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Replacing headlamp bulbs in pairs?
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Sat Sep 19, 2020 3:17 am    Post subject: Replacing headlamp bulbs in pairs? Reply with quote

Earlier on today I had to change a headlamp bulb on the modern. No issues there; it's a sensible design and bulb changes take a couple of minutes with no need for tools. New bulbs only came as packs of 2, so when I got home I was thinking of where to stow the spare bulb so it wouldn't be broken or lost for good, when I spotted the message on the back of the cardboard that bulbs should always, apparently, be replaced in pairs. I never have when simply replacing a blown bulb with another of the same type - to my mind it's unnecessary and would increase the chances of having both bulbs fail at the same time and leaving me stranded (and yes, that did happen to me once).

Does anyone know why it would be recommended to change headlamp bulbs in pairs, and does anyone actually do this? I suspect it's just a ruse to sell more bulbs but I'd be interested to hear your thoughts.
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roverdriver



Joined: 18 Oct 2008
Posts: 1210
Location: 100 miles from Melbourne, Victoria, Australia

PostPosted: Sat Sep 19, 2020 7:59 am    Post subject: Reply with quote

I believe, as you do- better to have one headlamp than none at all!
I know that older incandescents did become less bright with age, and so changing for two bright and brand new ones could be good. I don't know how that works with modern lamps.

In my days of Model A ownership, I carried a spare lamp in a box under the driver's seat, along with a set of points and a couple of other odds and ends, and never had a need to change both bulbs at the same time. Nowadays, with P4 Rovers, I have a spare in the glovebox., and just change one at a time as needed.
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Sat Sep 19, 2020 8:35 am    Post subject: Reply with quote

Headlamps on post 1991 vehicles are supposed to be a "matched pair".... I suppose in theory different bulb manufacturers bulbs may have slightly different characteristics?

Its a gift rule for the bulb manufacturers to enable them to sell more bulbs! If your headlamps look the same after the single bulb has been changed, I wouldn't bother changing the other.

Dave
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Penman



Joined: 23 Nov 2007
Posts: 4750
Location: Swindon, Wilts.

PostPosted: Sat Sep 19, 2020 8:40 am    Post subject: Reply with quote

Hi
I did once, in a Mini, have both dip beams fail within about a mile of each other.
Middle of the night in darkest Wales, fortunately i was able to proceed on mains until I reached somewhere with enough light to enable me to fit the one spare I had in the O/S light.
Those were the factory fitted bulbs that had failed together.

I keep 2 spares in the boot now, which reminds me, I need to get another one today because I had to fit one yesterday.

At least with the V40 I not only have the spares kept in the boot, I also have the last ditch option of moving a main beam bulb into the dip beam lamp.
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Peter_L



Joined: 10 Apr 2008
Posts: 2680
Location: New Brunswick. Canada.

PostPosted: Sat Sep 19, 2020 11:30 am    Post subject: Reply with quote

I am not sure about the logic, please correct me if I am wrong. After purchasing 2 new bulbs, because they are packed in 2's, why not fit them both and carry the good used one as a spare ?
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alanb



Joined: 10 Sep 2012
Posts: 516
Location: Berkshire.

PostPosted: Sat Sep 19, 2020 2:29 pm    Post subject: Reply with quote

Peter-L
that is what I do, change the pair and keep the good old one as a spare, Last time I changed the bulbs it was to upgrade to high performance bulbs, nothing wrong with the old bulbs just trying compete with these new LED’s
PS
(any one want to buy 6 used bulbs😄😄)
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petelang



Joined: 21 May 2009
Posts: 442
Location: Nottingham

PostPosted: Sat Sep 19, 2020 5:31 pm    Post subject: Reply with quote

Call me a cynic but, I bet the only reason they suggest you change them in pairs is to sell you more bulbs.
We live in a world of mass production and they need to keep churning out the stock.
Peter
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Penman



Joined: 23 Nov 2007
Posts: 4750
Location: Swindon, Wilts.

PostPosted: Sat Sep 19, 2020 6:26 pm    Post subject: Reply with quote

Hi
petelang wrote:

We live in a world of mass production and they need to keep churning out the stock.
Peter

Same reason Ford handbooks around the 80's-90's told you NOT to depress the button when apply the handbrake.
They weren't wearing out the rachet and pawl at the required rate.
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Bristols should always come in pairs.

Any 2 from:-
Straight 6
V8 V10
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alastairq



Joined: 14 Oct 2016
Posts: 1950
Location: East Yorkshire

PostPosted: Sat Sep 19, 2020 11:32 pm    Post subject: Reply with quote

What about the " time" factor?

Replacing a failed head lamp bulb to remain road legal is the important aspect.
On a working vehicle, when only one light has failed, makes the changing of its partner a waste of precious...... and possibly, paid for, time.

I wonder whether the packaging of two bulbs together isn't a way of getting more profit from an item that may have cost but pennies in the first place?
Flogging two bulbs when only one was really needed? A bit like Colman's making their fortune from the mustard we leave on the plate?
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Sun Sep 20, 2020 3:27 am    Post subject: Reply with quote

Looks like I'm not alone in suspecting the motive of this piece of advice! If there is any difference in performance between old and new bulbs it's invisible to the Mark 1 eyeball and thus irrelevant.

The time I had both bulbs fail at once they turned out to be an unmatched pair, one marked Ring and the other (IIRC) Osram, I did suspect an underlying fault of some kind but it never happened again. I had taken a return trip over the old Severn bridge earlier that day and wondered if it could be related to the rather rough surface over the bridge - it's been a case of patch and mend for decades now as proper resurfacing would be such a massively expensive job, never mind the disruption.

Peter_L: your suggestion of changing both bulbs and keeping the odd working one as a spare has one problem, to my mind. With modern halogen bulbs you're not supposed to touch the glass, remember? I'm not entirely sure why and maybe it's all nonsense anyway, but I reckon that removing a working bulb to replace it with a new working bulb, to possibly replace the old working bulb somewhere down the line gives me a pretty good chance of accidentally getting my greasy fingers on the glass leading to a premature failure at some point. Best to leave well alone I reckon, why bother fixing something that's not broken?
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lowdrag



Joined: 10 Apr 2009
Posts: 1585
Location: Le Mans

PostPosted: Sun Sep 20, 2020 4:19 am    Post subject: Reply with quote

Don't I seem to recall an article about modern cars and how many hours it takes to change a headlamp bulb? I have an idea that an Audi came off worst with bumper and grille removal needed and a five hour labour bill at the end of it all. Perhaps someone will correct me. Memory isn't what it was!
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alastairq



Joined: 14 Oct 2016
Posts: 1950
Location: East Yorkshire

PostPosted: Sun Sep 20, 2020 8:48 am    Post subject: Reply with quote

Quote:
With modern halogen bulbs you're not supposed to touch the glass, remember? I'm not entirely sure why and maybe it's all nonsense anyway,

It's to do with oils.
The modern bulbs burn at a much higher temperature than thos eof old.
By touching the glass with a finger, oils from our skin create a localised 'hot spot' on the glass, which can lead to the glass getting super hot, adn failing.

In my last job, basic vehicle components, their care and replacement, was a small, but vital part of our 'students' training.
Such as how to change a headlight bulb, and what not to do?
It was often arranged with our workshops to try to 'catch' a halogen bulb that had its glass bulged at a hot spot, but not actually broken[exploded]....wemanged to get a few like this..all due to handling with bare fingers when installing. Quite dramatic!

It's also why the better quality brands pack their bulbs with a foam, or cardboard, tube over the glass bit.....not so much for protection, more a a means of handling without touching.
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.
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