I have a Nikon D5300 and always shoot on Auto White Balance because it can be easily fixed in Lightroom or other RAW Processing applications. However, I wanted to experiment a bit with shooting Video on the Camera, so I need a proper white Balance.
As all stores are closed now and I'm a big fan of DIY, I was starting to wander if you could use a phone screen with 18% grey or some other neutral color (white should work as well) as a grey card (the D5300 doesn't allow for fully manual WB). Could this work or is it problematic that the phone is emitting the light by itself and not reflecting the natural light? (I have a Samsung Galaxy J7 if that should matter)
I'm also aware of other methods like using a sheet of paper or printing 18% grey on it (however, my printer is not very accurate), but wondered if the phone wouldn't be more accurate.