Everyone has an internal "light" inside of them. No, we don't actually glow...sorry to get your hopes up... but we do radiate a certain vibe. Being around someone whose crabby, can put you in a bad mood...the same thing can happen with GOOD moods, too! Happiness and love are GREAT lights to shine... but the best thing to show others is God's light!
"In the same way, let your light shine before others, that they may see your good deeds and glorify your Father in heaven." Matthew 5:16
If you glorify God, and you act in a loving and godly way, that light will SHINE out, and people will be able to see God through YOU! Like this song by Jamie Grace,
If you strive to show Jesus in everything you do, you will truly SHINE. People will appreciate your love and kindness even if they don't know Jesus-- BONUS: you might even allow someone to get to know God, by YOUR actions!!
This isn't always going to be easy... we all have rough days, but remember to never let anything or anyone stop you from SHINING.