Hello I suggest you use Raycasting to test if the camera is directly pointing to the light source. The ray will go from the camera into the front vector direction, Once you get the RaycastHit, you can check the name, the tag or even use Layer Mask to selectively ignore colliders.
If you want to apply the effect even when the camera is not pointing directly to the light, you can combine the test you are already doing to determine if the light is in view, and then raycast using the transform.LookAt(target) method to get a vector from the camera in the direction of the light. Please note that LookAt will rotate the transform, so do it with a new object that has the same values, or use Quaternion.LookRotation if you prefer.
Lastly you can improve using Vector3.Angle and Vector3.Distance to fine tune when to trigger the effect. Here is how you get the angle and distance assuming you have an array of all the lights on the view:
for( int i = 0; i < lightObjects.Length; i++)
Vector3 targetLine = lightObjects[i].transform.position - camera.transform.position; //Obtain the vector from camera to Target light
float distance = targetLine.magnitude;
float angle = Vector3.Angle (camera.transform.forward, targetLine); //Get the Angle between camera forwward and targetDir
if ( (distance < shortDistance && angle < 30) ||
(distance < mediumDistance && angle < 15) || (distance < longDistance && angle < 5f) )
Debug.Log("Apply effect on light " + lightObjects[i].name);
Debug.Log("Angle: " + angle.ToString () + " Distance: " + distance.ToString());