One potential cause of a screen flickering is a problem with the firmware that regulates the MacBook's screen and graphical processing hardware, or software glitches with the operating system's display capabilities. When Apple's software engineers encounter these problems, they release software updates to resolve them. Users should regularly check for updates to ensure that they're using the most software.
Apple's MacBook laptops have sensors to detect the level of ambient light around the device. This equipment allows the computer to automatically adjust its display brightness as the light around the user changes. By increasing or decreasing brightness in reaction to decreasing or increasing light around the device, the user will not notice any change in how bright he perceives the screen to be. If this detector malfunctions, then it could change the screen's brightness level incorrectly and erratically. Performing a system update could fix the problem.
At times, display flickering may derive from defects in the System Management Controller. The SMC is a piece of hardware that regulates many basic processes within the MacBook, but internal errors on the controller can cause irregular behavior on the laptop. This irregular behavior can include display flickering. If an internal error with the SMC is causing the problem, then resetting the SMC can resolve the issue. Users can do this by simultaneously pressing down the left hand "Shift" key, "Control" key, "Option" key, and "power" button while the power cord is plugged into the laptop. Proceeding to release all these keys at the same time will reset the SMC.
While updates or resetting the SMC could fix software-based problems, physical defects in the light sensors or the screen cannot be resolved by the user alone. These would require a technician to open up the laptop's body to look for signs of defects or damage. Because of the complexity of modern computer hardware, most damaged components must be replaced. Sensors and screen hardware are covered under Apple's basic warranty, so if the customer brings the defective laptop into one of Apple's Genius Bars, and the computer is still under warranty, these repairs will be free.