Paths with light effects are solid black

[RawRob]

I'm completely new with Illustrator.
I bought some EPS vector graphics files like this on iStock.

When I try to export them to PNG I get this.

I'm running the latest Illustrator on an old MacBook Pro.

I have searched high and low for an answer but found none.

Any help is greatly appreciated!

[Monika Gause · Accepted solution]

Please watch my youtube video: https://www.youtube.com/watch?v=Tiqm5hdQA5A

It explains how these files are built and why they look like that and don't work without a background.

[RawRob]

Thank you very much, this explains a lot! 
Quite irritating though that they won't move to modern file formats.
So whatever graphics/images I want to apply these glows to, I must import them into illustrator and use instead of the checkered background, right?
At least there's a solution then even if it's kinda cumbersome. 🙂 

[Monika Gause]

Those files will only work in Illustrator.

And you will have to place the background artwork behind the lights inside Illustrator.

[RawRob]

In order to not confuse other newbies who might be reading this thread...
From Illustrator you can then export the results with the added light/glow effects as PNG for example.
You just have to take that editing to Illustrator instead of doing it in Photoshop or whatever your app of choice is. 🙂