Projected image from a video projector in a home cinema. A video projector takes a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other inconsistencies through manual settings. Video projectors are widely used for conference room presentations, classroom training, and home theatre applications. A video projector may also be built into a cabinet with a rear-projection screen (rear-projection TV, or RPTV) to form a single unified display device, now popular for ?home theater? applications. Common display resolutions for a portable projector include SVGA (800?600 pixels), XGA (1024?768 pixels), 720p (1280?720 pixels), and 1080p (1920?1080 pixels). The cost of a device is not only determined by its resolution, but also by its light output, acoustic noise output, contrast, and other characteristics. While most modern projectors provide sufficient light for a small screen at night or under controlled lighting such as in a basement with no windows[1], a projector with a higher light output (measured in lumens, abbreviated ?lm?) is required for a larger screen or a room with a higher amount of ambient light. A rating of 1000 to 1500 ANSI lumens or lower is suitable for smaller screens with controlled lighting or low ambient light.[1][2] Between 1500 and 3000 lm is suitable for medium-sized screens with some ambient light or dimmed light. Over 3000 lm is appropriate for very large screens in a large room with no lighting control (for example, a conference room). Projected image size is important; because the total amount of light does not change, as size increases, brightness decreases. Image sizes are typically measured in linear terms, diagonally, obscuring the fact that larger images require much more light (proportional to the image area, not just the length of a side). Increasing the diagonal measure of the image by 25 % reduces the image brightness by 35 per cent; an increase of 41 per cent reduces brightness by half.