VASI :-

VASI is a simple glide slope indicator used in VFR. Basically there are three indications. RED RED, RED WHITE, WHITE WHITE - meaning Below glide slope, On glide slope, Above Glide Slope respectively.

PAPI :-

PAPI is another VFR glide slope indicator but has, as its name states, more precision. It contains 4 lights and the indications use the WHITE and RED indicators - similar to the VASI. However, PAPI provides more slope angle information. Such as:

WHITE WHITE WHITE WHITE = you are high - more than 3.5 degrees.

WHITE WHITE WHITE RED = you are high - just at 3.5 degrees

WHITE WHITE RED RED = you are on the glide slope

WHITE RED RED RED = you are low - just at 2.7 degrees low.

RED RED RED RED = you are more than 2.3 degress low (RED means DEAD).