OK, so I'm gearing up (at the SO's request) to tackle Ezra Klein's Kung Pao Tofu recipe and his posts talk about how in developing his sauce, using *both* dark and light soy sauces is key.

I'm long past the point of purchasing Kinkomans or the grocery store stuff. I get a nice (giant) bottle at H-Mart these days. But I have no idea if it's the dark or the light.

Anyone have definitive answers on lights/darks? And a stab-in-the-dark at which I already own?

Many thanks!