Television replacement has taken on a speed comparable to computer upgrades. The rapid pace of advancement has created a profusion of options for HDTVs and a lot of confusing marketing pitches. One that can be clarified easily is the basic display technology comparing LCD to LED HDTVs.
1Differences Between LCD and LED TVs: In spite of the marketing effort put into making them sound different, LCD and LED HDTVs use almost the same technology for their displays -- a liquid crystal display with three color elements in red, green and blue that combine to make a single pixel. The vast majority of HDTVs use 1,080 pixels, or 1080p, as their primary resolution; only the least expensive models on the market still come in 720p. Where they differ is in the backlight. An LCD display uses a compact fluorescent lighting element as the backlight, while the LED display uses light emitting diodes.
2Purchase Price and Cost of Ownership: Television manufacturers have moved to LED production lines. LED backlights are cheaper for manufacturers to produce, and they produce a better quality picture. There are still plenty of LCD televisions available but very few new ones are being made. Expect those LCD TVs to eventually be put on deep discounts and get sold off, though it hasn't happened just yet. As a final cost-related item, LED displays are more energy efficient than the compact fluorescent backlights, and they're less likely to wear out over the service life of the TV.
3Image Quality and Screen Size: LED HDTVs have better picture contrast than LCD screens. Compact fluorescent backlights provide light at all times, even when the picture on the screen is supposed to be mostly dark. LED displays have one LED behind each picture element that may have as many as 256 brightness settings that can be tuned individually, by pixel. Some of the more advanced models even have four or nine very small LEDs to adjust the brightness at a sub-pixel scale. While LCD screens used to have "ghosting" problems, where watching fast moving images would get blurry as the screen's response time wasn't fast enough at the pixel level, since 2010, this problem has mostly vanished.
4TV Size: While there are still some very large LCD TVs on the market, LED TVs dominate this market segment; the first LED TVs were large-screen models for home theater enthusiasts who wanted the better contrast ratios, and LED backlighting has moved to smaller and smaller televisions over the last few years. If you're presented with a choice between an LCD and LED TV in a large size, both models in your price range, take the LED TV. LED backlights are still the only ones used on high-end televisions. The prototype "4K" and "8K" resolution screens (so called because they have four times or eight times the resolution of a 1080p HDTV) use LED backlighting.