Some edge-lit TVs also come with local dimming support. But the number of backlight zones is typically far lower than in full-array TVs, and the individual LEDs are responsible for lighting up entire columns of the screen. So edge-lit local dimming is much less precise, and the benefit in terms of contrast ratio is minimal.

Because edge-lit is the more "premium" technology, edge-lit TVs do tend to be somewhat more expensive than a direct-lit TV of the same size. As a result, most of the gigantic, inexpensive (relatively), 4K displays you'll see for sale are direct-lit, and almost all of the least expensive, smaller TVs you'll see are too. Ultimately, that is a good thing. Not every situation calls for the slight advantage edge-lit displays provide, and in those cases, why not save a buck?

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As direct-lit TVs require fewer LEDs and no backlight control, they are cheaper to produce and thus typically limited to the entry-level and mid-range segments of a TV manufacturer's portfolio.

Broadly speaking, edge-lit TVs will provide better visual quality than direct-lit TVs, and you should probably pick an edge-lit display if you're concerned about visual fidelity. Most of the mid-range television sets you see for sale online and in stores are edge-lit, but you should always confirm that before making a purchase.

Mini-LED TVs offer more local dimming zones, which means improved contrast and deeper blacks. They're not hugely expensive, either. Here's what you need to know.

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Edge LED backlighting first appeared in TVs in 2008, allowing for a thinner profile than LCD TVs with other backlighting solutions. But as the LEDs are placed on the rim of the screen, edge-lit TVs require a diffuser to light up the entire display adequately. This adds to their cost, making them slightly more expensive than direct-lit TVs. But given that backlighting is just one part of an LCD TV's cost, you will find both cheap and costly edge-lit TVs on the market.

Most farms have at least one high intensity discharge lamp (HID) lighting up the yard at night. A mercury vapor (MV) light is one type of HID lamp. However, the mercury vapor lamp is the least efficient of HID type lamps and poses a greater environmental risk than other types such as high pressure sodium (HPS) lamps and metal halide (MH) lamps. A HPS lamp emits about 95 lumens/watt while MH lamps emit about 60 lumens/watt and a MV lamp emits only 32 lumens/watt, the lowest of the HID type lamps. The metal halide lamp provides the best color rendering light and should be considered for replacing MV lamps in areas where color recognition is important such as a dairy freestall barn. Many lamp manufacturers have HPS or MH retrofit lamps that can be used to directly replace a mercury vapor lamp without replacing the fixture, but these are expensive, costing as much as a new fixture with the lamp. A 100-watt HPS lamp can provide 2.5 times more light than a 100-watt MV lamp while a 100-watt MH lamp produces 155% more lumens.

Modern LCD TVs rely on LED backlighting to produce the visuals you see on the screen. But their picture quality and price can differ based on their backlighting system. So, what are these backlighting systems, and how are they different?

Metal halide lamps are available in a standard version and a pulse-start version. The pulse-start is newer technology which results in up to 50% longer lamp life, about 8% more lumens per watt, faster warm up and restarts and up to 33% less lumen depreciation over the lamp life. They should be considered for any new fixtures. However, the lamps for pulse-start metal halide (PSMH) cannot be used in standard metal halide fixtures and standard metal halide lamps cannot be used in PSMH fixtures. Therefore, if adding new fixtures to an existing installation, it is recommended that all fixtures be upgraded to pulse-start ballasts and lamps to eliminate inventory issues.

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The LED backlight zones in full array and edge-lit TVs are significant as they enable the manufacturers to implement a feature called local dimming. It allows TVs to control the backlight on a scene-by-scene basis. So the TV can turn off LED backlighting in parts of the screen where it's supposed to be darker while keeping other parts lit. As a result, LCD TVs with local dimming can produce deep, uniform blacks and have a better contrast ratio than the LCD TVs that don't have this feature.

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As we mentioned previously, there are always going to be variations in quality between models and manufacturers that complicate comparisons of this sort. A well designed direct-lit TV will probably look much better than a poorly designed edge-lit display, and there is no definitive way to know in advance if that will be the case.

How does a HID lamp work? A HID lamp consists of an arc tube (or sometimes called a discharge tube) filled with a gas. In the case of a metal halide lamp, it contains a starting gas (usually argon), mercury and metal halide salts. When the lamp is operating, a high voltage is applied to the gas mixture in the tube causing it to vaporize and emit light and UV energy. The outer jacket or bulb provides a stable thermal environment for the arc tube. If the HID lamp is turned off, it has to cool before it will re-light or re-strike which can take 5 to 20 minutes.

Unfortunately, LCD TVs with full-array local dimming can also suffer from various screen artifacts, such as blooming and black crush, depending on the number of backlight zones and the overall local dimming implementation.

If you are shopping for a new TV and curious about its backlighting system, you can consult the TV's specifications. Manufacturers generally mention whether an LCD TV is direct lit, edge lit, or full array. In the case of full-array TVs, the number of local dimming or backlight control zones is also listed in the TV's specifications. This number is usually different for different sizes of a particular TV and can impact the amount of contrast ratio gain you can expect.

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Low bay HID fixtures are typically used in freestall barns (see photo at right). They should be a wide distribution type which usually means they will have a diffuser or cover over the lamp to diffuse some of the light horizontally. It is recommended that the fixture be rated for a damp environment with a gasketed diffuser.

Direct lighting is the newest of the three types backlighting in LCD TVs. The first commercial direct-lit LCD TVs emerged around 2012 and are essentially an off-shoot of the full-array TVs.

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When is it time to change a HID lamp? Because HID lights do not have a filament to burn out like an incandescent bulb, they don’t just stop working but instead just fade away as they age. If the lamp lumen output is severely degraded the lamp should be changed. The second indication that lamp replacement is needed is frequent shutting down and re-striking while power is applied to fixture. It is best to change the lamps at approximately the rated life which is usually 20,000 hours or more.

Full-array TVs have the best backlight implementation among LCD TVs. Not only do these TVs have a large number of LEDs, but the LEDs are also divided into multiple zones for dynamic backlight control. So, depending on the number of backlight zones and local dimming implementation, full-array TVs can have modest to excellent improvement over the native contrast ratio of the LCD panel. Increasing LED density increases the number of dimming zones, and successive generations of "mini-LED" TVs have marked improvements.

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As a result, full-array TVs typically deliver deep blacks and bright highlights and are generally excellent for displaying HDR content.

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But, the lower number of LEDs also means they have to be placed farther away from the screen to offer sufficient light coverage across the panel. As a result, direct-lit TVs are usually thicker than TVs with other backlighting systems.

LCD TVs can be grouped into three categories based on the type of LED backlighting system: Direct-lit, edge-lit, and full-array. As the name suggests, direct-lit TVs feature a panel of LEDs placed directly behind the display stack. Full-array TVs have a similar LED placement, but the number of LEDs is significantly more, and these LEDs are divided into different zones. But unlike both direct-lit and full-array TVs, edge-lit TVs have LEDs on the perimeter, and depending on the TV, these LEDs may or may not be grouped into multiple zones.

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Additionally, the lack of backlight control limits the contrast ratio of direct-lit LCD TVs to the native contrast ratio of the panel. So if a direct-lit TV uses a VA-type LCD panel, it will have a reasonable contrast ratio, but TVs with IPS-type panels have a poor contrast ratio.

All-in-all, the backlight system of an LCD TV can impact its picture performance. And if you are shopping for a new TV, full-array TVs generally have the best picture quality. But if you are restricted by your budget, direct and edge-lit TVs can also deliver good visual performance. But make sure to read expert reviews to get a better idea about the overall quality of a particular television. If you can, go see a television in person at a store somewhere — after all, it is going to be your television, and no amount of technical analysis or review reading can beat a direct answer to the most important question: Does it look good to me?

OLED TVs are self-emissive and don't need a backlight, unlike LCD TVs. Instead, each pixel of an OLED panel can generate its own light and be switched off to display the perfect black color. So, OLED TVs essentially offer pixel-level local dimming. As a result, they have a near-infinite contrast ratio and are generally considered to have the best picture quality. But they are also typically more expensive than LCD TVs and can suffer from burn-in.