Why Do Car Headlights Start Bright But Quickly Dim?"

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  • Thread starter Thread starter Himal kharel
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SUMMARY

Car headlights initially appear brighter upon starting the vehicle due to full power being supplied when the key is in the "Running" position. As the key is turned to the "Starter" position, the starter motor engages and draws significant current, causing a voltage drop in the battery due to its internal resistance. This results in the headlights dimming. Once the key is released back to the "Running" position, the headlights regain their brightness.

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Automotive technicians, electrical engineers, and car enthusiasts interested in understanding vehicle lighting systems and electrical behavior during engine start-up.

Himal kharel
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headlights on starting car are brighter . they immediately get dimmer . why?
 
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When you turn your key, the key passes "Running" position first, at which point, full power is supplied to the headlights. The key then goes to "Starter" position, at which point starter engages. Starter draws a lot of current, which results in a battery voltage drop (due to battery's internal resistance). Because of that, lights grow dimmer. Once you let go of the key, releasing it back to "Running" position, the lights should go back to being bright again.
 

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