In conventional (twisted, nematic) TFT layers, the liquid crystals (LC) are twisted when there is no voltage impressed on them since a lower molecule aligns to the lower intermediate layer and an upper molecule aligns to the upper, offset by 90 degrees, intermediate layer, as shown in picture 1. The polarized light is twisted with the tilted LC molecules at an angle of 90 degrees and passes through the other upper polarizer, thus making the pixel illuminate (white).
The liquid crystal molecules align vertically when a voltage is applied. The light is not twisted and blocked by the upper polarizer resulting in a black screen.
Since the LC molecules near the intermediate layer still have an improper angle, they cause a diffuse refraction and diminish the contrast. At a moderately leveled input signal, the LC molecules are aligned at a certain improper angle (just not absolutely vertical). This causes a diffuse refraction and a decrease in contrast as well. The delay coating compensates this diffuse refraction and improves the contrast, hence widening the usable viewing angles.
A TN LCD monitor is operates at a relatively low voltage which required a smaller amount of power to be consumed. The production yield is better than those of other methods.