Confusion regularly comes among Chinese soy sauces and Japanese soy sauces. Roughly, there are three types of Japanese soy sauces:
Light soy sauce does not mean less sodium soy sauce at all. If a recipe calls for light soy sauce, try to determine if it's a Japanese or Chinese recipe. If the recipe is Chinese, light soy sauce means Chinese light soy sauce or regular soy sauce. If it is Japanese, it may mean usukuchi soy sauce.
Less sodium soy sauce is usually more expensive. It is because the process to produce low sodium soy sauce requires the same initial amount of salt and the same procedures as for regular soy sauce. The difference is an additional step at the production end to remove certain amount of sodium (40% usually)