Automatic Street Light Circuit
Build an automatic street light circuit using a BT136 triac. Lights turn on at dusk and off at dawn using an LDR sensor for energy-efficient operation.
BT136 automatic street light circuit
BT136 is an automatic street light circuit that switches on the lamps when the sun goes down and switches off when the sun comes up. The LDR detects the surrounding lig, nd drives the triac switch, removes the manual operation, and conserves power.
BT136 AC light controller
Automatic Street Light Circuit with BT136 Triac is a design of a circuit that automatically switches on street lights at night and off in the daytime. The circuit also incorporates the use of an LDR (Light Dependent Resistor) to measure the intensity of ambient light. Under sunlight, the LDR detects the sun, turns the triac off, and the lamp is turned off, which is the daytime. As the dusk continues, the LDR resistance increases, causing the BT136 triac to turn on and the lamp to light. The BT136 triac is a high-current AC switch that is appropriate in the case of lighting 220 V AC lamps without mechanical relays. The circuit is a convenient, economical, and safe street light, garden light, or even pathway light. It does not need a lot of parts, and only a handful of components (BT136, diac, resistors, capacitors, and LDR) are needed to construct and maintain.
Work / Installation (Inputs → Outputs)
- AC Input (220V) powers the circuit.
- LDR sensor with resistor network senses day/night light.
- Triggering diac & BT136 triac switch the AC load.
- Lamp Output turns on automatically at night and off during the day.
- Mount LDR facing open sky to detect sunlight accurately.
Testing & Final Adjustments
Connect the power supply and AC lamp after connecting them. Check in the daytime to make sure that the lamp is off. Darken the LDR, and the lamp is expected to turn on. Use the LDR series resistor to alter the value of the light sensitivity threshold in case it switches too soon or too late. AC connections should be well insulated to avoid shocks. The lamps of high watts should have a heat sink attached to BT136 or the snubber circuit to avoid voltage spikes. Ensure that switching is not done with flickering. When stable, the circuit is mounted in a waterproof case to be fitted outside. Periodically monitor the LDR and connections for the accumulation of dust or water.
Frequently Asked Questions - Automatic Street Light Circuit:
What is BT136 used for in this circuit?
It acts as an AC switch to turn the street lamp on/off automatically.
What sensor detects day and night?
An LDR (Light Dependent Resistor) senses ambient light intensity.
What AC voltage does it handle?
It typically works with 220V AC lamps.
Can it be used for LED street lights?
Yes, with proper load and snubber protection for LEDs.
Does it save electricity?
Yes, the lamp only operates at night, reducing energy consumption.
How to adjust sensitivity?
By changing the series resistor with the LDR to set dusk/dawn threshold.
Is a heat sink required?
For high-wattage lamps, yes, to prevent BT136 overheating.
Can this work outdoors?
Yes, but the circuit must be in a waterproof enclosure.
Is the circuit complicated?
No, it uses only a few components and is easy to assemble.
Can it handle multiple lamps?
Yes, within the triac’s current rating; use multiple triacs for higher load.
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