How directional light managed?

[younggam]

What I expected from DirectionalLight is that I could see the object under light, then reflection.
But, actually what I saw in application is
a light point(bulb) reflection and either the reflection of light is completely invisible or visible depends on angle between camera rotation and light rotation.

How I could use it as what I expected?
or any other alternatives?

DirectionalLightBundle {
            directional_light: DirectionalLight {
                illuminance: 33333.0,
                shadows_enabled: true,
                ..default()
            },
            transform: Transform::from_xyz(0., 0.1, 0.).with_rotation(Quat::from_euler(
                EulerRot::ZYX,
                0.,
                std::f32::consts::PI * 0.,
                std::f32::consts::PI * -0.25,
            )),
            ..default()
        }

note that if light's rotation is much parallel or perpendicular to XZ plane, it doesn't reflect anything
and also, the reflection of light was not applied to all plane objects on the XZ plane

[younggam]

I'm ashamed, but this is my bad. I attached mesh and material components to light, and they caused unexpected behaviours.