Hi ceemimi,

The openness is only one factor to consider I how much light will be allowed into the room. The color and density of the fabric makes a considerable difference as well. A dark, thick fabric will not transmit light the way a lighter colored, thinner fabric will. A lighter fabric will "illuminate" the room much more than a dark fabric will.

Typically, "openness" describes solar shades, a variation of roller shades. I would recommend having some material samples in the windows you are looking to cover so that you can see how openness and fabric choice will work in that space.

Thanks for your response. I did see a sample, but it was just a small swatch, so it's hard to imagine the difference between 3% and 5%. Is there a big difference between the two percentages?

In terms of how much light enters the room,, if the fabric is a lighter color, not really. If the fabric is a darker coler, the 5% will let in more light, but not drastically more. The bigger difference will be in how much you'll be able to see outside during the day and how much privacy they will provide at night. Even with this, shade color makes a difference. Darker colored materials allow a more defined view than lighter colored materials with the same openness factor (see image).

http://www.yourblinds.com/s/YB/images/categoryOverview/Solar_whiteBlack_All.jpg

Thank you! That really broke it down and the pic was helpful.

We have a nice chart to explain openness factors. You can see it at http://www.solar-screen-shades.com