Helping you make sense of the technological world...
ANSI lumens
ANSI lumens is a measurement of the overall brightness of a projector. Because the centre of a projected image is brighter than the corners, ANSI lumens is the most accurate representation of the image brightness. ANSI lumens are calculated by dividing a square meter image into 9 equal rectangles, measuring the lux (or brightness) reading at the centre of each rectangle, and averaging these nine points.
Contrast Ratio
If you're concerned about picture quality, don't just look at brightness. Contrast is just as important. In short, it's a measure of how well the projector can block out light from the lamp, ie. how black is the black? This is especially important for home cinema applications.
An average contrast ratio is about 400:1 for LCD projectors, whilst some DLP projectors have contrast ratio of 4000:1.
Keystone Correction
'Keystoning' is the name given to the effect on the projected image when the projector sits below or above the centre of the screen. Keystone correction counteracts this effect by digitally compressing the image at the bottom or top, resulting in a squarer, more professional image.
Lamp Hours
A standard lamp lasts for about 2000 hours of projecting. That's a lot of presentations, and with lamps sold at £150 and £:500, it works out at between 8p and 25p per hour of use. Projectors with higher lamp half lives are less likely to cause you a problem in the middle of a presentation when the projector gets older and used more, and generally represent better value per hour of use. However, with all projectors a sharp knock can put the lamp out of action no matter how old it is. Environmental factors can also effect lamp life so it's prudent to have a spare on hand.
Technology: LCD/DLP
DLP technology is a revolutionary display solution that uses an optical semiconductor to manipulate light digitally. It is a highly reliable, all-digital display chip that delivers the best picture across a broad range of products, including large screen digital TVs, and projectors for business, home, professional venue and digital cinema.
3LCD
3LCD is the most widely used projection technology system in the world. This is how 3LCD technology works: white light is split into red, green, and blue using two mirrors that transmit light with a certain wavelength.
Each colour is then passed through a dedicated LCD, before being combined with the other colors in a prism. The image is then ready to be projected onto the screen.
Lens Shift
Lens shift is generally a feature of high-end projectors or specialist home cinema models. Lens shift has a similar effect to 'Keystone correction' except that the effect is achieved by physically adjusting the angle of the projectors lens to square up the image. This is a better method of producing a square image, rather than using keystone correction as the correction with lens shift is achieved optically (rather than digitally) resulting in no loss of quality
Lens shift can also be useful for fine-tuning the position of the projected image on your screen
Ratio
In general, a ratio is a way of concisely showing the relationship between two quantities of something. The most formal way of stating a ratio is by separating the two quantities with a colon (:).
A ratio is a comparison of two numbers. We generally separate the two numbers in the ratio with a colon (:). Suppose we want to write the ratio of 4 and 3. We can write this as 4:3 (common ratio for data) or 16:9 (common ratio for video material)
Resolution
The resolution is the accuracy of the image that the projector casts. Most projectors fall into two categories - SVGA (800 x 600 pixels) or XGA (1024 x 768 pixels). Similarly, most computers output a signal which is either SVGA or XGA.
(Home cinema users - please note the majority of dedicated home cinema projectors project a native 16:9 (widescreen) image and fall into one of three resolution categories - WVGA (854 x 480 pixels), WSVGA (1024 x 576 pixels) or WXGA (1280 x 720 pixels). The 'W' stands for 'Wide'.
If you use a PC, you can check which signal you're using. Go to Control Panel and select 'Display', then click the Settings tab. Next to 'Screen Area' you'll see a slider which shows what resolution you're using. If it's 800x600, you use SVGA. If it's 1024x768, you use XGA. You can move this slider and press 'OK' to see the difference between the resolutions.
If you use a Mac, you can check which signal you are using by going to the 'Monitors', 'Displays' or 'Monitors and Sound' control panel (depending on which Mac OS version you are using).
Most projectors sold today are XGA. This is because most computers sold today are moving to XGA resolution as standard. You can project an SVGA output signal with an XGA projector without significant loss of quality. However, projecting an XGA signal with an SVGA projector can make your presentation look unsightly.
Response Time
The time it takes for a pixel to turn on and off. Response time is a good indication of how fast motion such as video or computer animation will appear on the projected image.
Weight
Are you taking your projector on the road or leaving it in the board room? If you are on the move, you'll appreciate having a projector that's as portable as you can afford. Thankfully, today's projectors are smaller than ever, with the lightest at around 0.9kgs and easy to carry over the shoulder. However, the desktop models still have more features and represent better value if the projector is going to stay in one place.
