Technical MGB discussion
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Re: Relays

Post by ChargedAutoGT » Sat Aug 01, 2020 11:29 pm

"although they seemed brighter the beam was poor"

I am trying to visualise what you mean by this please? are you saying bright, but the beam does not project as far ahead? or something else?


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Peter Cresswell
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Re: Relays

Post by Peter Cresswell » Mon Aug 03, 2020 11:25 am

"although they seemed brighter the beam was poor"
I think to understand this, you have to separate the bulb from the glass of the headlight unit.

As an example, a lighthouse typically these days uses a 250W halogen bulb. The light from this would be scattered 360 degrees from the top of the lighthouse. In order to concentrate the light and direct it into a beam, a lens is used which a rather complex system of prisms. This enables a concentrated beam of light to be seem 20 - 25 miles out at sea.

In the car headlight system, the bulb is obviously similar but much smaller. Again the light would be scattered everywhere and indeed would have difficulty illuminating an average sized living room. The lens in the case headlight units has two parts - the reflector and the glass lens. The reflector is parabolic and concentrates the light into a single beam, which then passes through the glass lens. The pattern on the glass dictates how the road in front of the car is illuminated at night. The design of the pattern is complex and it has to produce a pattern of light which doesn't dazzle oncoming drivers but still illuminates the kerb on the nearside. It also has to 'throw' light further down the road when on main beam, so the driver gets as early warning of hazards ahead.

It is the design of the pattern on the glass that produces the effect of "although they seemed brighter the beam was poor" which means the drivers view of the road ahead is compromised. So not all headlight units are the same and unfortunately it is a case of you get what you pay for, and whilst some manufactures spend a lot of time and effort to produce a headlight unit to provides excellent night vision, others don't!
I also suspect that the quality of the glass and the moulding that forms the pattern also plays a part in this.
The bottom line is that upgrading the bulbs to better modern technology might be disappointing as the beam shape hasn't changed.

Hope this helps as quick explanation of something that is quite complex.
1969 MGB Roadster
2020 MG HS Exclusive
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Plus 34 other cars since 1965

Allan T
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Re: Relays

Post by Allan T » Tue Aug 04, 2020 1:30 am

Hi Brian,

I think Peter has nailed it beautifully and thoroughly as usual.

But just to repeat what he says in a slightly different way, Duncan Rickards of Classic Car LEDs emphasises the importance of the reflectors and lenses you use with your new LED bulbs.

He sells and recommends Lucas, and I think you'll find he likes Cibie and Hella too.

I've no experience and no knowledge of the Owners' Club hardware - unless they're Wipac, in which case I wouldn't touch them with a bargepole.


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