A light, that contains electromagnetic waves with all oscillations directions of vectors E and H (if they are mutually perpendicular and perpendicular to the direction of the light travels), is called unpolarized or natural light. The sources of such light are the sun or electric bulbs par example. On the contrary the light vibrating in one preferential direction is called plane-polarized light. Some materials, such as a sheet of Polaroid film, cause unpolarized light to become polarized after passing through the film. The devices that serve to transform unpolarized or partially polarized light to plane-polarized light are called polarizers. With help of this activity you can study a model of the simplest polarizer and can observe the effect of a Polaroid materials on the intensity of light passing through it. You see on the left a bulb. The bulbs light is unpolarized; yellow arrows represent its possible oscillation directions. Two films have selected directions of light transmission (they are shown by dash-dot line). The second film can be rotated with help of floating band control. The direction of the light traveling serves as the axis of rotation. Therefore the directions of light transmission for different films can be placed about variable angle one relatively another and the intensity of light passed through both films can be changed. The box at the bottom of the simulation indicates the intensity of light passing through both films compared to the intensity of light Io emitted by the bulb.