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In Unreal Engine 5, you can create an emissive material by using the Emissive Color input on the Material instance. Here's how you can do it:

Create a new Material in the Content Browser by right-clicking and selecting "Material" from the context menu.

In the Material Editor, you can set the Emissive Color by clicking on the "Emissive Color" input and choosing a color from the color picker.

To control the intensity of the emissive color, you can use the "Emissive Strength" input. This value is multiplied with the emissive color to give the final emissive output.

If you want the emissive color to only affect certain parts of the material, you can use a texture mask. To do this, you can use the "Emissive Mask" input and connect it to a texture sample node.

To make the material actually emit light, you need to enable "Emissive" in the "Material Domain" dropdown.

Finally, you can use the "Emissive Color" and "Emissive Strength" outputs in the Material Graph to control the emissive properties of the material.

I hope this helps! Let me know if you have any questions.