Incident and reflective light metering are two methods used in photography to measure the amount of light that falls on a subject or scene. Here's how they differ:

Incident light metering: This method measures the amount of light falling on the subject itself, rather than the light that's reflected by the subject. Incident light metering is done by placing a light meter close to the subject and pointing it towards the camera. The meter measures the amount of light falling on the subject and gives a reading based on that. This method is particularly useful for situations where the subject is backlit or there are large variations in lighting across the scene.

Reflective light metering: This method measures the amount of light reflected by the subject or scene. This is the most common type of metering used in cameras. In this method, the camera's light meter measures the light reflecting off the scene or subject and calculates the exposure settings accordingly. Reflective light metering is effective for most situations, but can lead to underexposure or overexposure if the scene is particularly bright or dark.

Both incident and reflective light metering have their advantages and disadvantages depending on the specific lighting conditions and the desired outcome. It's important for photographers to understand both methods and choose the appropriate one for the situation.