Does net curtain have a real impact on light?

I know it is a starnge question but a couple of years ago I was able to grow tomatos and a cucumber in a porch out front.  The last two years nothing and I was out clearing up and I realised it was 2 years ago the other half put up nets.  These are not a pattern just a very fine mesh (if I can get her to take them down no need for new fleece) could they reduce light levels that much?

I also put net curtains up for summer shade in the greenhouse with no problem