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City Streetlights Become Smart: The New LED Street Lamps, Part 3

In part 2 of this blog series I described a new solution for the illumination of the streets in big cities by the company STMicroelectronics.

Furthermore, there are many companies like Marvell, Dialog, and Infineon that are working on an LED driving project for ICs and commonly the PWM (pulse width modulation) solution is utilized to deliver the required stable power to an LED row that is utilized for many common consumer applications, for example to illuminate the displays of smartphones or tablets.

Such an IC that provides very stable electric power required by the LED is constituted basically of switching voltage regulators that are able to manage the power coming from a DC source, typically a lithium battery, by guaranteeing good conversion efficiency, i.e., the ratio between the output power and the input power of the voltage regulator which feeds the LED.

The basic mechanism of the power conversion of the switching power regulator is the PWM strategy: An integrated power switch is turned on and off for a fixed time interval, during a period of switching, the resulting pulsed waveform is filtered by a capacitor filter at the output, to provide a constant DC voltage and current to the LED array (see Figure1):

Figure 1

The basic operating mode of the step up configuration of an integrated voltage DC-DC to supply a constant power to a LED array.

The basic operating mode of the step up configuration of an integrated voltage DC-DC to supply a constant power to a LED array.

The ST new smart solution is very interesting to me because it improves the LED driver by means of the action of the microprocessor that is the key core of the smart light system.

The microprocessor can regulate the brightness of the light emitted by the LED by using the feedback signal of a light sensor integrated in the smart packaged system. The microprocessor puts intelligence into the management of the light emitted by the LED and makes it possible for smart energy saving for street illumination purposes. This new solution holds a great deal of potential because of the high number of possible functionalities that can be added to the microcontroller.

The management of the energy supplied to the street lights for the illumination of cities usually does not take into account environmental conditions, in which the lights have to operate regardless of the material constituting the lamps, but something is changing. From an ST press release:

Many cities around the world have started to convert their existing streetlamps to use LED technology and even more are drawing up plans to do so. In the USA, for example, Boston, Massachusetts had converted 40% of its 64,000 electric streetlamps to LEDs by the end of 2012 and was already realizing $2.8 million savings annually in electricity cost, about 35% of that expense.

The city of San Jose, Calif., has agreed to this project (see Figure 2): “At the AlwaysOn GoingGreen conference in Sausalito, Calif., San Jose Mayor Chuck Reed discusses a plan to update the city's 62,000 street lights with motion sensor controls, networking technologies, and LED bulbs.”

Figure 2

The Smart Street LED lights project implemented in San Jose, Calif.

The Smart Street LED lights project implemented in San Jose, Calif.

Do you think this solution will impact the environment of the cities less than the present solution? Do you prefer LED lights for their low power consumption and the simple driving circuitry?

26 comments on “City Streetlights Become Smart: The New LED Street Lamps, Part 3

  1. etnapowers
    June 16, 2014

    The PWM solution is very effective to filter the pulses at the switching node. The filtering operation results in a very stable DC output voltage to feed the load. The key point of this system is the controller of the power switch: it has to guarantee a effective transfer of the energy from the input voltage source to the output load and not vice versa. Some transition times guard bands are required.

  2. etnapowers
    June 16, 2014

    The microcontroller action has high potential of piloting the LED streetlights in a really smart way, based on the feedback signal of a photodiode. The presence of the microcontroller allows another option: an RF module for a remote control of the streetlights, by mean of the Internet of Things technology.

  3. Davidled
    June 16, 2014

    I am wondering what type feedback signal of photodiode would be sent to microcontroller and photodiode's signal could be used in any type power LED. I think that there is a different feature between LED driver with microcontroller and LED driver without it. 

  4. Davidled
    June 16, 2014

    PWM technique would be used for dimming LED, as modulating the input voltage. Timer could be added to turn the street LED on or off for a certain period time. I guess that PWM with timer feature could be a good combination for the street LED.

  5. etnapowers
    June 17, 2014

    @DaeJ: basically the photodiode is reverse biased and the current generated by the photons is sensed in a resistor, that is connected in parallel to the diode.

  6. samicksha
    June 17, 2014

    curious to learn more about the code execution, the microcontroller must not only time which causes the pulse generation, but also run the code which controls the LED output.

  7. goafrit2
    June 22, 2014

    >> The presence of the microcontroller allows another option: an RF module for a remote control of the streetlights, by mean of the Internet of Things technology.

    We are going into a new level in this. One firm Electric Imp provides a great tool that helps not just to improve the “smartness” in these systems but also integrate them into Internet of Things. That way they become an extension of the web and can be controlled more efficiently.

  8. goafrit2
    June 22, 2014

    >>  I guess that PWM with timer feature could be a good combination for the street LED.

    Do you think modulating the signal could increase the energy requirement in these lights? In other words, a DC signal does not dissipate a lot of power compared to a constantly varying signal.

  9. fasmicro
    June 22, 2014

     basically the photodiode is reverse biased and the current generated by the photons is sensed in a resistor, that is connected in parallel to the diode.

    You are correct – the resistor is called  SENSE resistor which through the current flowing it to give vollage which is used in the loop. The strength of that current, sensed by the resistor, is used to control. It is a standard technique used in most designs.

  10. fasmicro
    June 22, 2014

    Yes, but most times the MCU is very faster than the loop. So, it has all the time to complete the operation before the next sample is available. The code will not be that complex since the sequence is direct.

  11. Davidled
    June 22, 2014

    I think that your comment illustrated power consumption comparison between DC and AC. Power source could be depending on LED lighting electric requirement. Timer indicated that lighting in the street could be turned on or off automatically from control box in the city office. Therefore the optimum scheduling method would save the energy in the city lighting.

  12. chirshadblog
    June 23, 2014

    @Daej: I think power consumption plays a major role since it has a direct impact with the running cost on a monthly basis. It's a running investment so needs to be considered quite closely. 

  13. chirshadblog
    June 23, 2014

    @fasmicro: Indeed it's a good move to have standardized things. Then things will be easy to monitor once in the debugging mode. 

  14. chirshadblog
    June 23, 2014

    @goafrit2: Yes it will definitely. 

  15. chirshadblog
    June 23, 2014

    @goafrit2: So will the controllability be easy ? 

  16. etnapowers
    June 23, 2014

    Agreed, the IOT technology is really suitable with the street lights LED applications, it's the next frontier of lighting smart management, both for homes and city lights.

  17. chirshadblog
    June 24, 2014

    @etnapowers: Yes indeed that will be the next big thing in the lighting industry. I think LED lights will replace all

  18. RedDerek
    June 26, 2014

    Though it adds a bit more cost…

    One added feature would be a dim-mode and a bright mode of operation. The streetlamp can continually look downwards at the illuminated area and then would brighten up the lamp as a person walks into the area. Thus the lamp can operate at a low illumination level to save power, but still provide some light. Then brighten up to allow the pedistrian a better view.

    Heck, you can use a small rf communication between lamps, in a small region, that could actually brighten up other nearby lamps, if not along the route.

    (just getting a bit crazy on the thought process)

  19. goafrit2
    July 1, 2014

    Timer indicated that lighting in the street could be turned on or off automatically from control box in the city office. Therefore the optimum scheduling method would save the energy in the city lighting.

    Besides technology, control and scheduling management offer a great deal in keeping lighting cost down. Even in homes, we know how to schedule our heaters during winter to get the best value in heating at lowest possible electricity bill. That can be done in cities if they use technology to improve sensing and automation.

  20. goafrit2
    July 1, 2014

    I think power consumption plays a major role since it has a direct impact with the running cost on a monthly basis.

    That is one element of the cost model. But also understand that we waste energy by not scheduling lighting well. A complete nexus of all options will be necessary to manage cost. Compared with power consumption/loss power, scheduling management could be more strategic.

  21. goafrit2
    July 1, 2014

    Indeed it's a good move to have standardized things. Then things will be easy to monitor once in the debugging mode. 

    Unfortunately in some new industries, standards are not robust. Increasingly I see lesser cooperations in getting these issues of standards done. Everyone wants to kick the other out of business.

  22. goafrit2
    July 1, 2014

    So will the controllability be easy ? 

    Absolutely. When you have a top-tier engineering team, you can execute any strategy. You need to see this from the software angle over pure hardware.

  23. goafrit2
    July 1, 2014

    Agreed, the IOT technology is really suitable with the street lights LED applications, it's the next frontier of lighting smart management, both for homes and city lights.

    It is already part of the equation. Electric Imp has developed great products that can help any city improve its capability to monitor lighting and also save costs. They are implemeting storage within electronics with added IP for IoT.

  24. goafrit2
    July 1, 2014

    @RedDerek, it may not add cost that much if the strategy follows electronics where the benefits of Moore's law comes into place. Electronics are adding marginal costs especially when they are integrated ones. I guess any good product will follow that route thereby ensuring that cost will not be that high.

  25. fasmicro
    July 3, 2014

    >> Timer indicated that lighting in the street could be turned on or off automatically from control box in the city office.

    I will prefer a sensor in the vicinity of the street light so that it can turn on and off depending on the ambient sunlight. There is no need of hiring someone to do that from the office.

  26. fasmicro
    July 3, 2014

    Companies like Phillip are investing heavily hoping they will become category kings in the LED industry. In the next 7 -10 years, LED will become the defacto lighting bulb of choice and all non-LED light bulbs will disappear.

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