POLARIZATION OF NATURAL LIGHT REDUCES EYES

Natural light, such as the sun, for example, is an electromagnetic wave that can create glare when directly stared or exposed to the reflection of that light. To reduce or obstruct eye glare can be used as aids such as glasses. Various types, shapes and brands of eyewear on the market have their respective functions. Anti-UV black-lensed glasses normally block the wavelength of UV light, namely UV-A (315 - 400 nm), UV-B (280 - 315 nm), and UV-C (200 - 280 nm) with colored filters or lenses polarization. Polarizing lenses convert natural light that has a large intensity into polarized light that has a smaller intensity. These polarizing glasses generally reduce reflective glare from horizontal surfaces such as reflected light from water, roads or snow. Then how is theoretically the polarization of light in glasses to reduce eye glare?

Polarized light can be obtained by using an optical instrument known as a polarizer (polarizing filter). Glasses with polarized filter lenses (polarized) is an example of a polarizer that is able to absorb or block certain wavelengths of natural light. Polarizers behave like filters, absorbing certain parts of the vibrational direction of light waves, so that the intensity and direction of vibrations of certain waves are still present and continued by the polarizer.

As is known that, light as an electromagnetic wave consists of components of the magnetic field (B) and the electric field (E). Non-polarized light waves lead in all directions and are perpendicular to each other in the direction of vibrational propagation of the waves and displayed in the same degree. Illustration of non-polarized light is presented in Figure (a) and polarized light in Figure (b).

 Figure a. Non-polarized light                                                                  Figure b. Polarized light

Each series of electromagnetic wave radiation is emitted by an atom in a radiation beam. In all light polarization methods, both reflectance, absorption, refraction and scattering methods, each component of the vibrational plane of the light wave that comes to the polarizer, will be made as a whole or partially forming an angle (q) with the direction of the polarization plane.

Theoretically, if a natural light with intensity (I₀) comes about the polarization filter, then according to Malus law, which was first released in 1809 by Etienne Malus, a military engineer and captain was put on Napoleon, the intensity of the light passed on by the polarizing filter (I ) is: I = I₀ cos²q

In this case the polarization filter will only transmit the electric field vector component (E) in the polarization direction. The component of this electric field is proportional to cos q. It can be seen from the formula above that, the intensity of the natural light transmitted by the polarization filter is always smaller than the intensity of the incoming light which depends on the angle q. This means that the intensity received by the eye using polarizing lens glasses is reduced.

                                        Figure c. Linear polarization and analyzer

In Figure (c) shows the second ideal linear polarizer (analyzer) which is identical to the first (polarizer) and the vertical transmission axis. The intensity measured by the detector when the maximum radiation occurs at an angle q = 0 is I (q) = I₀ cos²q. In this case I₀ is the intensity of the light coming on the analyzer. If 1000 W / m² of natural light comes in the first linear polarizer as shown in Figure (c), then assuming that the polarizer is ideal, the polarizer will pass 500 W / m² of linear light to the analyzer. As an alternative, suppose that linear light of 1000 W / m² comes parallel to the first polarized transmission axis, then in this case I₀ = 1000 W / m². The most common type of linear polarizer used today is the polaroid filter.

From the description above it is clear that, the arrangement of the polarizer will greatly influence the intensity of the light transmitted by the polarizer (polaroid) to the glasses and which will be received by the visual organs of the eye. Also be aware of light in the range from 450 nm to 650 nm, because ordinary polaroid is not very good at polarizing IR light.