DLP and LCD are based on "backlighting" (not the proper term but what the hay). They both use a bulb to either reflect off of mirrors (DLP) or to project through a blocking filter (LCD). Plasma and CRT depend on the "excitement" of either phospors or inert gasses to GENERATE light vs. MANIPULATE light. The problem with plasma and CRT is that if only a portion of the screen is "excited" in a regular manner the gasses or phospors will wear out quicker than in the others areas and cause burn-in since they will, when a "full screen" image is displayed, give off less light. This is also true (but they handle it better because of their inherent design) of direct view CRTS (have you ever seen an old CRT on an ATM machine that has the menu burned in?)