That sentence can not be used. Even i can't understand what it exactly mean. If you write what you want to say in English, I'll check and fix it to Korean. so... If you want to say "why is the light so strong" you should say 왜(why) 이렇게(so strong) 조명이(the light is) 밝아요(bright)? [왜 이렇게 조명이 밝아요?] and it perfectly make sense. 이렇게 can be used various way and it is a little confusing (and my English is more confusing... sorry)

Yes, you can say '밝다' for any source of light. It sometimes also mean 'brilliant' in a way. For example, '그는 컴퓨터에 밝다' means "He's knowledgeable in computer". But I could hardly parse your own example.