Your car has a 12 volt system and uses a battery to maintain that 12volts. However cars us an alternator to produce power to charge your battery (at a slightly higher voltage, usually 13.8 volts). However if the engine is running slower, the alternator stops charging the battery and your system goes back to it's 12 volt battery power and therfore 1.8 volts less. All the lights dim slightly, the heater will slow down, everything that uses electricity will be effected. A weak alternator will make this worse as does a worn, slipping alternator drive belt. Should probably be checked.
The headlights in a car usually dim slightly when the starter motor is used. This is because the starter generally pulls substantial current from the battery, and that causes the battery voltage to decrease.
However, they should not go too dim...
Excessiving dimming can be caused by a bad or undercharged battery, and bad starter, or bad wiring connections.
As you add more load, the load current increases. This causes an increase in the internal voltage drop taking place inside the battery, due to its internal resistance. The terminal voltage will then reduce by an amount equal to that increase in internal voltage drop.
Because when a car is started the starter motor draws power from the battery at the same time as the lights, leaving less power for the lights so they dim.
size of pupil becomes larger when you see in dim light
Because the cells in the retina of your eye that produce the sensation of color are insensitive to dim light, and images in dim light are perceived by other retinal cells that are less interested in color.
Before starting, if the lights are switched on, all of the current from the battery is going to the lamps, but quite a lot of electrical power is required to start the engine, particularly if the oil is thicker because it is cold. When the engine starts it drives the dynamo or alternator which sends extra current to the battery which can then send more current to the lights.
I have an idea
They Are Dim Because the d-cell being used does not produce enough energy to light them both
You should dim your headlights within 500 feet of the car in front of you. The rule of thumb is, if you can see another car, dim your lights.
100 feet
When you get 300 feet from the car coming ahead.
ldr sensor
Bad connection, bad ground, switch problem check the bulb are places to start
you might have a short in your alternator. In my car the headlights would dim when I put on the brakes or tried to use cigerette lighter to power up my phone.
i have two problems my dim headlights will not come on.and when go to put in gas it will flow back word make it seem like the car is full.
Your battery is weak, or your your alternator is not charging battery.
Usually dim headlights are caused by a poor ground connection.
100 yards
You need to periodically replace the headlights on your Chevy truck when the headlights start getting dim. You can purchase replacement headlights from retailers such as Parts Source.
At night a driver should dim his headlights when an oncoming motor vehicle comes within 1,000 feet. You should switch your headlights from full beam to dipped beam when a oncoming car passes. It is unsafe to leave your headlights on full beam as it blinds the driver of the oncoming car.