I've never seen heavy jungle appear in a game, at least I haven't seen it. Light jungle is in the Kokoda games and Saipan and its expansions. Heavy woods, or its variations of dense woods or forest, appeared in Lions of Finland, Arctic Front and Arctic Front Dx, and that by GSR.
So, I wouldn't say there were light/heavy woods as part of my nomenclature, it would be light/regular in the absence of a special rule. That said, the rule which would apply would be based on the percentage of the more severe terrain. The standard (per
rule 8.24) is 25%. My method is determining a half of a half by laying ruler or LOS thread across the corners of a hex, with the questionable terrain all on one of the ruler/thread. In the light/regular woods question, if the regular woods art is more than half of that half, it's a regular woods hex. Also, try to resolve questionable hexes before starting the game.
