For example, H-Cl has a dipole. The electrons spend more of their time near the Cl atom (the red end in the diagram below). A dipole-dipole interaction is the attraction between two polar molecules. When they approach each other, the negative end one molecule attracts the positive end of the other.
Eyes sensitive to light can also be caused by viruses or inflammation, such as those found in sinus infections. If you have a cough, aching jaw, blocked nose, headaches and lethargy then it's best to visit your GP for a diagnosis of a possible sinus infection and simple antibiotic treatment.
To test visual sensitivity a more careful experiment must be performed. The retina at the back of the human eye has two types of receptors, known as cones and rods. The cones are responsible for colour vision, but are much less sensitive to low light than the rods. In bright light the cones are active and the iris is stopped down. This is called photopic vision. When we enter a dark room, the eyes first adapt by opening up the iris to allow more light in.