Approach
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Real glidepath deviations that fully change the lights are under one degree, far too small to draw to scale. The aircraft's vertical position here is exaggerated so you can see it move; the numeric readout and the lights themselves are accurate.
Quick check
The lights are showing this pattern. What should you do?
Reading the lights
PAPI and VASI tell you where you are relative to the published glidepath, typically around 3° but check the chart for the actual angle. Neither gives lateral guidance or protects you from obstacles beyond the system's own design case, they don't replace the approach chart, and under IFR you still respect your minimums.
PAPI: four lights in a row
Four units beside the runway, each showing red or white. Two red and two white means on the glidepath. More white than red means you're high; more red than white means you're low. All four the same colour means you're well off, in that direction.
VASI: red over white, you're all right
Two bars, a near bar and a far bar. On the glidepath the far bar (which appears higher in your view) shows red while the near bar shows white, "red over white, you're all right". Both white means high, both red means low.
Why red and white
Each light unit is a single lamp split by a coloured lens: viewed from above the design angle it reads white, from below it reads red, with a narrow transition band in between. There is nothing to interpret about brightness or shape, only colour.
What they don't tell you
Nothing about your track left or right of the runway centreline, nothing about terrain or obstacles beyond the certified approach, and nothing once you're too close in (the useful range typically ends a few hundred metres from the threshold). Cross-check with the runway picture and your instruments, don't fly the lights alone.