I haven't implemented the Phong model for many times but I'm confident it's correct. The only problem I've noticed is this. Seems like a quantization is taking place somewhere :
I'm not sure if it's visible enough. There are concentric circles on every flat surface of the cube I have. After testing on other models, I ensured that this shows up on flat surfaces. Moreover, when decreasing the light's power, the circles become bigger and get further from each other :
Is this a common issue?
Or should I start uploading my code?