What is the difference between 我像太阳 and 我像陽光燦爛著?
我像陽光燦爛著 means "I'm shinning like sunshine."

我像太阳 means "I'm like the Sun."

"I am like the brilliant sunshine." would be 我像燦爛的陽光

陽光燦爛著(yángguāng cànlànzhe) means "The Sun is shining."

著 is used for Present Progressive Tense or Present Participle. To put it simply, -ing.

The "brilliant" in the "I am like the brilliant sunshine." is a Adjective, so it should use 的(de)