First of all. If you ever feel that you need to use Get All of Something nodes, you’re making a mistake in 99.99% cases. It has its uses but avoid using it unless you understand what it does and what it’s used for best. It leads to bad practices if used for getting references.
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So you call Create Widget in the Level Bleurpint and the lamps are in the level as well. In this case it’s all fairly straightforward:
https://forums.unrealengine.com/core/image/gif;base64
You do not need to do anything in the widget. Remove whatever your buttons do. And instead implement the above.
You can get a reference to your Lamp by selecting it in the scene and drag-dropping it into the graph; or select in the scene and right click in the graph -> Create Reference to Lamp. The above will bind the button’s onClick event and let it toggle the light.