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This lesson covers the main output devices required by the OCR H446 specification: monitors, printers, speakers and actuators. For each device you must understand how it works, its advantages and disadvantages, and when each type is appropriate.
An output device is any hardware that converts processed digital data from a computer into a form that humans can perceive (visual, audible, physical) or that affects the physical world.
A monitor (or display) is the primary visual output device. There are several technologies:
| Aspect | Detail |
|---|---|
| How it works | A backlight shines through layers of liquid crystal and colour filters. Applying an electric current to specific pixels causes the liquid crystals to twist, allowing more or less light through. Each pixel has red, green and blue sub-pixels |
| Advantages | Thin and lightweight, low power consumption, no flicker, widely available, affordable |
| Disadvantages | Limited viewing angles (TN panels), slower response times than OLED, blacks are not truly black (backlight bleeds through) |
| Variants | TN (Twisted Nematic — fast but poor angles), IPS (In-Plane Switching — better colour and angles), VA (Vertical Alignment — good contrast) |
| Aspect | Detail |
|---|---|
| How it works | Each pixel is made from an organic compound that emits its own light when an electric current is applied. No backlight is needed |
| Advantages | True blacks (pixels can be completely off), excellent contrast ratio, wide viewing angles, thin and flexible, fast response times |
| Disadvantages | More expensive to manufacture, risk of burn-in (permanent ghost images from static content), shorter lifespan than LCD for some uses |
| Common use | Smartphones, high-end TVs, smartwatches |
| Feature | LCD | OLED |
|---|---|---|
| Backlight | Yes (always on) | No (self-emitting pixels) |
| Black levels | Grey (light leaks through) | True black (pixels off) |
| Contrast | Lower | Higher |
| Power (dark content) | Same as light content | Lower (fewer pixels lit) |
| Viewing angle | Varies (TN poor, IPS good) | Excellent |
| Burn-in risk | No | Yes |
| Cost | Lower | Higher |
| Lifespan | Longer | Shorter (organic materials degrade) |
| Term | Definition |
|---|---|
| Resolution | The number of pixels on the screen (e.g. 1920 x 1080 = Full HD, 3840 x 2160 = 4K UHD). Higher resolution = sharper image |
| Refresh rate | How many times per second the screen redraws the image (measured in Hz). 60 Hz is standard; 144 Hz and 240 Hz are used in gaming for smoother motion |
| Response time | How quickly a pixel can change colour (measured in ms). Lower is better for fast-moving content |
| Aspect | Detail |
|---|---|
| How it works | Tiny nozzles spray microscopic droplets of liquid ink onto paper. The print head moves back and forth across the page. Ink is typically CMYK (Cyan, Magenta, Yellow, Key/Black) |
| Drop methods | Thermal: a heating element vaporises ink to create a bubble that forces a droplet out. Piezoelectric: a crystal vibrates to push ink out of the nozzle |
| Advantages | High-quality colour printing, good for photos, relatively cheap to buy, quiet operation |
| Disadvantages | Ink cartridges are expensive (high running cost), prints can smudge when wet, slower than laser for bulk printing, nozzles can clog if not used regularly |
| Best for | Home use, photo printing, low-volume colour printing |
| Aspect | Detail |
|---|---|
| How it works | 1. A laser draws the page image onto a rotating photosensitive drum by changing the drum's electrical charge in specific areas. 2. Toner (fine powder) sticks to the charged areas of the drum. 3. The toner is transferred from the drum onto the paper. 4. A fuser (heated roller) melts the toner into the paper, making it permanent |
| Advantages | Fast printing speed, low cost per page, sharp text, prints do not smudge, reliable for high-volume use |
| Disadvantages | More expensive to buy (especially colour laser), bulkier than inkjets, toner replacement is costly, not ideal for high-quality photo printing |
| Best for | Office use, high-volume document printing, text-heavy documents |
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