> Quick answer: The dusk-to-dawn sensor triggers the LED driver when ambient light drops below 400 lux, initiating a gradual current scaling based on battery charge and voltage to avoid power surges [1][12].
Solar lamps play an essential role in Romania’s rural and urban environments, providing reliable nighttime illumination powered by renewable energy. The precise interaction between the dusk-to-dawn sensor and the LED driver ensures that solar lamps transition smoothly to a 2000-lumen output without causing a battery power surge. This article explores how this transition is managed through integrated sensing and dynamic current control.
How Dusk-to-Dawn Sensors Initiate the Transition
The dusk-to-dawn sensor, typically an optical sensor such as a photodiode or LDR, detects ambient light intensity drops at sunset [3][19]. When ambient light falls below 400 lux, the solar panel’s output voltage decreases, triggering the LED driver to activate [12][21]. This mechanism ensures that the system only activates when sufficient darkness has occurred, preventing premature or false triggering.
Dynamic Energy Management Strategy
Once activated, the LED driver does not immediately deliver full power. Instead, it operates under a dynamic energy management strategy that scales the output based on available battery charge and voltage levels [1][14]. The system uses an energy scaler circuit to adjust the current supplied to the LEDs according to remaining battery energy, ensuring consistent LED output over time while preserving battery life.
Maintaining Constant Current Delivery
The driver circuit maintains a constant current level—typically capped at 20–25 mA per LED—to prevent overdriving and premature failure [1][14]. This is achieved by adjusting the voltage output signal in response to the energy scaler circuit, maintaining stable current delivery across fluctuating input voltages [17].
Preventing Power Surges
A critical feature that prevents power surges is the driver’s ability to shut down LEDs when battery voltage falls below 2.8 VDC, conserving residual energy and preventing deep discharge [1][14]. Protective features such as short-circuit protection and overvoltage safeguards are also included for reliability in outdoor environments [7].
System Complexity and Design Insights
The solar panel itself can serve as the primary light sensor, eliminating the need for a separate photocell. This dual-purpose design reduces component count and cost while maintaining reliable operation [15][12]. The integration of sensing and energy harvesting enhances system simplicity and reliability.
Key Takeaways
- Dusk-to-dawn sensors trigger LED drivers when ambient light drops to 400 lux.
- Dynamic current scaling ensures consistent brightness without battery surges.
- Constant current delivery prevents overdriving and premature failure.
- Solar panels serve as integrated light sensors, reducing component complexity.
- Protective features such as cutoffs at low voltage prevent power surges.
Frequently Asked Questions
[
{„q”: „How does the dusk-to-dawn sensor work in solar lamps?”, „a”: „The sensor detects ambient light drops below 400 lux and triggers the LED driver [12][21].”},
{„q”: „What prevents sudden power surges when transitioning to full brightness?”, „a”: „Dynamic current scaling adjusts output based on battery charge, avoiding surges [1][14].”},
{„q”: „Can solar panels also serve as light sensors in these systems?”, „a”: „Yes, they can integrate sensing and energy harvesting, reducing component count [15][12].”}
]
References
- [1] US20110252678A1_-_Method_apparatus_and_system_-_Google_Patents__66ffc305 — patent
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for driving the LEDs at the correct level of current consumption during all the night time hours. – the exemplary circuit of FIG. 14 can evenly divide the night time hours required for LED operation and scale the output signal to match with the available battery energy that has previously been stored during the daytime hours and provided to the scaler divider circuit in the form of the analog charge level input signal provided from the circuit of FIG. 12 . – FIG. 15 is the exemplary LED driver circuit, which adjusts the voltage output signal from the energy scaler circuit so that none of the LEDs operate at more than approximately 20 mA or alternatively 25 mA per LED, which could overdrive the LEDs and cause early failure. All during the night time hours, the LED driver circuit continues to provide battery power to operate the LEDs at a constant level of current consumption. The LEDs are connected to the LED driver circuit through jumpers J 10 and J 11 located at the lower right hand corner of FIG. 15 . If the battery voltage decreases down to 3.0 VDC due to power consumption by the LEDs, then the LED driver circuit turns down the current consumption by the LEDs regardless the input from the scaler energy circuit to extend the LED operating time. If the battery voltage continues to decrease down to below about 2.8 VDC, the transistor Q 2 turns off the LEDs to conserve some of the battery energy and avoid over-discharging the battery. – FIG. 16 further illustrates the battery
- [3] US20170055324A1_-_Apparatus_retrofit_kit_and_-_Google_Patents__f5522dda — patent
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mains power source or network) via wires or cables 215 (e.g., overhead, underground). The luminaire 202 may include one or more electronic ballasts ordrivers 234, for instance where a ballast is needed or useful for the particular type of illumination or light source(s) 204. The ballast(s) or driver(s) 234 condition the supply, line or mains power to provide proper starting and operating electrical conditions (e.g., current, voltage, limiting in-rush current) for the particular illumination or light source(s) 204. The ballast(s) or driver(s) 234 may be an integral or unitary part of the light source(s) 204, or may be a separate discrete component therefrom. The ballast(s) or driver(s) 234 can include a power supply, rectifying AC power and stepping down a voltage of the electrical power supplied from theexternal power source 213. – A legacy luminaire 202 may optionally include dusk-to-dawn and/or motion sensing control mechanism orcircuitry 216 and one or moreoptical sensors 218. Theoptical sensor 218 can take any of a variety of forms, including light sensitive or light responsive photosensors, cadmium sulfide cells, photodiodes, phototransistors, ambient light sensor integrated circuits currently commercially available. Thecontrol circuitry 216 may be an analog circuit, digital circuit or may include both analog and digital circuit components. Again, a conventional commercially available luminaire with an integral control mechanism may be employed. – In the legacy luminaire
- [7] CN107809825A_-_Photovoltaic_controller_and_brightness__b6791ba7 — patent
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LED has many-side in the factor that the application of solar lighting field is restricted：First, the sun Can light fixture rainy days when because generated energy is few, the problem of not working often occurs in light fixture or lighting time is short；2nd, electricity is adapted to Narrow range is pressed, in solar energy lamp system, nominal voltage is generally two kinds of DC12V and DC24V, solar LED control on the market Device processed is mostly directed to a kind of voltage therein, voltage adaptation narrow range；3rd, LED light source power is unadjustable, due to circuit design Problem, many drivers do not possess dimming function, cause LED light source to always work in full power state；4th, defencive function Difference, driver do not possess the functions such as reversal connection, output short-circuit, overvoltage protection, and poor reliability during use, circuit is easy to damage；5th, High temperature has a strong impact on to LED light source service life, when great power LED works under rated current state, can produce heat, LED If junction temperature can not control in safe range, it will accelerate its light decay, shorten LED service life. At present, in order to reduce the operating temperature of LED light source, the fado that does conventional at present is using reduction LED drive circuit Operating current, its shortcoming are that power supply power supplying efficiency is low, can not give full play to LED light source efficiently, the ch
- [12] US7794103B2_-_Parking_space_barrier_block_with_-_Google_Patents__6df2a4d9 — patent
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to a safe value by resistor R 2 . – the component values of R 1 and D 7 are coordinated to produce Q 1 turn-ON when the intensity of incident skylight, indicated by arrows 31 in FIG. 9 , rises above a predetermined intensity level. – Q 1 will turn ON and Q 2 will turn OFF (LEDs OFF). – Q 1 will turn OFF and Q 2 will turn ON (LEDs ON) at sunset on a clear day (for example at location latitude +32.85 N, longitude ⁇ 96.48 W). – the collector output terminal 32 of transistor switch Q 1 is connected to the gate input node 33 of the LED power driver transistor Q 2 . – the gate input node 33 formed between resistor R 2 and clamping diode D 8 , applies the clamping voltage of Zener diode D 8 as a bias voltage to the base of the driver power transistor Q 2 when Q 1 is OFF. – the clamping diode D 8 is a Zener diode whose clamping voltage is selected with due consideration of the operating voltage drop across the LED lamps and their current limiting resistors, which typically is a total of about 8 VDC for the LED components identified in Table 1. – the power driver transistor Q 2 requires a base-emitter bias of about +1 VDC to turn ON in saturation switching mode. Accordingly, the clamping diode D 8 , which is rated at a clamping voltage of 9.1 VDC, produces a differential turn-on bias (about 1.1 VDC) across the base-emitter junction of Q 2 when Q 1 is OFF. – Operating power is disconnected from the LED lamps when Q 2 turns OFF. This enables the current output of the solar panel PV 1 an
- [14] US20110252678A1_-_Method_apparatus_and_system_-_Google_Patents__66ffc305 — patent
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correct level of current consumption during all the night time hours. The exemplary circuit ofFIG. 14 can evenly divide the night time hours required for LED operation and scale the output signal to match with the available battery energy that has previously been stored during the daytime hours and provided to the scaler divider circuit in the form of the analog charge level input signal provided from the circuit ofFIG. 12 . – FIG. 15 is the exemplary LED driver circuit, which adjusts the voltage output signal from the energy scaler circuit so that none of the LEDs operate at more than approximately 20 mA or alternatively 25 mA per LED, which could overdrive the LEDs and cause early failure. All during the night time hours, the LED driver circuit continues to provide battery power to operate the LEDs at a constant level of current consumption. The LEDs are connected to the LED driver circuit through jumpers J10 and J11 located at the lower right hand corner ofFIG. 15 . If the battery voltage decreases down to 3.0 VDC due to power consumption by the LEDs, then the LED driver circuit turns down the current consumption by the LEDs regardless the input from the scaler energy circuit to extend the LED operating time. If the battery voltage continues to decrease down to below about 2.8 VDC, the transistor Q2 turns off the LEDs to conserve some of the battery energy and avoid over-discharging the battery. – FIG. 16 further illustrates the battery protection features of the control c
- [15] PREMA_Semiconductor_Releases_New_Boost_LED_Driver_For_Solar__8fb35011 — authority
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# PREMA Semiconductor Releases New Boost LED Driver For Solar Lamps – New Products Source: Blog/Web URL: https://eepower.com/new-industry-products/prema-semiconductor-releases-new-boost-led-driver-for-solar-lamps/ Author: Jeff Shepard Date: 2007-12-10 PREMA Semiconductor Releases New Boost LED Driver For Solar Lamps PREMA Semiconductor GmbH has extended its family of LED drivers with a boost driver for solar applications. The new PR4403 drives and controls white LEDs out of one single battery charged by solar cells. It uses the connected solar cells to detect daylight. LED solar lamps operate with automatic LED control depending on the ambient light level. The battery is charged by solar cells. According to the company, this normally requires several components like Schottky diodes, capacitors, resistors, two or three rechargeable battery cells and a photo resistor. In contrast to this standard solution the PR4403 saves several components, as it is able to drive the current for the white LED out of a single rechargeable battery cell. The expensive photo resistor is also claimed to be no longer needed. A supply voltage of down to 0.9V is sufficient for the IC to drive a current of up to 40mA independent of the input voltage. The value of the external inductor defines the LED current. Instead of the photo resistor, the solar cell is directly connected to the IC for daylight level detection, and an optional resistor sets the light threshold. Depending on the voltage at this conn
- [17] US9992826B1_-_Dual_mode_constant_current_LED_driver__71bc120a — patent
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the output voltage of the driver using a DC voltage signal provided by the DC power source, a current flowing through the first inductor, a switching frequency of the first switch, and a duty ratio of the first switch. – the device may further include an electro-magnetic interference (EMI) filter operatively connected between the DC power source and the converter, and configured to eliminate high frequency components of a DC voltage signal from the DC power source. – EMI electro-magnetic interference Landscapes – Circuit Arrangement For Electric Light Sources In General (AREA) Abstract A dual mode constant output current LED driver is capable of operating with a very wide range of input direct current (DC) voltage. This provides an effective topology for a wide range of constant output current LED drivers, and allows for changing the number of connected LEDs without negatively impacting the output current. The LED driver includes a converter and a mode selection circuit that control the modes of the circuit based on the voltage. The converter and mode selection circuit operate in a buck-boost mode when the output voltage of the LED driver is less than the DC input voltage plus a first threshold amount, and in a boost mode when the output voltage of the LED driver is greater than the DC input voltage plus a second threshold amount. Description The present disclosure relates to power supplies suitable for driving light emitting diode (LED) lighting systems as well as other elec
- [19] US20170055324A1_-_Apparatus_retrofit_kit_and_-_Google_Patents__f5522dda — patent
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the electrical power supplied from the external power source 213 . – a legacy luminaire 202 may optionally include dusk-to-dawn and/or motion sensing control mechanism or circuitry 216 and one or more optical sensors 218 . – the optical sensor 218 can take any of a variety of forms, including light sensitive or light responsive photosensors, cadmium sulfide cells, photodiodes, phototransistors, ambient light sensor integrated circuits currently commercially available. – the control circuitry 216 may be an analog circuit, digital circuit or may include both analog and digital circuit components. Again, a conventional commercially available luminaire with an integral control mechanism may be employed. – the dusk-to-dawn and/or motion sensing control mechanism or circuitry 216 can implement both dusk-to-dawn, and optionally motion or proximity based control. – the control mechanism or circuitry 216 relies on signals from the optical sensor 218 to implement motion or proximity sensing only during a period after a level of light or illumination in the environment has fallen below a turn ON threshold (e.g., 10 Lux) and before the level of illuminations exceeds a turn OFF threshold (e.g., 30 Lux). – the control mechanism will turn the light source(s) 204 ON for a period of time in response to the detection of motion between dusk and dawn, turning the light source(s) 204 OFF after the period of time. – the turn ON and turn OFF thresholds could be equivalent, such would likely produce
- [21] US7794103B2_-_Parking_space_barrier_block_with_-_Google_Patents__6df2a4d9 — patent
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D4. The collector output terminal 32 of the switching transistor Q1 is connected to the signal input node 33 of the driver power control circuit 28. In the absence of sufficient ambient lighting, the output of the solar panel 22 does not provide enough driving current to develop a bias voltage that exceeds the turn-on threshold of transistor Q1. Consequently, under defined low-level ambient skylight intensity conditions (for example, less than 400 lux), Q1 is non-conducting (OFF), and a bias voltage develops across the power driver input node 33 as current flows through the Zener diode D8. The bias voltage is clamped at a turn-on voltage level by Zener diode D8, rendering Q2 conducting (ON), and applying operating power to the LED lamp group 64 (white light illumination) and LED lamp group 66 (yellow light illumination). When ambient skylight intensity rises above the defined threshold value, Q1 turns ON, pulling the input node 33 and base of Q2 to near zero reference potential. Resistor R2, which provides bias current to Q2, has a resistance value of 10 K ohms and is connected in series with the collector of Q1 through the input node 33, thereby safely limiting the current flowing through the collector and grounded emitter of Q1 to less than 1.5 mA under maximum photovoltaic supply conditions. Consequently, Q2 is rendered non-conducting (OFF), thus removing operating power from both LED groups during daylight operation. The electronic control circuits 26 and 28 ensure that a
for driving the LEDs at the correct level of current consumption during all the night time hours. – the exemplary circuit of FIG. 14 can evenly divide the night time hours required for LED operation and scale the output signal to match with the available battery energy that has previously been stored during the daytime hours and provided to the scaler divider circuit in the form of the analog charge level input signal provided from the circuit of FIG. 12 . – FIG. 15 is the exemplary LED driver circuit, which adjusts the voltage output signal from the energy scaler circuit so that none of the LEDs operate at more than approximately 20 mA or alternatively 25 mA per LED, which could overdrive the LEDs and cause early failure. All during the night time hours, the LED driver circuit continues to provide battery power to operate the LEDs at a constant level of current consumption. The LEDs are connected to the LED driver circuit through jumpers J 10 and J 11 located at the lower right hand corner of FIG. 15 . If the battery voltage decreases down to 3.0 VDC due to power consumption by the LEDs, then the LED driver circuit turns down the current consumption by the LEDs regardless the input from the scaler energy circuit to extend the LED operating time. If the battery voltage continues to decrease down to below about 2.8 VDC, the transistor Q 2 turns off the LEDs to conserve some of the battery energy and avoid over-discharging the battery. – FIG. 16 further illustrates the battery
mains power source or network) via wires or cables 215 (e.g., overhead, underground). The luminaire 202 may include one or more electronic ballasts ordrivers 234, for instance where a ballast is needed or useful for the particular type of illumination or light source(s) 204. The ballast(s) or driver(s) 234 condition the supply, line or mains power to provide proper starting and operating electrical conditions (e.g., current, voltage, limiting in-rush current) for the particular illumination or light source(s) 204. The ballast(s) or driver(s) 234 may be an integral or unitary part of the light source(s) 204, or may be a separate discrete component therefrom. The ballast(s) or driver(s) 234 can include a power supply, rectifying AC power and stepping down a voltage of the electrical power supplied from theexternal power source 213. – A legacy luminaire 202 may optionally include dusk-to-dawn and/or motion sensing control mechanism orcircuitry 216 and one or moreoptical sensors 218. Theoptical sensor 218 can take any of a variety of forms, including light sensitive or light responsive photosensors, cadmium sulfide cells, photodiodes, phototransistors, ambient light sensor integrated circuits currently commercially available. Thecontrol circuitry 216 may be an analog circuit, digital circuit or may include both analog and digital circuit components. Again, a conventional commercially available luminaire with an integral control mechanism may be employed. – In the legacy luminaire
LED has many-side in the factor that the application of solar lighting field is restricted：First, the sun Can light fixture rainy days when because generated energy is few, the problem of not working often occurs in light fixture or lighting time is short；2nd, electricity is adapted to Narrow range is pressed, in solar energy lamp system, nominal voltage is generally two kinds of DC12V and DC24V, solar LED control on the market Device processed is mostly directed to a kind of voltage therein, voltage adaptation narrow range；3rd, LED light source power is unadjustable, due to circuit design Problem, many drivers do not possess dimming function, cause LED light source to always work in full power state；4th, defencive function Difference, driver do not possess the functions such as reversal connection, output short-circuit, overvoltage protection, and poor reliability during use, circuit is easy to damage；5th, High temperature has a strong impact on to LED light source service life, when great power LED works under rated current state, can produce heat, LED If junction temperature can not control in safe range, it will accelerate its light decay, shorten LED service life. At present, in order to reduce the operating temperature of LED light source, the fado that does conventional at present is using reduction LED drive circuit Operating current, its shortcoming are that power supply power supplying efficiency is low, can not give full play to LED light source efficiently, the ch
to a safe value by resistor R 2 . – the component values of R 1 and D 7 are coordinated to produce Q 1 turn-ON when the intensity of incident skylight, indicated by arrows 31 in FIG. 9 , rises above a predetermined intensity level. – Q 1 will turn ON and Q 2 will turn OFF (LEDs OFF). – Q 1 will turn OFF and Q 2 will turn ON (LEDs ON) at sunset on a clear day (for example at location latitude +32.85 N, longitude ⁇ 96.48 W). – the collector output terminal 32 of transistor switch Q 1 is connected to the gate input node 33 of the LED power driver transistor Q 2 . – the gate input node 33 formed between resistor R 2 and clamping diode D 8 , applies the clamping voltage of Zener diode D 8 as a bias voltage to the base of the driver power transistor Q 2 when Q 1 is OFF. – the clamping diode D 8 is a Zener diode whose clamping voltage is selected with due consideration of the operating voltage drop across the LED lamps and their current limiting resistors, which typically is a total of about 8 VDC for the LED components identified in Table 1. – the power driver transistor Q 2 requires a base-emitter bias of about +1 VDC to turn ON in saturation switching mode. Accordingly, the clamping diode D 8 , which is rated at a clamping voltage of 9.1 VDC, produces a differential turn-on bias (about 1.1 VDC) across the base-emitter junction of Q 2 when Q 1 is OFF. – Operating power is disconnected from the LED lamps when Q 2 turns OFF. This enables the current output of the solar panel PV 1 an
correct level of current consumption during all the night time hours. The exemplary circuit ofFIG. 14 can evenly divide the night time hours required for LED operation and scale the output signal to match with the available battery energy that has previously been stored during the daytime hours and provided to the scaler divider circuit in the form of the analog charge level input signal provided from the circuit ofFIG. 12 . – FIG. 15 is the exemplary LED driver circuit, which adjusts the voltage output signal from the energy scaler circuit so that none of the LEDs operate at more than approximately 20 mA or alternatively 25 mA per LED, which could overdrive the LEDs and cause early failure. All during the night time hours, the LED driver circuit continues to provide battery power to operate the LEDs at a constant level of current consumption. The LEDs are connected to the LED driver circuit through jumpers J10 and J11 located at the lower right hand corner ofFIG. 15 . If the battery voltage decreases down to 3.0 VDC due to power consumption by the LEDs, then the LED driver circuit turns down the current consumption by the LEDs regardless the input from the scaler energy circuit to extend the LED operating time. If the battery voltage continues to decrease down to below about 2.8 VDC, the transistor Q2 turns off the LEDs to conserve some of the battery energy and avoid over-discharging the battery. – FIG. 16 further illustrates the battery protection features of the control c
# PREMA Semiconductor Releases New Boost LED Driver For Solar Lamps – New Products Source: Blog/Web URL: https://eepower.com/new-industry-products/prema-semiconductor-releases-new-boost-led-driver-for-solar-lamps/ Author: Jeff Shepard Date: 2007-12-10 PREMA Semiconductor Releases New Boost LED Driver For Solar Lamps PREMA Semiconductor GmbH has extended its family of LED drivers with a boost driver for solar applications. The new PR4403 drives and controls white LEDs out of one single battery charged by solar cells. It uses the connected solar cells to detect daylight. LED solar lamps operate with automatic LED control depending on the ambient light level. The battery is charged by solar cells. According to the company, this normally requires several components like Schottky diodes, capacitors, resistors, two or three rechargeable battery cells and a photo resistor. In contrast to this standard solution the PR4403 saves several components, as it is able to drive the current for the white LED out of a single rechargeable battery cell. The expensive photo resistor is also claimed to be no longer needed. A supply voltage of down to 0.9V is sufficient for the IC to drive a current of up to 40mA independent of the input voltage. The value of the external inductor defines the LED current. Instead of the photo resistor, the solar cell is directly connected to the IC for daylight level detection, and an optional resistor sets the light threshold. Depending on the voltage at this conn
the output voltage of the driver using a DC voltage signal provided by the DC power source, a current flowing through the first inductor, a switching frequency of the first switch, and a duty ratio of the first switch. – the device may further include an electro-magnetic interference (EMI) filter operatively connected between the DC power source and the converter, and configured to eliminate high frequency components of a DC voltage signal from the DC power source. – EMI electro-magnetic interference Landscapes – Circuit Arrangement For Electric Light Sources In General (AREA) Abstract A dual mode constant output current LED driver is capable of operating with a very wide range of input direct current (DC) voltage. This provides an effective topology for a wide range of constant output current LED drivers, and allows for changing the number of connected LEDs without negatively impacting the output current. The LED driver includes a converter and a mode selection circuit that control the modes of the circuit based on the voltage. The converter and mode selection circuit operate in a buck-boost mode when the output voltage of the LED driver is less than the DC input voltage plus a first threshold amount, and in a boost mode when the output voltage of the LED driver is greater than the DC input voltage plus a second threshold amount. Description The present disclosure relates to power supplies suitable for driving light emitting diode (LED) lighting systems as well as other elec
the electrical power supplied from the external power source 213 . – a legacy luminaire 202 may optionally include dusk-to-dawn and/or motion sensing control mechanism or circuitry 216 and one or more optical sensors 218 . – the optical sensor 218 can take any of a variety of forms, including light sensitive or light responsive photosensors, cadmium sulfide cells, photodiodes, phototransistors, ambient light sensor integrated circuits currently commercially available. – the control circuitry 216 may be an analog circuit, digital circuit or may include both analog and digital circuit components. Again, a conventional commercially available luminaire with an integral control mechanism may be employed. – the dusk-to-dawn and/or motion sensing control mechanism or circuitry 216 can implement both dusk-to-dawn, and optionally motion or proximity based control. – the control mechanism or circuitry 216 relies on signals from the optical sensor 218 to implement motion or proximity sensing only during a period after a level of light or illumination in the environment has fallen below a turn ON threshold (e.g., 10 Lux) and before the level of illuminations exceeds a turn OFF threshold (e.g., 30 Lux). – the control mechanism will turn the light source(s) 204 ON for a period of time in response to the detection of motion between dusk and dawn, turning the light source(s) 204 OFF after the period of time. – the turn ON and turn OFF thresholds could be equivalent, such would likely produce
D4. The collector output terminal 32 of the switching transistor Q1 is connected to the signal input node 33 of the driver power control circuit 28. In the absence of sufficient ambient lighting, the output of the solar panel 22 does not provide enough driving current to develop a bias voltage that exceeds the turn-on threshold of transistor Q1. Consequently, under defined low-level ambient skylight intensity conditions (for example, less than 400 lux), Q1 is non-conducting (OFF), and a bias voltage develops across the power driver input node 33 as current flows through the Zener diode D8. The bias voltage is clamped at a turn-on voltage level by Zener diode D8, rendering Q2 conducting (ON), and applying operating power to the LED lamp group 64 (white light illumination) and LED lamp group 66 (yellow light illumination). When ambient skylight intensity rises above the defined threshold value, Q1 turns ON, pulling the input node 33 and base of Q2 to near zero reference potential. Resistor R2, which provides bias current to Q2, has a resistance value of 10 K ohms and is connected in series with the collector of Q1 through the input node 33, thereby safely limiting the current flowing through the collector and grounded emitter of Q1 to less than 1.5 mA under maximum photovoltaic supply conditions. Consequently, Q2 is rendered non-conducting (OFF), thus removing operating power from both LED groups during daylight operation. The electronic control circuits 26 and 28 ensure that a