Add digital brains to a basic luminaire Outdoor lighting is usually switched on or off manually with a mechanical switch. Suppose, however, that you do not want to illuminate an area for the whole night. In that case, it would be advantageous to control the illumination more precisely so you can automatically switch the lighting off/on at a prescribed time.
A controller can sense ambient light, turn lights on when it gets dark, track a time interval, and automatically turn the lights off at a specified time. In the morning, the process can be reversed. If the ambient light level is under a preset lux threshold at a predetermined time, the system will turn on the light. It will turn the light off when the ambient gets bright enough to surpass the same lux threshold.
It is not difficult to design an intelligent lighting controller that senses and measures the ambient light level with an ambient light sensor (ALS). Equipped with a real-time clock (RTC), the controller also knows when to turn lighting on or off at specified times. The system presented here can be used to control all luminaires that are mains supply operated. The controller’s lux-level threshold is fully programmable in single-lux steps. Controller software is provided in hex format.
Integral system components The lighting controller in this design needs to measure the ambient light level which is done with an ALS. There are two different kinds of ALS products in the market today: one outputs the analog voltage proportional to the ambient light level, and the other gives the output in digital format. This system uses the ALS with the digital output.
The controller needs to know the exact time, so a real-time clock (RTC) is used. To anticipate possible power loss, the time information needs battery backup.
A user interface is needed for setting time and other parameters. The user interface here consists of two 7-segment LED displays and one pushbutton. With a short button press, the system displays time and other parameters. With a long button press, the time and parameters can be adjusted.
The system has an auto/manual switch to enable switching the light on or off manually.
System power comes from the mains supply. Electricity to the luminaire is switched on/off through a relay. The digital portion of the system is isolated from mains supply.
The system block diagram is shown in Figure 1.
Figure 1: Lighting controller system
Figure 2 further illustrates the system wiring to the mains supply voltage and to luminaire(s).
Figure 2: System wiring to the mains supply voltage and to luminaire(s)
When the system is used in manual mode, the auto/manual switch must be switched to manual. In manual mode, the relay is continuously on and the luminaires are switched on/off using a standard wall light switch.
When the auto/manual switch is in auto mode, the standard wall light switch must be switched on so the controller can function. If that wall switch is not on, the controller cannot switch the luminaires on.
Seems like the value added from a utility perspective is little in comparison to many solutions that already exist there (many solar lights for gardens and walkways switch on automatically, albeit without a real time clock). If cost of adding ALS changes the lighting solution cost, it may not be worth it. I can get a timer for multiple circuits and control on-off times (the XMas tree controllers for example).
About 10 or 12 years ago I built a lighting control system with similar function for an office building I own. I used a timer and photocell from the local home improvement store. The photocell was wired in series with the timer switch contacts. The result is that the lights come on at sunset, shut off at 11:00pm, come on at 5:00am and shut off again at sunrise. The clock is mechanical so it is adjusted the old fashioned way and the photocell sensitivity is adjusted with a little black tape partially blocking the sensor. Not as sophisticated as your micro-controller but it has worked for years with little maintenance other than new light bulbs and resetting the clock after a power failure.
@wb9ddf: thank you for reinforcing my point with more detailed explanation. To be fair to the authors, there may be some value-added uses cases (perhaps industrial ones) in controlling lux-level threshold but its case hasn't been made adequately in the article.
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