Attraction between the plates can be easily understood by focusing on the one-dimensional situation. Suppose that a moveable conductive plate is positioned at a short distance a from one of two widely separated plates (distance L apart). With a << L , the states within the slot of width a are highly constrained so that the energy E of any one mode is widely separated from that of the next. This is not the case in the large region L , where there is a large number (numbering about L / a ) of states with energy evenly spaced between E and the next mode in the narrow slot – in other words, all slightly larger than E . Now on shortening a by d a (< 0), the mode in the narrow slot shrinks in wavelength and therefore increases in energy proportional to −d a / a , whereas all the L / a states that lie in the large region lengthen and correspondingly decrease their energy by an amount proportional to d a / L (note the denominator). The two effects nearly cancel, but the net change is slightly negative, because the energy of all the L / a modes in the large region are slightly larger than the single mode in the slot. Thus the force is attractive: it tends to make a slightly smaller, the plates attracting each other across the thin slot.
In another study of blue light, researchers at the University of Toronto compared the melatonin levels of people exposed to bright indoor light who were wearing blue-light–blocking goggles to people exposed to regular dim light without wearing goggles. The fact that the levels of the hormone were about the same in the two groups strengthens the hypothesis that blue light is a potent suppressor of melatonin. It also suggests that shift workers and night owls could perhaps protect themselves if they wore eyewear that blocks blue light. Inexpensive sunglasses with orange-tinted lenses block blue light, but they also block other colors, so they're not suitable for use indoors at night. Glasses that block out only blue light can cost up to $80.