A general rule of thumb is that an orchid should be a green like a lime rahter then the green of a cucumber. The lime color requires a bit more light and it will help your orchids bloom. If you have not had your orchids bloom for you in a few years try to increase the light level slowly. If you start to see the leaves turning dark or looking a tad brown then immediately reduce the light or your plant will have a case of sunburn.
We have one side with the plastic seen on the greenhouse page and a second side with the plastic and a 40% shade cloth for the Phalaenopsis, Paphiopedilums and the seedlings to grow.
With an SLR Camera set to ASA 200 and set to f-4.0
9:00 AM clear 1/60th
Noon Clouded but greenhouse in sun 1/250
A lot of the positioning of your plants would depend on the part of the country you live in. We would suggest a South window with a curtain that would be similar to a white cloth shower curtain. The best choice would be a white curtain that allows a good amount of light to come trough.
For lighting your orchids; imagine the equivalent to being about 1/2 way up a tall oak tree. Most people grow orchids hanging in the low branches of an oak tree and they do very well in that setting.
Please take a look and let me know the type of orchid you have. Many will require less filtered light. For the most part you want to give them plenty of light but not direct sunlight. Direct light will cause the plant to get sunburned. We have had a plant light set up in the house that caused some sunburns so it truly would depend on the type of orchid you have.
Please keep in mind that a plant dries out much faster in the house then it does outside.