I've found that it's not possible to breed a light dragon without first having a light dragon, and I find this sad...if you look at the eggs they tend to have the theme of the colors that make up the egg are connected to being able to breed the dragons...the colors that make up this dragon's egg are primarilly blue and yellow, so I figured that you could breed those to get the light dragon, but alas 'tis not the case. all of the breeding combonations to get a light involve having a light before hand, And though I understand that it is a dragon you can purchase for a fair amount of coins, being one who likes to try different combonations to get the dragons and having multiple ways to get all but the basic starting ones (IE fire, forest, water, and air) that i'm currently aware of aside from this one it is a oddly frustrating block in my opinion.