Lightning And Darkness

Riddle: There are four words. Two of them have four letters, and the other two have five letters. The four-letter words have two vowels and two consonants. The five-letter words have two vowels and three consonants. If you read one of the four-letter words backward, you will get the other four-letter word. If you put a consonant in the beginning of a four-letter word you'll get one of the five-letter words. If you put the same consonant to the end of the other four-letter word you will get the other five-letter word, which is also read backward as the first five-letter word. There is a correlation between the one of the four and one of the five-letter words. The same goes for the other two words. One pair has to do with something bad and the other pair has to do with life. What are the words?