Microsharp film targets LCD backlights

03 Jul 2006

UK firm Microsharp unveils a non-periodic film which it hopes will eliminate interference effects generated in LCD backlights.

Unwanted interference effects generated by the thin-films used in an LCD's backlight could be a thing of the past thanks to a UK display technology firm called Microsharp. The firm has just applied to patent a film structure that it says reduces the scope for moiré interference effects from so-called polymer prismatic films.

Nearly all LCDs contain one or two polymer prismatic films in the backlight that illuminates the display. One problem with these films is that the repeating pattern of prisms can lead to moiré interference effects. This can occur between the pattern in the film itself and the reflected image of the pattern from other surfaces within the display.

David Bottomley, the commercial manager of Microsharp, believes the firm has come up with a solution: a film that consists of peaks spaced in a non-periodic fashion. In comparison, the films commonly used in today's displays have a periodic pattern of peaks and valleys at 90 degree internal angles to each other and a peak-to-peak spacing of 50 microns.

"This is a conceptual breakthrough within the field of polymer prismatic films," Bottomley told optics.org. "The film is made in a reel-to-reel process, with widths up to one meter. It is then cut up into pieces for individual displays. Greater computer control of the manufacturing process is helpful in making the film."

According to Bottomley, one way to think about the differences between the common and Microsharp films is in frequency space. "The periodic film has a period corresponding to the 50 micron peak-to-peak spacing, as well as its harmonics at 100 microns, 150 microns and so on," he said. "The non-periodic film has many more possible peak-to-peak spacings, hence it is markedly different in frequency space. This structure reduces the scope for moiré interference effects."

Although reluctant to give away too many details, Bottomley explains that in one example, the Microsharp film consists of peaks that are spaced non-periodically using the digits of π to create the random spacings. "The nth peak spacing is derived from the value of the nth digit of π," he said.

With the global LCD market booming, Microsharp's patent application could put it in the right place at the right time. Bottomley adds that the firm plans to put the film into mass manufacture before the end of 2006.