I just found about the technology of headlights today, I am just gonna share it here in this small post.

A vehicle has two modes. High beam and Low beam. Low beam is used for inside city navigation and high beams for highway navigation.

Let’s start with convex lens. If we place, an object at infinity, the image will be at focus. Conversely, an object at focus will generate image at infinity. We got our long sight concept right there. Just place the bulb at focus of the convex lens, light will reach out very far.

How do we get low beam then ? Place bulb far away from lens ? No. Just, keep the bulb with it’s x-position on focus and just lift them up the focal plane. There you go. We can even go further and shift it towards left or right of focal plane depending on the nature of traffic in the region. In addition to that, the inside of the lamp is coated with high reflective materials.

We also need switching relays to change between high and low beam. High beam is high intensity and draws a larger load from battery compared to low beam. If we want to switch to that configuration, we need a bigger switch. A smaller switch will burn down because it’s fuse won’t have that high a current rating. But if we use a bigger switch, how do we get it to push and pull ?

This switching operation is undertaken by a relay. This relay circuit uses a smaller switch to accomplish the trigger of bigger switch using electro-magnetic energy. This utilizes a small switch, an electro-magnet wound on a spring coil connected to big switch.

When we flick the switch, the input current flows through the spring, the electromagnet pushes the spring down, and the bigger contact switches on the High Beam load. When the spring current ceases to flow, the bigger circuit breaks. I haven’t drawn the low beam circuitry, input switches to low beam filament circuit as the high beam circuit is open.

I found this to be a smart piece of physics and engineering, Hope you did too.