[Glifford]

This was basically because of the notion that painting a black strip on the top will reduce glare (esp. in high beam) to oncoming drivers. Another similar practice was to apply a black dot in the centre of the headlamp, right in front of the bulb.

This was enforced randomly and there used to be roadside squads (at least in Maharashtra where I grew) where cops would stand with painters with cans of black paint in one hand and a brush in another. If you did not have the strip they would clumsily slather your headlamp with some wet paint (at times even messing up your vehicle paint with this mess or fingerprints from the painter).

I think this was the stupidest thing ever done and a knee jerk reaction to a genuine problem without any scientific thought whatsoever!

The reason being, any headlamp is not a homogeneous source of light by itself. It is a complex engineered part, that consists of a light source (bulb), reflector and lens. The lens did the job of dispersion and were different for the right side and left. The dispersion elements can be clearly seen here:

Originally Posted by RedTerrano

Attachment 2104996

Slowly engineering and manufacturing progressed enough that dispersion could be handled by the reflector and the lens could remain clear!

Automobile headlamps have had reflectors since time immemorial (even before electric lamps, when they were oil powered).

Now coming to why masking off the top is a bad idea!

Remember the light "throw" is done by the reflector, NOT the bulb. So in a parabolic reflector. The light going downward (to the ground ahead) is reflected by the upper part of the reflector (and emerges from the top part of the headlamp). And vice versa for the light going upward.

This can be clearly seen in the pic shared by Saikarthik below:

Originally Posted by saikarthik

Attachment 2104911

Hence by painting the top half of the headlamp, you are actually blocking the light that is going downward to the road ahead, while completely ignoring the glare going upward and actually blinding oncoming drivers!

And the net result is drivers cannot see the road well enough, so inadvertently switch to high beam and thus blind oncoming traffic more as the lower part of the headlamp is not blacked out!

Same goes with black dot in the centre of the headlamp. The glare hardly comes from the bulb itself, rather from the reflector around it. That said, most halogens have a blackened end anyway!

[srishiva]

Oh this was not that long ago. There used to be volunteers from rotary and other clubs who did this for vehicles which did not have them. Police used to insist on this too. Reasons were not to blind the oncoming traffic. Guess they did not insist on using low beams but made this mandatory

[silverado]

Isnt the purpose similar to GJ state yellow strip thing on RHS headlight?
Maybe since there was no headlight leveling switch this was a Jugaad way of reducing the spread on upper side.

Looked weird on mordern cars like Esteem and Cielo.
It was a common thing on Buses and trucks back then.

In fact i remember there used to be a black dot painted right in middle for same purpose.

[sramanat]

As has been explained already in the forum, it was to reduce the glare for the driver coming in the opposite direction. Tamil Nadu had a rule to have a black dot in the middle. An article from the Hindu 4 years back has quotes from senior officials on this. It talks about an automatic dipper in developed countries which lowers the light beam in case there is an oncoming traffic. May be it is now standard in the cars being sold. With the streets and highways being lit up, this has largely gone away it seems.

[landcruiser123]

To prevent blinding is the only logical reason I can think of. It was probably due to a law in the era of ambassadors, padminis, and jeeps where vehicles had simple circular or rectangular shaped headlamps and parabolic reflectors behind them.

Implementation reduced in the late 90s and early 2000s with GJ being the exception. AFAIK, we had in our Maruti 800 in 1998 but our Qualis did not in 2000. No trouble from the cops in KA & TN ever.

The only other place where it can be useful is between UK & mainland Europe where people now install beam adapters to allow them to drive on the 'wrong' side of the road without blinding oncoming traffic.

[Rajat347]

I had this on my Bajaj Super and M800.
The logic was to prevent spread of light beam and make it more focused. Frosty reflector and lack of clear lens headlights glass was there and hence lights were not powerful.

[Salil]

Ironic, considering it is the the lower part of the reflector that produces the high beam, while the upper part of the reflector-lense combination actually produces the low beam!

[BackstraightBoy]

Whatever the flawed logic behind the regulation, I had seen it as a nice space for a custom sticker of one of my then-favourite brands! Photo from 2007.

[patwardhan]

I think even today cars registered in Gujarat have their headlights partially masked. It should be a mandatory feature, I fail to understand how any state can decide on the safety norms. It has to be governed across states. With the competition among owners to install powerful head lights, this will deter as it will have limited obstruction to oncoming traffic

[SatyRoy]

As per my early memories from the childhood, black stripes on trucks (family transport business) are to minimize the glare from the high beam. Not sure if it had any other use as well.

[rahul_kej]

I hope by now you have got your answer for the black strip on the headlight back then, though little off topic but am surprised that no one put on this question that do you have any plan to restore those too iconic classics specially the Tata Estate or they will stay abandoned for ever or any plans of scrapping?

[Mahesh Babu]

Even though I have no idea about the exact dates, i distinctly remember this as mandatory in Kerala in eighties and nineties. This rule was not there in 1984 when I got my Yezdi (but it was compulsory to have a black spot about 2cm in diameter in the centre of the headlight) but was forced to blacken the upper half soon after due to a new regulation. Police used to enforce the rule very religiously and fines were levied on defaulters. The rule was in place till late nineties, my Zen(1996) sported it initially. The purpose was to avoid blinding the oncoming traffic with your headlights while still illuminating the road in front.

[Mainali]

I always wondered, why almost every vehicle in Sikkim had this. One explanation which a taxi driver gave me was a vehicle approaching uphill even with high beam will have his high beam cut off a little, helping the other vehicle descending, considering the entire state being a hilly state.
The theory didn't quite hold out when I got my first bike pulsar 220 with its curved head light design. I was not sure how am I going to put that black tape/paint and I never did. I was never stopped by cops ever. I guess it was something people in Sikkim got use to it and since it was helping them out in some way and bikes being less common in state, no one cared.

It's interesting and I will try to research how the black tape/paint on top of headlights became prominent in Sikkim. Even new cars till 2010 use to have them. There has to be a story or something behind people putting them up. I will share the details once I have them.

[King_pin09]

Originally Posted by Salil

Ironic, considering it is the the lower part of the reflector that produces the high beam, while the upper part of the reflector-lense combination actually produces the low beam!

Automotive optics back then, were not as advanced as they are today.
With advanced Computer algorithms, design and development of complex optical device is possible and therefore the headlamps these days perform quite differently from early days. Many vehicles back then managed achieving the low and high beams through single bulb containing two separate filaments. These filaments were made from different metals and had separate circuits. The reflectors and the lens served as diffusers while provided basic directional assistance to the light rays.

[ontheway]

These black strips were still prevalent not so long ago, I think they could still easily be spotted on the vehicles well in late 2000's.
I remember asking one of the taxi drivers why these were there on his car, and he said, technically they should restrict high beam of the car but practically it's just to avoid getting haggled by the cops and give them one less reason to stop us.
So as many have already pointed out, these strips actually didn't serve any purpose, but were checked by cops, especially on outstation cars when visiting hilly areas.