H4 Plus Bulbs vs. High Wattage Bulbs, An Easy Choice

H4 Plus Bulbs vs. High Wattage Bulbs, An Easy Choice
by Daniel Stern, Vehicle Lighting Consultant

With upgraded wiring and relays in the headlamp circuit It's tempting to
grab for big wattage numbers, but for a sturdy collection of good
reasons (more info on request) it's usually counterproductive. Please
see bulb test results posted by my colleague Virgil at
http://www.candlepowerforums.com/vb/showthread.php?392498-Interesting-headlight-bulb-test-results
. Note the performance difference, especially on low beam, between the
standard bulb (bulb "A") and the high-wattage bulb (bulb "D") is not as
good as with the high-luminance +90 standard-wattage bulb (bulb "C").

As wattage increases, the size of the filament necessarily increases, both
in length and in diameter. This has a strongly negative effect on beam
focus -- the more closely the filament approximates a point source of
light, the better the beam focus, and the greater the size of the filament
the poorer the beam focus. Effective seeing distance plummets. At the same
time, foreground light goes to nuclear levels, which does two things at
the same time:

1) It fools you into thinking you've got "excellent" lighting. We humans
are very poor subjective judges of our visual performance; it's very easy
to create situations in which we think/feel we can see much better (or
much worse) than we actually can.

2) It absolutely kills your distance vision. The brightly-lit foreground
causes your pupils to constrict, with the result that you can meaningfully
see all the irrelevant stuff going on within 50 feet of the car, and
beyond that, you're effectively blind.

Also, the higher heat output from the high-watt bulbs greatly
accelerates the cooking-to-death of the shiny stuff that makes the
reflectors reflective. As you know, headlamp reflectors are shiny by
dint of a super-thin layer of vapor-deposited aluminum with a super-thin
protective clear topcoat. With years of headlamp usage the topcoat
eventually breaks down and allows the aluminum to begin oxidizing.
Optical degradation of the reflector is grossly advanced well before you
can see it with the naked eye (which is sometimes not possible), though
looking at it wouldn't do you much good; by the time the reflector has
degraded enough to be described as "just a little imperfect" the lamp is
past dead. For mental calibration on this point: even the most costly,
beautiful chrome plating, the kind that makes bumpers look 10 feet deep
on a show car, is only about 67% reflective. That's not nearly good
enough for optical purposes; an as-new headlamp reflector is over 99%
reflective, and there is no bulb that can compensate.

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Daniel Stern is an expert vehicle lighting consultant based in Vancouver, British Columbia, and Seattle. He serves as an expert witness, actively participates in technical standards development and research bodies, has contributed text to regulations in several countries and territories, and has attended the United Nations vehicle lighting regulation working group at the invitation of its president. He collects technically and historically significant car lamps, helps drivers safely upgrade their cars’ lighting, and serves as Chief Editor of the industry’s technical journal, Driving Vision News