Method of controlling a motorized window treatment

1. A method of controlling a motorized window treatment for adjusting an amount of sunlight entering a space of a building through a window to control a sunlight penetration distance in the space, the method comprising:

measuring a total light intensity at the window;

determining if the total light intensity exceeds a cloudy-day threshold;

enabling a sunlight penetration limiting mode in response to determining that the total light intensity is greater than the cloudy-day threshold;

operating in the sunlight penetration limiting mode to control the motorized window treatment to thus control the sunlight penetration distance in the space, the sunlight penetration limiting mode causing partial opening of the motorized window treatment to a respective calculated position corresponding to each of a plurality of times so as to admit direct sunlight into the space within a predetermined maximum sunlight penetration distance from the window, such that the respective calculated sunlight penetration distance corresponding to each of the plurality of times is below the predetermined maximum sunlight penetration distance; and

disabling the sunlight penetration limiting mode in response to determining that the total lighting intensity is less than the cloudy-day threshold;

wherein the cloudy-day threshold varies with time during a first period after sunrise and during a second period before sunset, and is maintained at a constant threshold during a third period near midday.

2. The method of claim 1 , wherein the first period has a first predetermined duration and the second period has a second predetermined duration.

3. The method of claim 1 , further comprising:

controlling the motorized window treatment to a predetermined position when the sunlight penetration limiting mode is disabled.

4. The method of claim 1 , wherein the first period and the second period are respective periods when a calculated solar elevation angle is less than a predetermined solar elevation angle, and the third period is a period when the calculated solar elevation angle is greater than the predetermined solar elevation angle.

5. The method of claim 4 , wherein the cloudy-day threshold is a function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

6. The method of claim 5 , wherein the cloudy-day threshold is a linear function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

7. A system comprising:

a sensor for measuring a total light intensity at a window of a building; and

a processor configured for controlling a motorized window treatment for adjusting an amount of sunlight entering a space of the building through the window to control a sunlight penetration distance in the space, wherein the processor is programmed for:

determining if the total light intensity exceeds a cloudy-day threshold;

enabling a sunlight penetration limiting mode in response to determining that the total light intensity is greater than the cloudy-day threshold;

operating in the sunlight penetration limiting mode to control the motorized window treatment to thus control the sunlight penetration distance in the space, the sunlight penetration limiting mode causing partial opening of the motorized window treatment to a respective calculated position corresponding to each of a plurality of times so as to admit direct sunlight into the space within a predetermined maximum sunlight penetration distance from the window, such that the respective calculated sunlight penetration distance corresponding to each of the plurality of times is below the predetermined maximum sunlight penetration distance; and

disabling the sunlight penetration limiting mode in response to determining that the total lighting intensity is less than the cloudy-day threshold;

wherein the cloudy-day threshold varies with time during a first period after sunrise and during a second period before sunset, and is maintained at a constant threshold during a third period near midday.

8. The system of claim 7 , wherein the first period and the second period are respective periods when a calculated solar elevation angle is less than a predetermined solar elevation angle, and the third period is a period when the calculated solar elevation angle is greater than the predetermined solar elevation angle.

9. The system of claim 8 , wherein the cloudy-day threshold is a function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

10. The system of claim 9 , wherein the cloudy-day threshold is a linear function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

11. The system of claim 7 , wherein the first period has a first predetermined duration, and the second period has a second predetermined duration.

12. The system of claim 7 , wherein the processor is further programmed for:

controlling the motorized window treatment to a predetermined position when the sunlight penetration limiting mode is disabled.

13. An apparatus comprising:

at least one processor; and

a computer readable medium communicatively coupled to the at least one processor and having instructions stored thereon that when executed by the at least one processor direct the at least one processor to:

determine from a sensor measurement a total light intensity at a window of a building;

determine if the total light intensity exceeds a cloudy-day threshold;

enable a sunlight penetration limiting mode in response to determining that the total light intensity is greater than the cloudy-day threshold;

operate in the sunlight penetration limiting mode to control a motorized window treatment to thus control a sunlight penetration distance of sunlight entering a space of the building through the window, the sunlight penetration limiting mode causing partial opening of the motorized window treatment to a respective calculated position corresponding to each of a plurality of times so as to admit direct sunlight into the space within a predetermined maximum sunlight penetration distance from the window, such that the respective calculated sunlight penetration distance corresponding to each of the plurality of times is below the predetermined maximum sunlight penetration distance; and

disable the sunlight penetration limiting mode in response to determining that the total lighting intensity is less than the cloudy-day threshold;

wherein the cloudy-day threshold varies with time during a first period after sunrise and during a second period before sunset, and is maintained at a constant threshold during a third period near midday.

14. The system of claim 13 , wherein the first period and the second period are respective periods when a calculated solar elevation angle is less than a predetermined solar elevation angle, and the third period is a period when the calculated solar elevation angle is greater than the predetermined solar elevation angle.

15. The system of claim 14 , wherein the cloudy-day threshold is a function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

16. The system of claim 15 , wherein the cloudy-day threshold is a linear function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

17. The system of claim 13 , wherein the first period has a first predetermined duration, and the second period has a second predetermined duration.

18. The system of claim 13 , wherein the instructions, when executed by the at least one processor, further direct the at least one processor to:

control the motorized window treatment to a predetermined position when the sunlight penetration limiting mode is disabled.

19. A tangible, non-transient computer readable medium having instructions stored thereon that when executed by at least one processor direct the at least one processor to:

determine from a sensor measurement a total light intensity at a window of a building;

determine if the total light intensity exceeds a cloudy-day threshold;

enable a sunlight penetration limiting mode in response to determining that the total light intensity is greater than the cloudy-day threshold;

operate in the sunlight penetration limiting mode to control a motorized window treatment to thus control a sunlight penetration distance of sunlight entering a space of the building through the window, the sunlight penetration limiting mode causing partial opening of the motorized window treatment to a respective calculated position corresponding to each of a plurality of times so as to admit direct sunlight into the space within a predetermined maximum sunlight penetration distance from the window, such that the respective calculated sunlight penetration distance corresponding to each of the plurality of times is below the predetermined maximum sunlight penetration distance; and

disable the sunlight penetration limiting mode in response to determining that the total lighting intensity is less than the cloudy-day threshold;

wherein the cloudy-day threshold varies with time during a first period after sunrise and during a second period before sunset, and is maintained at a constant threshold during a third period near midday.

20. The system of claim 19 , wherein the first period and the second period are respective periods when a calculated solar elevation angle is less than a predetermined solar elevation angle, and the third period is a period when the calculated solar elevation angle is greater than the predetermined solar elevation angle.

21. The system of claim 20 , wherein the cloudy-day threshold is a function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

22. The system of claim 21 , wherein the cloudy-day threshold is a linear function of the calculated solar elevation angle when the calculated solar elevation angle is less than the predetermined solar elevation angle.

23. The system of claim 19 , wherein the first period has a first predetermined duration, and the second period has a second predetermined duration.

24. The system of claim 19 , wherein the instructions, when executed by the at least one processor, further direct the at least one processor to:

control the motorized window treatment to a predetermined position when the sunlight penetration limiting mode is disabled.