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

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

    // Get the LightType for given light fixture sybmol
    return LightType.GetLightType(document, lightSymbo.Id);
}

Public Function GetLightTypeFromLightSymbol(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 symbol first
   Dim collector As New FilteredElementCollector(document)
   collector.OfClass(GetType(FamilySymbol)).OfCategory(BuiltInCategory.OST_LightingFixtures)
   Dim lightSymbo As FamilySymbol = collector.Cast(Of FamilySymbol)().First()
   If lightSymbo Is Nothing Then
      ' check null reference
      Return Nothing
   End If

   ' Get the LightType for given light fixture sybmol
   Return LightType.GetLightType(document, lightSymbo.Id)
End Function