public LightType GetLightTypeFromLightInstance(Document document)
{
    if(document.IsFamilyDocument) // not used in family document
        return null;

    // In order to get the light infromation, please get a light fixture instance first
    FilteredElementCollector collector = new FilteredElementCollector(document);
    collector.OfClass(typeof(FamilyInstance)).OfCategory(BuiltInCategory.OST_LightingFixtures);
    FamilyInstance lightFixture = collector.Cast<FamilyInstance>().First<FamilyInstance>();
    if (lightFixture == null)    // check null reference
        return null;

    // Get the LightType for given light fixture
    return LightType.GetLightTypeFromInstance(document, lightFixture.Id);
}

Public Function GetLightTypeFromLightInstance(document As Document) As LightType
   If document.IsFamilyDocument Then
      ' not used in family document
      Return Nothing
   End If

   ' In order to get the light infromation, please get a light fixture instance first
   Dim collector As New FilteredElementCollector(document)
   collector.OfClass(GetType(FamilyInstance)).OfCategory(BuiltInCategory.OST_LightingFixtures)
   Dim lightFixture As FamilyInstance = collector.Cast(Of FamilyInstance)().First()
   If lightFixture Is Nothing Then
      ' check null reference
      Return Nothing
   End If

   ' Get the LightType for given light fixture
   Return LightType.GetLightTypeFromInstance(document, lightFixture.Id)
End Function