US 6,084,231 · Granted 2000-07-04
The Smart Window Blind That Ignores Artificial Light
Imagine window blinds that automatically open and close based on how much real sunlight is coming in—but they completely ignore the light from indoor lamps so they don't get confused. This patent describes a sensor that can tell the difference between daylight and artificial light, letting your blinds respond only to the sun.
The plain-English version
What it protects
The claim covers a closed-loop system that automatically adjusts window coverings in response to natural daylight while remaining insensitive to artificial lighting from fluorescent or similar lamps. What's protected here is specifically the combination of a sensor that detects infrared wavelengths (800-1200 nanometers) where daylight is strong but fluorescent light is absent, a control unit that processes that sensor signal, and motorized shading that physically adjusts based on that processed signal. The innovation is the spectral filtering that allows the sensor to distinguish sun from indoor bulbs.
Why it matters
This patent solves a real problem in modern offices and homes: automatic blinds that kept closing when you turned on the lights because they couldn't tell the difference between sunlight and lamp light. By tuning the sensor to infrared wavelengths that daylight contains but fluorescent lamps don't emit, the system becomes truly independent of artificial lighting. This matters for energy efficiency, comfort, and the reliability of automated building controls in mixed-light environments.
Real-world use
In an office with both windows and overhead fluorescent lighting, these smart blinds would gradually close as afternoon sun gets stronger—but wouldn't suddenly shut when someone flips on the lights in the afternoon.
Original USPTO abstract
A system for automatic regulation of daylight admitted by a window in the presence of artificial illumination produced by a high-efficiency (e.g., fluorescent-type) electric lamp. A preferred embodiment, adaptive window covering system 10, consists of an illuminance sensor 11, a conventional control apparatus 12, and a conventional shading means 13. System 10 is used in conjunction with a conventional, high-efficiency, electric lamp 14 and a conventional window 18, in a room 19. Sensor 11 produces a signal dependent on power contained in a portion of the daylight spectrum, but substantially insensitive to power contained in the spectrum of artificial illumination produced by lamp 14. In a preferred embodiment, sensor 11 includes a silicon photodiode and optical low-pass filter to provide a spectral response which extends from approximately 800 to 1200 nanometers, which falls outside the spectrum produced by typical fluorescent lamps (e.g, 300 to 750 nanometers). Sensor 11 is oriented to sample the ambient illumination in room 19, which includes both daylight and artificial components. Control apparatus 12 produces an actuating signal dependent on the output of sensor 11. Shading means 13 varies the amount of daylight admitted by window 18 as a function of the actuating signal produced by control apparatus 12. Thus, system 10 varies the amount of daylight admitted by window 18 as a function of the power contained in a portion of the daylight spectrum, but independent of the power contained in the spectrum produced by lamp 14.
Patent details
- Publication number
- US 6,084,231
- Filing date
- 1997-12-22
- Grant date
- 2000-07-04
- Assignee
- Popat; Pradeep P.
- Inventor(s)
- POPAT; PRADEEP P.
- CPC class
- E06B9/32
Want to file your own patent?
If you're developing a home-automation product that needs to sense real daylight without false triggers from indoor lights, explore how sensor spectral response works before filing your own patent application.
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