Update :-
Voltage drop is 1.45V.
Test 1.
Engine OFF.
Voltage at battery under load = 12.03 V
Voltage at LH High Beam bulb holder = 10.57 V
Difference = 1.46 V
Test 2.
Engine IDLING.
Voltage at battery under load = 14.07 V
Voltage at LH High Beam bulb holder = 12.61 V
Difference = 1.46 V
Had a look at the wiring to remind myself just how thin it is!!
Looks like a trip to get 4 relays, 4 bulb connectors and some nice thick wire!
Here is the table from the Daniel Stern site.
10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens ←Rated output voltage
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens ←Rated life voltage
14.5V : 1528 lumens
The Europeans take a slightly more realistic with their voltage ratings; they consider output at 13.2v to be "100%".
The loss curve is the same, though.
When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated light output.
When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be.
And when voltage drops to 85 percent (11.22v), bulb output is a paltry 53 percent of normal!
It is much more common than you might think for factory headlamp wiring/switch setups to produce this kind of voltage drop, especially once they're no longer brand new and the connections have accumulated some corrosion and dirt.
See the effect of the voltage drop when the engine is running from 14.07 to 12.61 Volts. This reduces the potential light output from 1356 lumens to 803 lumens, a 553 lumens drop.
Gerry
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