Found a 7" Bosch H4 motorcycle headlight (21071H) and was wondering if the lighting pattern is different than an auto headlight, and how they compare to cibies????????

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I know Dan will have a way more technical answer for you, but my experience with 7" sealed beam bike bulbs was that motorcycle bulbs were more resistant to vibration. I tried running a regular car sealed beam in my old 900 Kaw and it would shake the filament out in a day or 2.

Other than that, there seemed to me to be no difference in brightness or pattern.

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Official Cookie and Mater Tormentor.

Slantzilla is partly correct. The Bosch motorcycle headlamp is optimized for resistance to the particular kinds of vibration found in motorcycle service, but this comes at the expense of certain performance characteristics. The motorcycle unit is also less water-resistant, produces more upward stray light that causes backdazzle in bad weather, and lacks the heat-compensating bulb seat found in the car/truck version of the lamp. That last difference is significant; it means the beam focus changes (worsens) as the lamp heats up normally. The regulations in place worldwide for motorcycle headlamps are considerably less stringent than for car/truck headlamps, so pretty much all the manufacturers' motorcycle-version lamps are of cheaper construction.

A lot of people think all 7" round H4 lights are equivalent, because they look at the shape of the cutoff on the wall and think they all look alike. Nope! The shape of the cutoff is determined by the technical regulations; what's much more important is how much light is distributed (and how/where) under the cutoff. Even if we disregard the off-brand junk from China and India, there are enormous differences in performance among major-brand headlamps.

Take a look at the differences in performance between Marchal H4s and Cibie H4s (and the commonly-available Hella units, which are almost identical to the Bosch car/truck lamps).

The link takes you to isocandela diagrams for four different 7" round H4 headlamp units. Why not photographs? Because photographs of beam patterns can be very misleading even if the photographer has the best of intentions, because pixels and film work in a fundamentally different way than human eyes. First, let's look at more objective comparisons of different headlamps' beam performance. The way to do that is with isocandela diagrams, which are generated by a machine called a photogoniometer that measures the intensity of light produced by the headlamp through a large range of vertical and horizontal angles. are just like topographical (elevation) maps, except the squiggles and lines represent amounts of light, instead of elevation above sea level. The beam pattern is correctly aimed as it would be on a car on the road, and each differently-colored line represents the threshold of a particular intensity level. Each diagram is plotted on a chart calibrated in degrees. Straight ahead is represented by (0,0), that is, zero degrees up-down and zero degrees left-right.

To get a mental approximation of the units and amounts under discussion
here:

Parking lamp: About 60 to 100 candela
Front turn signal: About 500 candela
Glaring high-beam daytime running lamps (e.g. Saturn): 8000 candela

The parameters to pay attention to are the maximum intensity and its location within the beam relative to the axial point (straight ahead, dead-center of the diagram chart)—the less downward/rightward offset, the longer the seeing distance—stray light outside the beam pattern (primarily above the horizon) and effective beam width (contained within the dark-turquoise 500 candela contour)

The two lamps at the top of the page are no longer produced, which is sad, because they're number one and number two in performance in this comparison. The one at the top is the Marchal H4, which I do have the last production run of, on my warehouse shelf. Note its extremely wide beam pattern, intense and well-placed hot spot, and very well controlled upward stray light.

The second lamp on the page is no longer made _and_ not available. It's the Cibie Z-beam. The Indian made "reproductions" on eBay are trash.

The third and fourth diagrams are Cibie and Hella 7" round H4 lamps, respectively. The Hella unit is almost identical in performance to the Bosch car/truck lamp. The Bosch motorcycle lamp produces a similar beam with a lower-intensity hot spot located farther over to the right (shorter seeing distance) and a great deal more upward stray light (more backdazzle in bad weather).

Things to notice about these two diagrams:

The Cibie produces a much wider beam pattern than the Hella. The 1000 candela line of the Cibie's beam pattern extends from 25 degrees Left to 25 degrees right, while the 1000 candela line of the Hella extends from 18 degrees Left to 20 degrees Right. At a distance of 50 feet from the car, this means the 1000 candela-and-brighter portion of the Hella's beam is 10.5 feet narrower than that of the Cibie. The 300 cd contour of the Cibie's pattern is far wider, extending from 43 degrees Left to 50 degrees Right, compared to 26 Left to 25 Right for the Hella. This means the overall useful width of the beam pattern at 25 feet from the car, as perceived by the driver, will be 40.7 feet for the Cibie and 22.3 feet for the Hella.

The high beams for these two lamps (isocandela diagrams not yet scanned in) are pretty similar in overall performance and amount of light. The critical difference is that the Cibie's high beam hot spot is located closer to (0,0) and closer to its low beam hot spot. The Hella's high beam and low beam hot spots are separated by a fairly large vertical amount, such that setting the lows where they belong results in most of the high beam light going up in the trees, but pulling the high beams down so they send light straight ahead puts the low beams 10 feet in front of the car. This is less of a problem with the Bosch units than with the Hellas.

Bottom line: no, the Bosch motorcycle headlamp is not a wise choice for car/truck service, and no, all 7" round H4 lights are not alike.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.