These are not regular glasses for the short-sighted. These glasses cheer you up.

Their surface contains fine parallel grooves or rulings that are equally spaced. It is so called diffraction grating. Particular colours are deviated in different ways.

These glasses should be worn by people who do not laugh enough. If they watched a colourful world they would cheer more.

Observing the world with these glasses one sees fascinating images - many light sources, full of rainbow colours. Colourful images are placed everywhere - on the horizontal line, on the vertical one and also in diagonal directions. They become slightly less intense moving away from the central image (which is white, and not colourful!). If a laser beam passes through these glasses, the central point is surrounded by many lateral points, forming a kind of cross.

The "glasses" made of transparent plastics, posses a number of tiny lines, posed at constant distances, both in the vertical and in the horizontal directions. Glasses like these can be considered as two, perpendicular sets of diffraction gratings, similar to that on a CD. When a light beam impinges such glasses, it undergoes diffraction, i.e. forms maxima and minima of intensity at well defined angles. Each line of the grid becomes a source of the light, and the light intensity sums-up or subtract, depending on the angle of observation. A phenomenon somewhat similar to that observed with soap bubbles.

The diffraction grating produces maxima of intensity for a given light wavelength only for the observation angles defined by the following equation:

a sin α = kλ ,

where a is the grating constant, i.e. the distance between the lines, k is an integer numbers defining the image order (i.e. defining how far a given image is away from the central one) andλ - is the wavelength. The intensity of the image diminishes with the rising order k.

In these glasses two diffraction gratings produce diffraction images in two directions. Note also that this photo does not show all "rainbow" colours. In the diffraction picture some colours are missing like the yellow one - these colours are really missing in the spectrum of the "economic" lamp.