Grid Effect

Open the document that you want the grid on. Here I have a beautiful picture of our Parliament Buildings in Ottawa.

Find the Channels Palette and make a new layer.

Zoom in (Ctrl + "+") to 1600% and taking your Pencil size 1px draw a small line going horizontally and then an other going vertically. Make them about three pixels wide each.

Grabbing your Rectangular Marquee select the box like in the image to your left.

Next go Edit > Define Pattern and give your pattern a name. Now delete the Channel layer you were just on and make a new one and zoom out (Ctrl + "-").

Grab your Fill tool and make sure the Fill is on pattern with the pattern you just made selected (check the top of your window.. there's a drop down menu). Fill your Channel layer.

Still in your Channels Palette select the Load channel as selection and change over to your Layers Palette.

Make a new layer.

With the colour that you want for your scanlines in the foreground, press Atl + Backspace. This should fill the marquee selection with colour. In this case, it is black. Deselect (Ctrl + D).

This next part is to your preference. You can lower the Opacity, or blur the lines using Filter > Blur > Gaussian Blur. You can also play around with the Blending modes until you get something you like. Don't forget though that you can make the square bigger or smaller; try doing one with a 5x5 pixel or even a 8x8 pixel.

Here I used Yellow (F7D808) as the colour and I set the Blending mode to Multiply. I then dropped the Opacity down to 47% and added some text.