Why do older cars have a kind of line pattern on the headlights and it is a little blurry while newer cars have nice and transparent headlights?
In: Engineering
Normal driving light (not high beam and not parking lights) has to be asymmetrical, meaning the beam of light needs to light up the road differently. Towards the middle/traffic, the light has to hit the road sooner than towards the side. This is to not blind the oncoming traffic, yet provide enough light (and give you enough time) to react to pedestrians/bikes/animals that could be on the side of the road.
One could now think that the lightbulb towards the middle is just pointed lower than the one to towards the outside. But that’s not the case. Both bulbs are shining on both sides. Asymmetrical.
On older cars, this effect was achieved by making lines and making the glass thinner and thicker different places, it creates this difference in where the light beam hits the road (if you know about the lights refraction in glass).
Today, this is done in a much more technical way, thus the lines are not needed anymore (also making it much cheaper to replace a broken headlight glass).
[deleted]
The patterns in the lens are actually tiny _prisms_ designed to manipulate _images of the filament_ to correctly illuminate the road. Usually, when people think of prisms, they think of [this](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcShjX12oAzh-YvAWHE4vD6cvn7-OufXNR-CPhONEpUrynvYe8Dz&s). Yes, that’s a prism. But it’s only one type of prism. The line pattern you see on older headlamps represent other forms of prisms–prisms used to create _image transformations_ such as flips, rotations, etc. Why do we want to effect image transformations? Keep on reading!
—-
We’ll start with [a simplified model of the headlamp.](https://i.imgur.com/VLWuNzn.png) The relationship of the filament and the reflector is highlighted by this simplified model: the filament emits light, which is reflected onto the road.
Fact: _Images of the filament_ are reflected onto the road. [A car’s beam pattern is _the composite of many filament images._](https://i.imgur.com/RVlaopd.png)
Explanation: It’s really no different than if you walked into your bathroom and looked at the mirror–the _image of your face_ is reflected back into your eyes, into my eyes since I’ll be standing behind you, and even onto the bathroom wall behind you. The only difference is that your face isn’t exactly glowing hot enough to _emit_ light, so by looking into the mirror, you aren’t really making the wall behind you any brighter. But a filament obviously glows hot enough to emit light, so its reflected image will light up the road.
However, just putting images of the filament on the road isn’t enough. The filament images [are carefully “remapped” by the lens and onto the road.](https://i.imgur.com/Xu5UL5T.png) Those rectangles represent images of the (rectangular) filament. They’re placed at all sorts of locations and orientations. How did we rotate those rectangles?? How did we translate them vertically? How did we translate them horizontally? How did we move them all over the damn place??
Well, that’s where the patterned lens comes into play–those [prisms](https://i.imgur.com/9ws7pGj.png) are purpose-made to manipulate the image of the filament. The prisms “play” with the filament images to effect the necessary transformations.
—-
>newer cars have nice and transparent headlights
Advances in computational power enabled this. Older headlamps with the patterned lenses mainly relied on simple, paraboloid reflectors–unlike today, where we have _complex freeform_ and often [_segemented_ reflectors.](https://i.imgur.com/1b4JLLh.png) Look at all the _segments_ within that headlamp. The reflector surface is broken up into little “strips” and each of these strips has been individually tuned to manipulate the _filament image_ correctly without the help of lens prisms.
Now, we can specify the appropriate beam pattern and work backwards into a _complex_ reflector [that manipulates the filament image without the help of a lens.](https://i.imgur.com/76ujd9m.png) The geometric characteristics of each _segment_ can be manipulated to send filament images exactly where they need to go.
Send an optical designer back 40 years without today’s powerful computers and such a task–calculating the appropriate geometries for each of these numerous segments–would take literally years if not decades for a single headlamp.
Latest Answers