There are times when you don't want your smartphone's screen to automatically dim after a few seconds -- working from a recipe, showing off photos, studying your social media strategy -- but there's no way to do this natively on stock Android (the most you can extend the delay to is 30 minutes). If you need your display on permanently until you manually lock it, then there are apps and tweaks to help.
All of the good-quality apps on Google Play built for this task offer a different selection of options. We tested Keep Screen On, Stay Alive and Wakey (if there are better ones, let us know) and it's difficult to choose between them as they all have their pros and cons -- you'll have to find something that best suits your way of working. We'd probably pick Wakey if pushed, as the basic functionality is simple, streamlined and free.
Keep Screen On (above) is free to use but the developer asks for donations if you find it helpful on a regular basis. There are some handy options here, including a proximity sensor, app-by-app settings and the ability to keep the screen on while your device is charging.
While it's not quite as polished and user-friendly as the alternatives, the fact that you can use all of its features for free means it's an appealing choice -- we'd recommend stumping up some cash to support the app if you use it long term, but you can at least try out everything before you buy.
Stay Alive (above) offers an impressive number of options for free plus some extra bells and whistles if you donate. Without paying you can keep the screen on indefinitely, configure app-by-app settings and have the program disable itself if your battery reaches a certain point.
Chip in some money and you get features such as a solid black, tap-to-wake lock screen alternative, auto-start on boot functionality and the option to disable the app based on your proximity. Everything you're likely to need is in the free edition though the app is slightly unusual in that you access it from the notification drawer.
Wakey (above) does the basic job of keeping your screen on for free: Just tap the bulb inside the app and the screen won't dim until you tell it to. There's also a timer and dimming option in the free version. It strikes a good balance between ease-of-use and functionality and if you just need a toggle switch then it's the best one to go for.
For a few pennies more you can add features like autowake (keeps the screen alive automatically when certain apps are running), chargewake (keeps the screen alive while the device is charging) and CPU wake (where background tasks aren't interrupted).
Finally, stock Android does have a hidden setting to keep the screen on indefinitely, but only while charging. You need to activate Developer Mode first (tap the Build number entry in the About phone menu in Settings seven times) and then choose Developer options from the Settings menu. Choose Stay awake and as long as your phone or tablet is plugged in, the screen won't go to sleep after a certain period of time.