How to use Shader Nodetree in emissions rendering? I am trying to render my image using a point light source. Now, I want to increase the brightness using node emissions. But, when I do so, I get an error. I have read the related questions here, but my problem is the of a point light source, not sun or material as before. 
Attached are the parameters what I want to change and the error message.

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I am using this line of code:
    bpy.data.node_groups["Shader Nodetree"].nodes["Emission"].inputs[1].default_value = 10000

Thank you so much! :)
In bpy.data.node_groups you will find node groups that you have made, that is nodes that you have turned into a group that you can use in multiple materials.

The nodes for a light can be found in the lights data property.

light_nodes = bpy.data.objects['lamp1'].data.node_tree.nodes
light_nodes['Emission'].inputs['Strength'].default_value = 10000