I have been trying find an answer to this question for a very long time but I still haven't! "How to add light sources in the gazebo world dynamically ?" I am using ROS-Groovy (Gazebo 1.5.0).

In electric (pre-1.0 SDF) there was this <model:renderable> option where I was able to spawn light source as a model after launch the gazebo world in any pose I wanted.

<?xml version="1.0" ?>
<robot name="light_balcony">
  <link name="bulb_balcony">
   <inertial>
    <mass value="1" />
            <com xyz="11.27 3.15 2.25" />
            <inertia ixx="0" ixy="0.0" ixz="0.0" iyy="0" iyz="0.0" izz="0" />
        </inertial>

        <visual>
            <origin xyz="11.27 3.15 2.25" rpy="0 0 0" />  <!--   definition of the visual postion of the object!! -->
            <geometry>
                <sphere radius="0.0001" />
            </geometry>
        </visual>
        <collision>
            <origin xyz="11.27 3.15 2.25" rpy="0 0 0" />
            <geometry>
                <sphere radius="0.0001" />
            </geometry>
        </collision>
    </link>

    <gazebo reference="bulb_balcony">
        <model:renderable name="light_balcony">
            <xyz>11.27 3.15 2.25</xyz>
            <static>true</static>
            <light>
                <type>point</type>
                <diffuseColor>0.1 0.1 0.1</diffuseColor>
                <specularColor>.01 .01 .01</specularColor>
                <attenuation>0.1 0.1 0.0001</attenuation>
                <range>4</range>
            </light>
        </model:renderable>
    </gazebo>
</robot>

When I switched to fuerte, it was no longer an option and even in groovy, I am not able to find a way out :( I am able to add a light to my world file but what I really want is adding it dynamically similar to adding a model. Taking advice from @AndreiHaidu and others (here, and many other pages), I tried a lot like adding

<include>
        <uri>model://sun</uri>
        <pose>0.3 0.2 5.0 0 0 0</pose>
    </include>

or

<light type="directional" name="my_light">
            <pose>0 0 30 0 0 0</pose>
            <diffuse>.9 .9 .9 1</diffuse>
            <specular>.1 .1 .1 1</specular>
            <attenuation>
                <range>20</range>
            </attenuation>
            <direction>0 0 -1</direction>
            <cast_shadows>true</cast_shadows>
        </light>

I have tried these in different sdf formats too. All threw errors. Finally when I tried this,

    <gazebo version='1.0'>
    <model name='apartment_floor0' static='1'>
     <origin pose='-5 -5 0 0 0 0'/>
       <link name='ow_2_body' gravity='1' self_collide='0' kinematic='0'>
            <origin pose='0 0 0 0 0 0'/>
            <collision name='ow_2_geom' laser_retro='0.000000'>
              <origin pose='3.300000 0.150000 1.500000 0.000000 -0.000000 0.000000'/>
              <geometry>
                <box size='2.400000 0.300000 3.000000'/>
              </geometry>
              <surface>
                <friction>
                  <ode mu='-1.000000' mu2='-1.000000' fdir1='0.000000 0.000000 0.000000' slip1='0.000000' slip2='0.000000'/>
                </friction>
                <bounce restitution_coefficient='0.000000' threshold='100000.000000'/>
                <contact>
                  <ode soft_cfm='0.000000' soft_erp='0.200000' kp='1000000000000.000000' kd='1.000000' max_vel='100.000000' min_depth='0.001000'/>
                </contact>
              </surface>
            </collision>
            <visual name='ow_2_geom_visual' cast_shadows='1' laser_retro='0.000000' transparency='0.000000'>
              <origin pose='6.850000 1.500000 1.500000 0.000000 -0.000000 1.570800'/>
              <geometry>
                <box size='2.400000 0.300000 3.000000'/>
              </geometry>
              <material script='Gazebo/White'/>
            </visual>
          </link>
    </model>     
 <light name='my_light' type='directional'>
      <pose>0.000000 0.000000 30.000000 0.000000 0.000000 0.000000</pose>
      <diffuse>0.900000 0.900000 0.900000 1.000000</diffuse>
      <specular>0.100000 0.100000 0.100000 1.000000</specular>
      <attenuation>
        <range>20.000000</range>
      </attenuation>
      <direction>0.000000 0.000000 -1.000000</direction>
      <cast_shadows>0</cast_shadows>
    </light>
</gazebo>  

I did not get any error but I was only able to see the ow2body on the world and the light did not appear at all.

Is there any mistake I am doing that I am not seeing ? Is there any other way out or should I accept the cold truth that there is no way out ?

I repeat, I don't want to spawn it with the world, I want to spawn it as model after launching gazebo world. I am using ROS groovy now with gazebo 1.5 and I also have a standalone gazebo 1.8 installed.

Thanks,

Prasanna