On a .500 light anything under a .500 is a red light and .501 would be the best light you can cut.

On a .000 light the lower the better.

.053 is a good R/T

 

When the tracks went to the new LED lighting systems the numbers dropped. Perfect light used to be .400 or .500 and now its .000. LEDs illuminate faster or something like that is why they changed it...I got the rulebook somewhere to find out for sure