Been a long long time since I watched that movie, but iirc V'ger's cloud was something like 80 au (astronimical units) i.e. the average distance from the Sun to Earth or about 150 million kilometers (93 million miles). Multiply by 80 is roughly 12 billion kilometers (7,5 billion miles)
That's big. If you were to center V'ger over the sun, it would extend all the way to the orbit of Pluto. But a lightyear is bigger. Several orders of magnitude bigger. It's a mighty 9,46 trillion kilometers (5,88 trillion miles). And that's really big. Space is really big. How big?