Does Light Have Mass or Is It Just Energy?

[David_Harkin]

I am a lower sixth student and i got into an argument with my physics teacher today when we were talking about the photovoltec effect and he said that light has no mass. I have a very small understanding of the subject compared to him but from what i do understand the uncertainty principle states that light can change the momenteum of something and so it must have mass to have momentium. Also i know that gravity can bend light and this also points out that it must have a mass. His response was that light is just energy until it hits something and then it changes its energy to mass.
I cannot grasp the concept of something existing of pure energy i was wondering if somebody could shed some light on this. Thanks

 

[cristo]

I recall a new addition to the FAQ regarding this a few days ago. Here's the link: https://www.physicsforums.com/showpost.php?p=1285138&postcount=6

 

[David_Harkin]

Thanks, i understand it now.