This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2009) (Learn how and when to remove this template message) CRT projector Main article: CRT projector Advantages: Achieves excellent black level and contrast ratio Achieves excellent color reproduction CRTs have generally very long lifetimes Greater viewing angles than those of LCDs Disadvantages: Heavy and large, especially depth-wise If one CRT fails the other two should be replaced for optimal color and brightness balance Susceptible to burn-in because CRT is phosphor-based Needs to be "converged" (primary colors positioned so they overlay without color fringes) annually (or after set relocation) May display colour halos or lose focus LCD projector Main article: LCD projector Advantages: Smaller than CRT projectors LCD chip can be easily repaired or replaced Is not susceptible to burn-in Disadvantages: The Screen-door effect: Individual pixels may be visible on the large screen, giving the appearance that the viewer is looking through a screen door. Possibility of defective pixels Poor black level: Some light passes through even when liquid crystals completely untwist, so the best black color that can be achieved is a very dark gray, resulting in worse contrast ratios and detail in the image. Some newer models use an adjustable iris to help offset this. Not as slim as DLP projection television Uses lamps for light, lamps may need to be replaced Fixed number of pixels, other resolutions need to be scaled to fit this Limited viewing angles DLP projector Main article: Digital Light Processing Advantages: Slimmest of all types of projection televisions Achieves excellent black level and contrast ratio DMD chip can be easily repaired or replaced Is not susceptible to burn-in Better viewing angles than those of CRT projectors Image brightness only decreases due to the age of the lamp defective pixels are rare Does not experience the screen-door effect Disadvantages: Uses lamps for light, lamps need to be replaced on average once every year and a half to two years. Current models with LED lamps reduce or eliminate this. Estimated lifetime of LED lamps is over 100,000 hours. Fixed number of pixels, other resolutions need to be scaled to fit this. This is a limitation only when compared with CRT displays. The Rainbow Effect: This is an unwanted visual artifact that is described as flashes of colored light seen when the viewer looks across the display from one side to the other. This artifact is unique to single-chip DLP projectors. The Rainbow Effect is significant only in DLP displays that use a single white lamp with a "color wheel" that is synchronized with the display of red, green and blue components. LED illumination systems that use discrete red, green and blue LEDs in concert with the display of red, green and blue components at high frequency reduce, or altogether eliminate, the Rainbow effect.