Hey all!

Bit of a random question which I cannot find on the internet....

Why does the glass on the front of headlights have a variety of lines on them when some others don't?

For example,

CLEAR


SMOKED/Lines



I hear of people changing to clear glass but would that not affect the lights somehow?

Help an ex-lepper!

I think its to position the light. Afaik, the light from the bulb rebounds from the reflector (the chrome looking part, on the inside) then onto the lense, then the small "lines" and grooves in the lense point the light down, towards the road.

Same concept as a Fresnel lens, isn't it?

Yeah, it's a fresnel lens. It focuses the light into a beam. Some cars have a normal lens right in front of the bulb, so don't need the grooves. You'll be more likely to find more grooves on older cars, where the bulb usually just sat inside the light housing - on newer ones, there's usually a secondary housing around the bulb (containing the lens), inside the main housing.

http://en.wikipedia.org/wiki/Fresnel_lens

The 'grooves' as you put it, are there to spread and reflect the light from the headlight bulb in the right direction to allow the best beam of light available to see where you are going at night without dazzling oncoming drivers.

You may see some foriegn cars that have deflectors, or what i use, which is a small shaped piece of insulation tape, cut to a marked pattern on the outside of the lense in order to deflect the light in a different direction so as not to dazzle people in europe as they drive on the other side of the road.

As everyone else has said, the lines are there to focus and redirect the light ahead in the pattern the designer wants.

However, the clear example you gave is a HID (High intensity discharge) headlamp. They are basicaly a projector style bulb with a balast and do not require a focusing lense because the light already leaves the bulb in a beam. The light around it is to compensate for the lack of short range lighting by the bulb, something only frosted lenses gives you.

My family's 6.5L turbo diesel van has ridged lenses and standard bulbs, but the lenses aren't frosted, this is so that the light will go as far as possible ahead of the vehicle, the unfortunate side effect is that the light doesn't scatter as much close by because of the lack of frosting on the lenses. I'm not sure why the designers did it this way, but we found a work around.

The ridging on the lenses is to scatter the light ahead, the frosting is to scatter the light closer to the vehicle so you can see more around the sides. Without one the light would be in too wide a beam farther out, without the other it would be too focused on the longer range and woulden't light up the area close to the front of the vehicle.

For this reason we have fog lamps set up for driving at night on unlit roads, this way we can use high beams with the unfrosted lenses to see far and use the fog lamps to light up more around the sides of the road. It basicaly light up the entire road so we can see everything. The lights go lowbeams/off when there are oncoming cars though, it would be crazy to run all that lighting in another drivers eyes.

Interesting, I knew about the various lens-effects but I never thought about the frosting scattering the light up close. Obvious really, when you think about it.

This is fascinating stuff guys, thank you!

Quote from DragonCommando :

However, the clear example you gave is a HID (High intensity discharge) headlamp. They are basicaly a projector style bulb with a balast and do not require a focusing lense because the light already leaves the bulb in a beam. The light around it is to compensate for the lack of short range lighting by the bulb, something only frosted lenses gives you.

So by installing a HID conversion you'd also have to change the glass? Or it just "doesn't work like that"

Quote from MR_B :

This is fascinating stuff guys, thank you!




So by installing a HID conversion you'd also have to change the glass? Or it just "doesn't work like that"

The bulb, reflector and lens are all designed to work as a combined unit to get the distribution of the headlight beam as required to meet manufacturers specs and remain within the law. Change one part alond and you'll mess one or the other up.

Quote from danthebangerboy :

.... without dazzling oncoming drivers.

Over here in the US, I'd swear the government regulations on headlights are such that they be designed to shine directly into oncoming driver's eyes as much as possible.

Im not a scientist, so i dont give a *shiz* about this Important is the light itself.

Posting in a topic to say you're not interested in the topic is one of the worst kinds of spam.