Cindy,
The method of the 'bright light' is usually called 'candling'
This is basically how it works. Use a bright light to 'shine through' the hatchling's vent. For males, you can properly see the hemipenes of the male. This is a bright red organ (with all those blood vessles..)
I have only heard of doing this way with hatchlings only. i have never heard of anyone doing it on adults.
Poping would be more accurate for hatchlings. This is what I do....and never have tried 'bright light'
Probing is the most affective method of sexing a snake.
But both poping and probing shouldn't be done unless someone experience shows you how. If you do it on your own, you COULD injure the snake and affect its breeding organs.
Bringing your snake to an expereinced breeder or vet would be the best way to sex your snake plus learn how to pop or probe a snake.