for 3D playback but use halved vertical resolution (540p) instead. Disadvantages Flicker can be noticed except at very high refresh rates, as each eye is effectively receiving only half of the monitor's actual refresh rate. However, modern LC glasses generally work in higher refresh rates and eliminate this problem for most people. Until recently, the method only worked with CRT monitors; some modern flat-panel monitors now support high-enough refresh rates to work with some LC shutter systems. Many projectors, especially DLP-based ones, support 3D out of the box. LC shutter glasses are shutting out light half of the time; moreover, they are slightly dark even when letting light through, because they are polarized. This gives an effect similar to watching TV with sunglasses on, which causes a darker picture to be perceived by the viewer. However, this effect can produce a higher perceived display contrast when paired with LCDs because of the reduction in backlight bleed. Since the glasses also darken the background, contrast is enhanced when using a brighter image. When used with LCDs, extreme localized differences between the image to be displayed in one eye and the other may lead to crosstalk, due to LCD panels' pixels sometimes being unable to fully switch, for example from black to white, in the time that separates the left eye's image from the right one. Recent advancements in the panel's response time, however, has led to displays that rival or even surpass passive 3D systems. Frame rate has to be double that of a non-3D, anaglyph, or polarized 3D systems to get an equivalent result. All equipment in the chain has to be able to process frames at double rate; in essence this doubles the hardware requirements. Despite a progressive fall in prices, due to the intrinsic use of electronics, they remain more expensive than anaglyph and polarized 3D glasses. Because of their integrated electronics and batteries, early shutter glasses were heavy and expensive. However, design improvements have resulted in newer models that are cheaper, lightweight, rechargeable and able to be worn over prescription lenses. From brand to brand, shutter glasses use different synchronization methods and protocols. Therefore, even glasses that use the same kind of synchronization system (e.g. infrared) will probably be incompatible across different makers. However, efforts are being made to create a universal 3D shutter glass. Alternated viewing of left and right views leads to an effect of