What is a scanning backlight?

Shopping for an HDTV can feel overwhelming. Not only must you learn a whole new set of terms, but you also have to decide between different HDTV technologies. Should you opt for a projection television? Do you want a flat-panel display? Is a plasma TV the best choice, or would an LCD TV suit you better?

As you explore the options, you'll uncover the unique pros and cons of each technology. For instance, plasma TVs tend to use more energy and take longer to heat up than LCD models. However, plasma displays are often superior in displaying fast-moving images with higher contrast than LCD screens. What makes plasma TVs stand out?

One reason for this is that LCD televisions rely on a backlight. Essentially, these TVs use a light source behind the screen that illuminates it. The way an LCD works involves sending electrical signals to millions of small liquid crystals, which change shape in response to the current, allowing light to pass through. The action displayed on an LCD screen is the result of the synchronized movement of these tiny crystals.

However, this technology does have its drawbacks. In most LCD models, the backlight remains on whenever the TV is powered, even if the screen is displaying dark scenes. In a completely dark room, you'd still notice the faint outline of the LCD screen, even when it’s supposed to be showing pure black. This means that for many LCD TVs, the contrast between the brightest whites and the deepest blacks isn't as striking as it is on plasma TVs, which don’t rely on a backlight.

The constant backlight can also lead to motion blur on LCD screens. It interferes with the sharpness of fast-moving objects, and in some cases, you might even notice trails left behind by particularly swift movements on the display.

To combat motion blur, LCD TV manufacturers employ various techniques. One such solution is the scanning backlight technology.

A Moving Backlight

Unlike traditional backlights, a scanning backlight doesn't remain on continuously. Instead, it activates precisely when and where needed to create images. By rapidly switching on and off – hundreds of times per second – this light minimizes blur and enhances contrast simultaneously.

Because the light can adapt to the images being displayed, it turns off when portions of the screen transition to black. This improves the depth and distinctness of black areas compared to what you'd see on a standard LCD TV. When paired with an HDTV that has a high refresh rate, you should also notice reduced blur.

Scanning backlights must be capable of turning on and off in the blink of an eye. While a conventional backlight might take a few seconds to warm up, a scanning backlight doesn’t have that luxury. If it can't activate or deactivate almost instantaneously, the viewer would still experience blurring or fading on the screen.

Typically, a scanning backlight comprises multiple light sources targeted at specific regions of the television's rear. Generally, these light sources are pricier than standard backlights, meaning an LCD HDTV with scanning backlight technology may be more expensive than similar models with traditional backlighting.

Not all LCD HDTVs are equipped with a scanning backlight. Even in models that feature one, you might need to adjust your settings to enable it. Meanwhile, refresh rates are on the rise: Standard-definition TVs refresh 60 times per second, while modern HDTVs can refresh as many as 480 times per second. While manufacturers claim that higher refresh rates result in smoother action displays, viewers may struggle to differentiate between a high-end model and an ultra-high-end version. Before making a significant investment, you may want to evaluate whether you can actually perceive any advantage.