Screen Blending Mode Produces Strange Behavior

[Santeri5E3B]

I just installed Illustrator to work on some personal projects, but quickly ran into a weird problem that I can't figure out. The screen blending mode (as well as lighten) don't actually lighten objects behind them, but instead, result in unexpected effects. As an example, I simply made a shape with a white-to-black gradient and set the blending mode to screen and another shape on the same layer behind the gradient shape. The result is shown in the attached image.

Things work totally as expected if I use the multiply blending mode.

Thanks for any suggestions!

[Monika Gause]

Are you working in CMYK or RGB documents?

[Doug A Roberts · Accepted solution]

Is your document CMYK?

Because (in CMYK) a black-to-white gradient only has one ink in it (from 0% K to 100%K), the equation for screen only works on the amount of K in the underlying shape. If there's no K there, you'll get white (zero times X equals zero).

[Santeri5E3B]

Yes, switching to RGB fixed it. Thank you for your explanation!