This comment was written after the second paragraph. Bill: This last paragraph sounds like a guess. As does a lot of this page. Jim Yu, I am sure, did a faithful translation, but this terminology is not generally used in English.
Dieter: Okay Bill, but it is used in the book. And I found it more intuitive than the whole komaster treatment. Sure a better job needs to be done describing these terms.
Bill: I am not objecting to the terminology, but I don't think that we can say much about its general usage in English. As for Chinese, I can't say anything at all. ;) I look forward to the examples, which should shed some light. :)
unkx80: This usage seems consistent in Chinese literature. As far as I understand, the "light" and "heavy" in "light ko" and "heavy ko" have the meanings as described in light and heavy respectively, i.e., one that can be easily sacrificed and one that cannot be easily sacrificed.
Bill: Very interesting, unkx80! :) Thanks. IIUC, a small ko is not necessarily light, then. Is that right?
unkx80: I guess, most small kos are light. My understanding is that the following applies to the Chinese as well:
If a ko is light for both players, it means that the ko is simply small, such as a one point endgame ko. In such a context the term is seldom used.
On the other hand, nobody would describe a game-deciding 1/3-point ko as "light".
Bill: Great work, Dieter! Thanks so much. :)
BTW, my guess is that a worry-free ko is the same thing as a flower viewing ko, which is the extreme form of a light ko.