love.graphics.getPixelHeight
Gets the height in pixels of the window.

The graphics coordinate system and DPI scale factor, rather than raw pixels. Use getHeight for calculations related to drawing to the screen and using the coordinate system (calculating the center of the screen, for example), and getPixelHeight only when dealing specifically with underlying pixels (pixel-related calculations in a pixel Shader, for example).
pixelheight = love.graphics.getPixelHeight()
pixelheight number The height of the window in pixels.