Lighting effect changing image quality

[JosephWhittle]

Hi all
New poster here, have an urgent issue I can't seem to solve.

I have a PNG which I want to add a simple light effect to to give it a bit of texture. But when I apply a spotlight to it, the quality of the image drops drastically - I cannot see how to change this setting (or even if it is a setting).

I'm not a PS user usually. What am I doing wrong?

edit - the pictures below don't show the effect very well. Essentially after applying the lighting it looks like I've whacked the resolution right down.

 

[gedstar]

Hi and Welcome to PSG

What method are you using to apply the spotlight effect?

 

[JosephWhittle]

Hello!
The method is filter > render > lighting effects. Its a white point light I'm using on a flat png image.

 

[gedstar]

Hi

I haven't been able to replicate what you're seeing, that been said I don't know what settings you're using so it may be helpful if you could provide a screenshot of the Lighting Effect settings
Whether saving as JPEG or PNG does not effect the resolution on the your image that I tried

 

[Tom Mann]

Also, please post the original png file. If it is too large for the forum's uploader, either zip it and post the zip file, or if that is too large put it on dropbox or any of the usual file sharing sites and post the link.

Thanks,

Tom M