Reality, most of those areas are likely unsuitable for the vast majority of plants without supplementary lighting. Other plants may survive but not thrive. "Eyeing it" is a notoriously crappy method for determining light quality for plants. The issue, simply put, is that the amount of light needed for our eyes to see by is FAR less than the amount required by plants for photosynthesis. So, no, just because an area LOOKS bright to our eyes, does not mean it is bright enough from a plant's viewpoint.

A simple, rough way to estimate whether an area is bright, medium, or low light:
*Bright -- hand placed a foot above the plant between the plant and the light source casts a dark, sharp-edged shadow on the plant.
*Medium -- hand placed a foot above the plant between the plant and the light source casts a lighter, soft/blurry-edged shadow on the plant.
*Low -- hand placed a foot above the plant between the plant and the light source casts no discernible shadow on the plant. Because this last one covers such a broad category, the risk of low being too low even for a "low light plant" is very real.

Keep in mind the above is just for a rough estimate. The only accurate method for determining light intensity is with a light meter.

Also there is the issue of light spectrum. Color spectrum and Kelvin ratings (color temperature) are used to determine plant quality lighting. Incandescent lights for example are not suitable for plants -- their color spectrum is not a good match for a plant's needs. (Also they give off a great deal of heat.) I'll let the more learned cover that .

As far as distance is concerned, the further from the light source, the weaker the light. Light follows an inverse square law. So a plant that is 2 feet from the light source, only receives 1/4 the light as a plant that is right by the source. A plant that is 4 feet away only receives 1/16 the amount of light. Put simply, light intensity falls off to useless levels very quickly.

Plant-wise your selections for non-window areas will likely be extremely limited. Consider the plants one sees in a mall. Typically the only things one sees are pothos, peace lilies, or Sanseveria. These plants can survive very low light but they do not THRIVE under such conditions. Furthermore, what the average person does not realize, is that any said mall plants that begin to fail are quickly replace with new plants by the florist/nursery which maintains the plants for the mall. Doing so maintains the illusion that the plants are doing well there.

Plants "see" light differently than human beings do. As a result, lumens, lux or footcandles should not be used to measure light for plant growth since they are measures used for human visibility. More correct measures for plants are PAR watts, PPF PAR and YPF PAR, although each in itself does not tell the whole story. In addition to quantity of light, considerations of quality are important, since plants use energy in different parts of the spectrum for critical processes.

As a general rule of thumb I look for 50 foot candles as a minimum. White walls help, and mirrors. If I were you I'd just buy a few things as an experiment and see how they do. I have several rooms facing north and I have had the following survive the one year mark:

Peace lily (no flowers, of course)
Chinese evergreen (Alaonemas)
Snake plants (Sansevierias)
Aspidistra
Dracaena fragrans "Janet Craig" (looks like a solid green corn plant)
Pothos

In some cases you might have to remove spindly new growth to maintain the look of the plants. You'd be better off buying the plants at the full size that you want since they will not grow well. Also remember they need very little water in low light. I lift the pots up to see if they feel light.

Edit: Oh yeah, and look for the solid green leafed varieties, or at least as much green as possible. They have more chlorophyll and thus can survive the lower light better.

This post was edited by eaksqueak on Sat, Nov 29, 14 at 10:46

thanks so much ill give it a try. And as far as the shadow test goes if I find a spot ANYWHERE in the room that looks bright, as long as I do that white paper shadow trick and judging by the shadow given on it I can grow the appropriate plant according to shadow? (say for example far into a room I try the shadow trick and I get either a well defined shadow meaning high light I can grow a cactus there? or if its a moderate shadow anywhere in the room I can grow a medium light plant there?

I'm sure there must be exceptions, but most cacti are going to need direct sunlight. I have some in a south facing bay window and they still look kind of tall and stretched anyway, probably because I live in Pennsylvania and it's overcast half of the time.

If you're interested in succulents check out a group of plants called Haworthias. They somewhat resemble aloes, but are more low light tolerant. I found a number of different varieties at Ikea of all places.

I can cast ( with no clouds in the sky VIA paper test)shadows on a wall 45 feet away today, A fewt short weeks weeks from now that same shadow won't reach 30 feet, early spring it wont be seen or be solid at 10 feet away.
By summer todays paper test shadow 45 feet away wont be seen at a few short inches away from the same window becuse the sun is earlier and quicker to rise and is to high in the sky from 9:15-11: 30 AM the time when todays hard shadow is seen.