Hi Geth270,
The reason is that emission is not a variable but a property I think. Most parts of Unity are not open-source, so this is just a guess. In your script editor, hover the mouse cursor over emission to see if you get more information.
If emission is a property, it might be that only the get part is implemented. This means that emission is actually a method returning a value. We cannot assign anything to a method. And that’s why the second piece of code does not work.
Did this clear it up for you?
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