911 Best-in-Class ~ A Division of Audette Collection

The Best H4 Bulb - Tungsram +120 - Technical Information

H4 "Plus" Bulb Technology
By Daniel Stern

The non-plus standard H4 bulbs are built as a compromise, endeavoring to strike a balance between performance and longevity. The filament changes required to make a long-life bulb tend to reduce the beam focus, which shortens seeing distance and makes the light browner -- but lifespan is lengthened.

The opposite filament changes are made to create the "Plus" bulbs (+30, +50, +80, +90, +100, +120...). Lifespan is shorter, but the beam focus is better so the seeing distance is longer - and the light color is whiter and less brown.The lifespan difference is less stark than it might seem because the long-life bulbs not only start out dimmer, but they last (i.e., keep lighting up) long enough to lose significant amounts of their original output. The higher-performing bulbs burn out before they drop much of any intensity.


The above is from a Hella technical paper goes into some detail on the performance difference between a standard bulb and a "plus" bulb. When it was written, the state of the art was +30, so this is a comparison between a long-life and a +30 bulb. Additional research and development has brought us to the present where we have +100, +120, +130, +150 bulbs. There are two things to keep in mind:

1. This won't continue forever; there are certain hard physical limits of the technology.

2. A bigger plus-number doesn't necessarily mean a better bulb.Most all of the +130 and +150 bulbs have more and deeper blue tint on the bulb glass, especially in the area surrounding the high beam filament. Any amount of blue filtration sharply reduces the amount of light reaching the road in exchange for no benefit at all except a bogus appeal to fashion. Headlamps are life-safety equipment, not fashion toys, so this is a bad deal and those bulbs are best avoided.

Now, what about the blue ring just below the tip of the good +120 bulbs? That's actually completely different. The marketers say this is there to make a fashion statement with your headlamps, but it's really there for a stealthier reason: to cut the mean spherical output of the bulb down to legal levels as tested in an integrating sphere (the machine used to measure light output from a bulb to determine if it falls within the legally required range). The blue ring filters a part of the bulb that has nothing to do with beam formation because it's not located between the filament and the reflector. So it cuts down on the total light output from the bulb when all directions are considered, as in the sphere, without reducing the light output in the relevant directions as in the headlamp. In other words, the filament is pumping mad lumens through the uncolored glass where the reflector is looking. Clever trick. It works.

Unlike the higher power standard H4 bulbs, such as 100w, the Plus bulbs do not require a relay kit as they do not draw more current then the standard 65w bulbs. There is a big "but" however...

"Require" is squishy here -- if the wiring on the car is in good shape, then there won't be any problem provoked by these bulbs. However, any bulb will give more and better light with low-resistance feeds and grounds. The will bulb's lifespan will be shortened.