What is a 18% grey card

Hi guys,
What is a grey card? What does it do? Is it used for "exposure levels" or "white balance"? What is the significance of 18%. Can you suggest relevant articles on this subject. I appreciate any help you can give, thanks.

White balance, although some use it for exposure too, but this only works if the subject is quite uniform in "brightness" (no highlites, no blacks).

18% is neutral - not white, not black.

I use a white "card" extensively for flower shots where the colour balance can be critical (although my "white card" is a fold-up cloth). One side is white, the other 18% grey.

LIGHT METERING = The basics of metering systems

https://photography-on-the.net/forum/showthre​ad.php?t=368397

https://photography-on-the.net/forum/showthre​ad.php?t=326164

https://photography-on-the.net/forum/showthre​ad.php?t=188006

Need an exposure crutch?

An 18% gray card is theoretically a representative of 'the average scene brightness', so it serves first to be a good metering substitute when the actual subject is 'not typical', such as a white polar bear or white bride in white wedding gown, or black cat or black groom dressed in a black tux. Second use, and what most digital users are familiar with, the gray card can also serve as a color neutral patch for White Brightness post processing or custom WB settings in camera.

Glenn NK wrote in post #4421913
White balance, although some use it for exposure too, but this only works if the subject is quite uniform in "brightness" (no highlites, no blacks).

18% is neutral - not white, not black.

If you're talking an 18% Kodak Gray Card--which is probably the most common one--it is used for exposure, and NOT white balance, as it is not spectrally neutral.

18% gray cards are primarily used for exposure. They are also white on the back. The latest versions of the cards are in fact color neutral and work quite well for white balance (custom white balance doesn't really care if the subject is white or not, but rather that it's color neutral).

Mark

For a technical discussion, see:
http://doug.kerr.home.​att.net/pumpkin/Scene_​Reflectance.pdf
and
http://doug.kerr.home.​att.net …/Exposure_meter​ing_18.pdf

Cheers

Peter Pawinski wrote in post #4422517
If you're talking an 18% Kodak Gray Card--which is probably the most common one--it is used for exposure, and NOT white balance, as it is not spectrally neutral.

Not Kodak; I was referring to my fold-up white balance disk (made by Color Balance Coach). I use the grey side but have tried the white side and get the same results. It fits in my shirt pocket.

Glenn NK wrote in post #4423478
Not Kodak; I was referring to my fold-up white balance disk (made by Color Balance Coach). I use the grey side but have tried the white side and get the same results. It fits in my shirt pocket.

Just wanted to make clear for others that not all gray cards are made the same.

Hey, thanks everyone for your time and help, I appreciate it greatly.