shooting on D.V.’ - my hero - David Lynch http://www.DeepBlueEdit.com

October 14th, 2005, 02:47 PM	#18
Harikrishnan Ponnurangam Regular Crew Join Date: Mar 2005 Location: St.Louis, USA Posts: 145	green screen Based on my practical experience. I usually keep the green screen far away from the subject and lit with kino flo. As Walter expalined, use te corresponding backlight for background you would be keying in. All does matter is the seeing it on the production monitor. If you can afford just do a sample testing using a NLE(FCP) right away, do it. Which i did at home. You don't have to get stressed about this and i wont use a white short for any of our artist period.