What a phone screen is made of
A phone screen is a grid of tiny dots called pixels. Each pixel is made of smaller parts that produce red, green and blue light, and mixing those at different strengths creates every colour you see. The two panel technologies you will meet most often, LCD and OLED, differ in how that light is produced.
Over the glass sits a thin layer that senses touch. How that layer detects a fingertip is a topic in itself, covered in our piece on touchscreen technology. Here we focus on the part that produces the picture.
LCD: a backlight with filters
In an LCD, a backlight shines constantly behind the pixels. Each pixel contains a liquid crystal layer that twists to let more or less of that light through, and coloured filters turn the result into red, green or blue.
Because the backlight is always on, a dark pixel is really a pixel that blocks most of the light, and some leaks through. Blacks therefore tend to look slightly grey, particularly in a dark room. On the other hand, LCDs are mature, can be made affordably, and many are bright and colour-accurate. You will find them in a lot of budget and mid-range phones and in many tablets.
OLED: pixels that make their own light
In an OLED panel, each pixel produces its own light and can switch off entirely. That has several consequences.
- Blacks can be truly black, which gives high contrast.
- Dark themes can save a little battery, since dark pixels use less power.
- Panels can be thinner and can be made flexible, which is how curved and foldable screens are possible.
- Over very long periods, static images shown at high brightness can cause uneven ageing or faint image retention. This is uncommon in everyday use, and phones include measures to reduce it.
OLED tends to appear in higher-priced phones, but it has spread widely. Neither technology is automatically better in every situation: a well-made LCD can beat a poor OLED, so reviews matter more than the label.
Brightness and why it matters
Brightness is measured in nits. A higher figure means the screen can show a brighter image, which helps readability in sunlight. Manufacturers often quote two numbers: a typical figure for ordinary use and a higher peak figure that applies only to small bright areas, such as an HDR highlight, for short periods. These are not the same thing, so compare like with like.
Outdoor readability depends on more than raw brightness. Anti-glare coatings, how close the glass sits to the panel and automatic brightness all play a part. Also, running a screen near maximum brightness uses more battery and produces more heat, so adaptive brightness is usually the sensible default. Video and photo quality on the screen also depends on resolution and HDR support, a subject explored in our article on video resolution.
Resolution and sharpness
Resolution is the number of pixels, and sharpness depends on how closely they are packed. Past a certain point, extra pixels on a phone-sized screen are hard to see with the naked eye at a normal viewing distance. A higher resolution mainly costs battery and processing power, so a very high number on a small screen is not necessarily a practical advantage.
What a refresh rate is
The refresh rate is how many times per second the screen redraws the image. It is measured in hertz. A 60 Hz screen updates 60 times a second, which means a new frame roughly every 16.7 milliseconds. A 120 Hz screen updates 120 times a second, about every 8.3 milliseconds.
More frames per second means motion is shown in smaller steps. When you scroll a web page, the text moves in finer increments, and animations appear less jumpy. Many people notice the difference most when swiping through menus or reading while scrolling, and less when watching a film, because most video is recorded at a much lower rate than the screen can show.
Not everyone notices or cares. Some people see the improvement immediately, and others find 60 Hz entirely comfortable. It is a refinement, not a necessity.
Adaptive and variable refresh
Running at a high refresh rate all the time consumes more power. Many newer phones therefore use variable refresh rates, lowering the rate when you are reading a still page or watching a slow scene and raising it when you scroll or play a game. This helps battery life, though the saving varies from phone to phone. Some phones also let you choose a standard or high setting, and picking the lower one is a simple way to extend a day when the battery is struggling, which is also relevant when looking at battery health.
A high refresh rate also relies on the rest of the phone. The processor and software need to produce frames fast enough, otherwise the extra capability goes unused. An app or game limited to a lower rate will not look any smoother.
Choosing sensibly
When comparing screens, a short checklist works better than chasing the biggest numbers:
- Decide whether outdoor use is common, and check reviews of real-world brightness.
- Consider OLED if you often use the phone in the dark or enjoy video, but do not dismiss a good LCD.
- Treat a high refresh rate as a pleasant extra, particularly if you scroll a lot.
- Check how your own eyes respond. If possible, look at the screen in a shop under normal lighting.
For tablets and phones alike, the screen is the part you look at the most, so it is worth a few minutes of comparison, ideally alongside the other trade-offs in a general guide to choosing among mobile devices.