The BP_Spotlight_Follow Blueprint contains script in the EventGraph that makes it detect how far away the player's Pawn is and turn to face the Pawn when it comes within a specified Detection Range. The Hinge mesh component controls the spotlight's yaw, while the Spotlight mesh component only changes its pitch, which is clamped to prevent it from clipping through the hinge.
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The Find Look at Rotation node generates a rotation value when given a start location and an end location. The resulting rotation value can then be applied to a component located at the start location to make it face the end location. In this Blueprint, the start location is the spotlight's location, while the end location is the player Pawn's location. The Rotator value is broken apart, and the resulting Pitch and Yaw values are applied to the spotlight and hinge Static Mesh Components respectively.
Interpolation nodes, such as RInterp (for interpolating between two rotation values), are intended to feed values into nodes that are executed every frame, such as those connected to the ReceiveTick event or the Update pin on a timeline. Essentially, they blend smoothly from the Current Value to the Target Value based on the specified Interp Speed. For these nodes to work, a Delta Time value must be provided.
In this Blueprint, the Delta seconds variable is set from the Event Tick output. In this case, RInterp nodes are connected to Set World Rotation nodes to smoothly rotate the Spotlight mesh and Hinge mesh components, with a low Interp Speed so that the spotlight lags behind its target slightly.