There is no 상태동사 in Korean. I think you are confused with other languages such as English. There are only verbs and adjectives in Korean and nothing in-between.
The simplest way to distinguish 형용사 (adjective) from 동사 (verb) is to conjugate by placing '-ㄴ' or '-는' before '다' using the basic (root) form. If the conjugated form makes sense, it is a verb. If not, it is an adjective as follows:
- Changing the words to basic forms.
슬프네 -> 슬프다
예뻤지 -> 예쁘다
먹어라 -> 먹다
가신다 -> 가다
- Place '-ㄴ' (when the last word before 다 ends with a vowel) or '-는' (when it ends with a consonant) before '다'.
슬프다 -> 슬픈다 (X)
예쁘다 -> 예쁜다 (X)
먹다 -> 먹는다 (O)
가다 -> 간다 (O)
The first two are adjectives and the last two are verbs.
Let's see how your examples work.
강하다 -> 강한다 (X)
밝다 -> 밝는다 (X)
Neither of them works and it proves that they are adjectives.
When you see a translated version of those adjectives in Korean, it might sound like a verb, but there is no 상태동사 in Korean.