Bright environment dimmers the screen

Hi green214,

Is your iPhone in a relatively warm area or direct sunlight when this happens? If so, it may be expected behavior. Your iPhone will dim its display as a way to regulate heat so it does not overheat or have to turn itself off.

See more info about how your iPhone may regulate its temperature below:

• Adjust the brightness and color temperature on your iPhone, iPad, or iPod touch - Apple Support

If your device gets too warm

iOS and iPadOS devices have built-in protections to prevent overheating. If the interior temperature of your device exceeds the normal operating range, your device will protect its internal components by attempting to regulate its temperature. Here are some of the higher ambient-temperature conditions and activities to avoid, because they might cause your device to change performance and behavior:

Avoid leaving your device in a car on a hot day.

Avoid leaving your device in direct sunlight for an extended period of time.

Avoid using certain features in hot conditions or direct sunlight for an extended period of time, such as GPS tracking or navigation in a car, playing a graphics-intensive game, or using augmented-reality apps.

If the interior temperature of your device exceeds the normal operating range, you might notice these changes:

Charging, including wireless charging, slows or stops.

The display dims or goes black.

Cellular radios enter a low-power state. The signal might weaken during this time.

The camera flash is temporarily disabled.

Performance slows with graphics-intensive or augmented-reality apps or features.

Additionally, if you're navigating, your device might show this alert and turn off the display: "Temperature: iPhone needs to cool down." Navigation still provides audible turn-by-turn directions. When approaching a turn, the display will illuminate to guide you through the turn.

Cheers!