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5: Optical Mineralogy
5.3: Polarization of Light
5.3.3: Polarized Light Vibrating at an Angle to a Polarizing Filter

5.3.3: Polarized Light Vibrating at an Angle to a Polarizing Filter

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5.21.jpg — 5.21 Polarized light encountering a polarizing filter

Suppose polarized light hits a polarizing filter at some angle such that the light is vibrating neither parallel, nor perpendicular, to the polarization direction of the filter. In this case, only the component of the light that is vibrating parallel to the filter will pass. The filter absorbs the rest.

Figure 5.21 shows this happening. An original light beam travels vertically from below and encounters a filter. The light is vibrating nearly perpendicularly to the vibration direction of the filter but a small amount – the component that is vibrating parallel to the filter – gets through. If we rotated the filter, the amount of light transmitted would range from 0 to 100% depending on the orientation of the filter with respect to the polarization direction of the light from below. If the light from below is polarized east-west and the filter is polarized north-south, no light will pass through it (Figure 5.19). If we slowly rotate the filter to an east-west orientation, it will gradually transmit more light, and eventually, all of the light.