LCD AND PLASMA TECHNOLOGIES

LCD TV

LCD (Liquid Crystal Display) televisions are primarily composed of a liquid crystal solution divided into individual pixels, which is sandwiched between two glass plates. A backlight is used to beam the light through the first plate, and an electrical current is passed through the crystals. The amount of charge applied to each crystal causes it to allow a certain degree of light to pass through. The resulting crystal formation is what forms the displayed image. As LCD panels produce no light of their own, they require an external lighting mechanism like a cathode fluorescent lamp.

Pros:

• Longer screen life
• No screen burn from stationary images
• Better glare response
• Lesser power consumption
• High contrast images, including fine text and graphics
• Brightest of all the display technologies
• The thinnest displays available and not very bulky

Cons:

• Slowest refresh rate of all the displays
• Brightness and colour response decrease as the viewing angle increases
• Possible uneven light distribution from the backlight

Plasma TV

Like LCDs, Plasma screens are composed of two glass panels. The difference between the two technologies lies in the substance between these two panels. Instead of filtering light, the panels house thousands of gas chambers, each behind red, blue, and green phosphors. An electrical current is used to turn the gas into plasma, which generates an ultraviolet light that causes the phosphors to glow, creating the desired image.

Phosphors are substances that give off light when they are exposed to other light. When an ultraviolet photon hits a phosphor atom in the cell, one of the phosphor's electrons jumps to a higher energy level and the atom gets heated up. When the electron falls back to its normal level, it releases energy in the form of a visible light photon. Every pixel is made up of three separate subpixel cells, each with different coloured phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colours blend together to create the overall colour of the pixel.

By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each subpixel colour to create hundreds of different combinations of red, green and blue.

Pros:

• Good colour quality
• High contrast images, including fine text and graphics
• Wide viewing angle
• Fast screen refresh rate making it suited for fast moving pictures
• Largest direct-view display technology available

Cons:

• Suffers from screen burn that is the result of lost phosphor luminosity in certain areas due to prolonged usage.
• Suffers from image retention (similar to screen burn) when some pixels are run at high brightness for a prolonged period.  But this is only due to charge build-up and there is a self-correction process after power down.