Hello; An LED tv is an LCD. The LCD (liquid crystal display) has to be lit from behind by a source of light, A basic LCD is backlit with fluorescent bulbs while a LED-LCD tv is backlit by LED lights. The LED is reported to have the advantage of using less electricity to operate the lights, the LED lights should last much longer. The fluorescent bulbs will slowly grow dimmer over time.
The other aspects of an LCD tv are the same for the LEd lit and the fluorescent lit. There are two key rates for LCD displays. One is the time it takes for liquid crystals to go from being the darkest and allowing the least amount of light thru to being the lightest and allowing the most amount if light thru and then back to being the darkest. This time should be 4ms or quicker. The other rate is the rate that the picture can refresh. The first LCD's were at 60 hrtz. At 60 hrtz there were picture quality issues during afst action scenes in movies or ball games. The makers have added some electronic to make the rate around 120 hrtz which had made the issues better.
If you are use to the old CRT (Cathode ray tube) tv's you may well see some artifacts and pixelation with an LCD, I did.
I eventually settled on a plasma. The plasma has a native picture much closer to the old CRT, 600 hrtz I believe. They can be adjusted so that they are not so brite and thus use less power. The makers have also worked on reducing power consumption. I can have three preset levels of brightness and color saturation. For ordinary watching I have one set fairly low. For some special tv shows I have one set a bit briter. For movies i have it set for a fairly dynamic picture. A plasma is more suited to a dark viewung room and lights and such will reflect onto the screen. I had to add a darker layer under my drapes to cancel the light and allow better viewing during daylight. Plasma screens are glass and can be cleaned without special cleaners. It is my understanding that LCD screens are a plastic that can be damaged with the wrong sort of cleaner or cloth. I am satisfied with the plasma so far and only have the question of longevity to be answered.