Leaving lights on at full blast for all hours of the night can be wasteful, especially when there are no people around to benefit from that light. Energy is wasted, and checkbooks run thin when it is time to pay the bills. Our idea is to design a system of motion sensor lights that also have a dimming function based on sensed light. The motivations of examining this process are energy and cost reduction. Both can be saved by using automated lights that turn off when there is a lack of movement or where there is enough ambient light.
The controlled variable of this system would be the level of light given off by the light bulb. This variable is manipulated by the change in energy supplied to the bulb. The operating range would be determined by the level of light detected by the light sensor. The system would operate off of two main ranges of operation. The “good” range of operation would be the range in which there is enough natural light, such as during the daytime or when nearby lights are illuminated enough. In this case, a signal would be sent by the sensor to turn off the bulb. The system would turn on upon reaching the “bad” range of operation, in which not enough natural light is present for proper sight. A signal would be sent by the sensor to the controller, causing the bulb to apply light.
While the dimming and motion activating functions are the cornerstones of the system, they would not be necessary to act in the bare-bones functions of a conventional light. Fortunately, in the event of a malfunction, not all functionality would be lost. Therefore, the product would still function as a light without the necessary adjustment of light level. The light level sensor control is an improvement because it saves energy on lights when the energy applied is not necessary. During daylight, it is more efficient for the light to be off. The motion sensor control is an improvement because it makes living alone more manageable. If a person came home from grocery shopping late at night, the automated light sensors would turn on at his porch and in his house as soon as he is within a certain distance.
The motion sensor is another benefit to the operation of the light function. It is supportive of the user experience due to the convenience of an automatic versus manual control. If there is no error reading in the light sensor, the motion sensor does not respond to motion because there is already enough light present. Motion control creates a safer environment such as in parking lots or along sidewalks among other public places. Furthermore, this product is cost effective, since less power is used up by the light bulb than if the lights were on for the whole day.
The manipulated variable is the energy applied, which can have numerous points of manipulation, such as for a daytime and nighttime setting. Once the surroundings reach a certain level of brightness without movement, the system can shut off completely. For examples, after 5 minutes of inactivity or sufficient lights for 5 minutes. At this point, there would be no electricity applied to the light bulb, but there would still be electricity flowing through the sensor so that it could allow for a quick response through the controller. During a lack of motion, energy would be saved due to the light bulb being off.
Because of the presence of two sensors, potential disturbances in either sensor could affect the output. Light level disturbances may include the headlights of nearby cars or lights from television or computer screens. Motion disturbances, like the small movements of bugs flying around the sensor could also have effects. In addition, the sensor would need to ignore the effects of inclement weather, such as rain or snow.
To mitigate these disturbances, a PI controller should be used. A derivative response would be too erratic for the potentially noisy data received by the sensors. The infrared motion sensor, designed to detect high levels of infrared radiation, could be set to only send a signal for detected heat sources of greater than 90°F. Requiring these sources to be localized would avoid issues arising from a summer day when it is above 90°F outside.
Figure 1: Infrared Motion Sensor
The variables of light level and motion disturbances would both be controlled by the manipulation of energy. A sudden detection of motion would require a quick response of energy from the controller while a sudden change in light would require a slow or delayed response. As a person approaches a motion sensor controlled light in a parking garage, it is important that the light illuminate. A slow response in this case would not do much for safety. On the other hand, light disturbances from passing headlights do not need to be addressed by this light system. Changes in light level typically happen over a long time, so a slow response would be acceptable.
The process would be controlled via a third order feedback loop while the motion sensor would contribute a simple unit step to the controller. The following block diagram represents the light and motion sensor system. Xdl and Xdm represent the light and motion disturbances respectively. Gdl and Gdm represent the transfer function of the light and motion disturbances. Xspl and Xspm represent the set points for light and motion. With this block diagram, the system would be developed and the product would be possible. No more useless energy consumption!
Figure 2: Block Diagram
Reference:
- http://www.safewise.com/resources/motion-sensor-guide
The artificial light source that is controlled by both motion and light sensors would be extremely useful to the general public. It could be implemented in places ranging from personal households to public buildings to street corners and parking lots. It would be great to see this technology implemented locally at Lafayette in college academic buildings such as Hugel which keeps most of its lights on full time even when it is unoccupied at night and in college dorm hallways which also unnecessarily keep all there hallway lights at max brightness during the nighttime hours.
Manipulating the amount of electricity allowed to a light source does seem like the most logical variable to manipulate when trying to control the light output. This is since the flow of electricity can be used to control both the motion sensing case and the light dimming case. Although many of the potential disturbance variables were mentioned in the article, one disturbance that was not fully discussed is when light is blocked from reaching the light sensor. This could simply take the form of clouds blocking the light from the sun or the blinds on a window being closed. In both of these cases, a controller can easily correct for the changes in light. Conversely, this could also take the form of a shadow or a particle of dust blocking the path of light to the sensor. This would be increasingly more difficult to correct in cases where there is already an ideal amount of light in a room, since the amount of light being observed by the sensor will not be the same amount of light which is actually present in the room. One of the disturbance variables for the motion activated feature that was not fully discussed was temperature. A person who walks into a building from being outside on an extremely cold day may not have the capability to emit enough thermal energy to be detected by the proposed infrared motion sensor and may not be able trigger the lights into turning on.
This system should ideally be set up as a feedback loop so that the sensors can monitor the total light in a room and react accordingly by changing the amount of electricity supplied to the light source. I agree that a PI controller is the most logical option to correct both for the disturbances and for changes in the set amount of light desired in a room. Unlike a proportional controller, a PI controller does not result in an offset and would be able to accurately return to the set point. As the article mentions, adding a derivative component would result in the control doing a poor job accounting for the noise from slight external light fluctuations. The controller parameters can be optimized by using the closed loop tuning method since it will be relatively simple to see a sustained oscillation in the output amount of light. Because the process only involves the amount of electricity supplied to a light source, there is little risk if the oscillations become divergent when trying to tune the controller with the closed loop method.
Lights controlled by motion as well as external sources of light are practical, as they are currently used in many different situations. They are also a good source of inspiration about how controls are used in the real world because there is definitely a lot of applicability for these lights both for general use as well as in more specialized situations. I can see people installing such a device throughout their home not only to save energy, but simply for the sake of convenience. The way it is presented here makes it seem a little like it is a brand new idea, which it is not, but it is an interesting situation to analyze none the less.
The set-up of the variables is presented in a fairly straightforward manner, and ample discussion of each type of variable is included. It makes sense, based on the type of system being described, that there is only one controlled variable and one manipulated variable, but multiple disturbance variables. It is convenient for the system that their manipulated variable is electrical current, because that is fairly easy to control. What presents as a challenge to the system is that there are so many different manifestations of disturbance variables, but they do a good job highlighting possible disruptions in their system by exploring both light and motion related effects.
I agree with the type of control they have proposed for the system. A derivative controller would most likely be too sensitive to variance in input to the sensors, and so would not be an effective component to the controller. Having both proportional and integral control will allow the system to utilize the information that it is being given as well as that which it has previously gained. In this fashion, one could potentially input date and time information if the lights were outside or in a room with a lot of windows, so the system could have a basis in case of sensor failure and to prevent a drift from the normal range of operation (defined by the authors as the “good” and “bad” ranges). Their concern about ambient temperature could be resolved more succinctly than having a proximity requirement by including a temperature sensor to give the controller more information about the surroundings so it is better able to recognize a disturbance in them that would cause the light(s) to come on or go off. It may be most efficient for tuning the system if a test environment is selected for the initial design so the various types of disturbance can be carefully considered, but also minimized.
An application that automatically dims and shuts lights on and off is definitely practical. As these lights already exist in many buildings, I think there is certainly a market for this product. This product could be useful here at Lafayette, and as mentioned in the article, could help reduce energy bills and be a more sustainable energy option.
The control variables of amount of outside light and motion make sense. The definition of the parameters for “good” and bad” are a little fuzzy. It makes sense that the amount of light emitted by the light bulb is dependent on the amount of light outside. What confuses me, however, is how can someone adjust the amount of light being emitted based on the amount of light outside (i.e. if someone tends to like the room to be brighter than another person). It makes sense to make the manipulated variable the amount of energy sent to the light bulb since that is what is most easily controlled. There are a wide range of deviation variables since there will be so much noisy data sent to the system. The deviation variables mentioned in this article all make sense, except for the exclusion of inclement weather. Unless I am misunderstanding what the article is saying, it would make sense to me to take the weather into account since it tends to get darker when it snows or rains.
I agree with the PI controller proposed by the authors of this article. The data received by the controller will likely be very noisy, as there will most likely be periods of increased movement and outside light variation. Having both the proportional controller and integral controller would make sense to minimize the instability of the signal, but also to be able to react to the continuous signal received. I also agree that the system is set up as a feedback loop. This set-up allows for the sensors to receive information and then change the light output accordingly by changing the amount of energy supplied to the light. This is easiest because it would not logically make sense to try to automate a process, but then use a feedforward loop that does not account for changes in the controlled variable. To better tune or control the parameters, there could be a piece put in that is selective for different environments and light settings (i.e. someone who likes more light rather than less light). This would allow further automation and personalization of the system.
In this day and age, it appears that the newest trend in architecture is the design of “green buildings”. All over the United States, cities are developing skyscrapers that can run on as little energy as possible. One technique that is often implemented by the design team is to add as much natural light as possible by the addition of windows or glass walls. This has proven to be very effective at reducing energy consumption within modern buildings. However, it has also caused buildings to have wildly inconsistent lighting throughout the day. As the angle of the sun changes, these windows allow different amounts of light. Controlling the lighting in a room could alleviate this problem.
In the same fashion, my dad was always yelling at me when I was little to make sure I turned off the lights when I left the room. Not doing so was unnecessarily consuming energy and driving up our electric bill. Adding motion sensors to eliminate wasteful consumption could also drastically improve the energy efficiency of lighting systems.
This group effectively identified their control variable to be light intensity and they also found their manipulated variable to be the energy supplied to the light bulb. When the light intensity is measured a controller decides whether to send more or less energy to the bulb. If the controller sends less energy the intensity of the bulb (and therefore the surrounding area) decreases. The reverse is also true. More energy to the bulb will yield a higher light intensity.
The controller used by this group is the exact controller I would have used. The changes in natural light occur very slowly over the course of a day. Therefore, derivative control, which responds well to fast changes, would be unnecessary. However, a proportional control alone will never reach the set point so it is important to have integral control as well. Overall, a PI controller should be used.
As the world shifts to become a more environmentally sustainable place, inventions like this are needed. This product could reduce wastefulness through a motion sensor while also providing consistent lighting through a light sensor. I can see this product being used in the construction of “green” skyscrapers that are popping up all over the country and world. Since installation could be a little tricky for your “average Joe” I think you should focus on new instillations instead of lighting upgrades. Maybe you could target the sale of your product to construction companies and electricians. Hopefully in the future all lights could have this additional control.