on those pixels that require it, and only to the amount of brightness they require. In spite of the light-generating process being less efficient than CCFLs or LEDs, the overall power efficiency of a SED is about ten times better than an LCD of the same size. SEDs are also much less complex in overall terms – they lack the active matrix layer, backlighting section, color filters, and the driver electronics that adjust for various disadvantages in the LCD shuttering process. Despite having two glass layers instead of one in a typical LCD, this reduction in overall complexity makes SEDs similar in weight and size to LCDs. Canon's 55" prototype SED offered bright images of 450 cd/m2, 50,000:1 contrast ratios, and a response time of less than 1 ms. Canon has stated that production versions would improve the response time to 0.2 ms and 100,000:1 contrast ratios. SEDs can be viewed from extremely wide angles without any effect on the quality of the image. In comparison, a modern LCD television like the Sony KDL-52W4100 claims to offer 30,000:1 contrast ratios, but this uses the "dynamic contrast" measurement, and the "on-screen contrast ratio" is a more realistic 3,000:1. Contrast ratios of LCD televisions are widely inflated in this manner. The same set claims to offer viewing angles of 178 degrees, but the useful viewing angles are much narrower, and beyond that, both color gamut and contrast ratio changes. Sony does not quote their response times, but 4 ms is common for larger sets, although this is also a dynamic measurement that only works for certain transitions. SEDs are very closely related to the field emission display (FED), differing only in the details of the emitter. FEDs use small spots containing hundreds of carbon nanotubes whose sharp tips give off electrons when placed in a strong electrical field. FEDs suffer from erosion of the emitters and require an extremely high vacuum to operate. For this reason, industry observers generally state that the SED is a more practical design. FEDs have one advantage the SED does not offer; since each sub-pixel has hundreds of emitters, "dead" emitters can be corrected by applying slightly more power to the working ones. In theory, this could increase yields because the chance of a pixel being completely dead is very low, and the chance that a screen has many dead pixels is greatly reduced. Sony has demonstrated