There is a very good free online ebook from South River - they make different types of miso.
Little Book of Miso – Recipes by South Riverhttp://www.southrivermiso.com/pdf/misobook.pdf
In the ebook they write:
"Miso is just as versatile in summer cooking as it is for winter meals. Although we recommend particular types and quantities of miso in our recipes, feel free to substitute other varieties (see page 22). One teaspoon of a dark miso is roughly equivalent in salt content to 1½ to 2 teaspoons of a light variety. Above all, enjoy this wonderful healing food. "