word usage - Why "think bright" is used with adjective instead of adverb (think brightly)?

I find "think bright" is much more common usage, but why? In my opinion, "Think" is a verb, so it is reasonable to use adverb to describe it.

Examples:

THINK BRIGHT!

^{(Source: MISIS)}

Answer

In think bright, bright is used as an adverb. This is similar to think different. Such adverbs--whether standard or not--are called flat adverbs, because they lack the -ly ending associated with most adverbs. For example, in I had to think hard about this sentence, hard is a flat adverb.