This is a very popular illusion and one of those that you might have seen several times in the social media sites. This is the reason why he could not help ourselves but post it here in our site. Probably you need no explanation on what to do but it is our duty to tell you that. Just stare at the image for half a minute or a full minute and then shift your eyes to any white surface. It can be your ceiling, you wall, your floor and if you have nothing, it can be a plain white sheet of paper. You will see that the bulb is glowing.