The only way to judge natural lighting in a house is to go there at different times of the day and at different days of the year. Houses rarely stay on the market that long (but in this market ...) and realtors might get annoyed at the 10th or 20th showing. In general, if you like the house in winter, you'll probably like it in summer. Also, in our Northern Hemisphere, and in these Northern latitudes "South Facing" is a good bet. The sun spends most of its time shining from the south east to the south west and those are the rooms that get most of the sun.
There are a few tools, however, that can give you an idea of sunlight in a location. One of these is NOAAs Solar Calculator. This website allows you to see the direction of the rising and setting sun for different dates. You can't enter an address directly and you have to zoom in to your location. Another tool that looks remarkably like NOAA's calculator but allows you to put in an address directly is Vladimir Agafonkin's SunCalc. I used both these tools to get an idea of where the sunlight would be at different seasons. This, of course, does not give you an idea of the brightness of a room, which depends on the foliage outside, the color of the neighboring buildings and the color of the interior walls.