This effect arises due to slight misalignments of the beam which are a result of magnetic irregularities. Extreme magnetic fields deflect the beams from their intended direction, thus the phosphor point cannot be fixed exactly. This results in brightness changes and consequently colour patches.

If no measuring equipment is available, the best way to evaluate colour purity is to use a whole white or red screen.

Click on this field to enter the next step/level, further test pattern. This test pattern is especially designated for engineers or service staff who can then dispose of the respective measuring instruments.