Just got this killer explanation from Daniel Stern...must read!!! Looks like I might be getting Cibies if I can get Susquehanna to accept a return for my Hellas.
On Tue, 2 Nov 2004, Parcell, Jason wrote:
> I have a 2001 Jeep Cherokee, which uses the 6054 type sealed beam
> headlights. I previously had Sylvania Xtravision sealed beam
> replacement headlights, and upgraded to Hella E-code H4 headlamps. I
> upgraded based on some advice that I would have much improved nightime
> vision. After installing the E-Codes, I noticed they didn't put out
> nearly as much light as the sealed beams. The lighting pattern on low
> beam was nice, but still didn't put out much light, and the high beams
> put out a lot of light, but it was so focused, that I couldn't see the
> sides of the road. Could the lack of light output be a bulb-related
> problem, or is this just the nature of the E-Code lighting pattern?
It's the nature of *those particular* E-code lights that you installed. The Hella units are widely sold but -- in the 200mm x 142mm rectangular format you have as well as the 7" round format -- poor performers. The problem is worse than you state -- the low beam has a sharp cutoff, which is good, but that's all that can recommend it. The beam is too narrow, the hot spot too far over to the right, there's not much light within the beam pattern, and there's a *vexing* problem with those lamps related to beam
focus: The high beam hot spot is separated from the low beam hot spot by an excessive vertical amount. This means: Aim the low beams properly, and the high beams are focused up in the trees. Pull the high beams down where they can actually do you some good, and the low beams end 30 feet in front of the car. I exaggerate for illustration, but the effect is very real and not solvable; it's in the optics.
At this point you may feel as though you've been "burned" and not want to try and fix it, but if you're up for trying again with some good lamps, I do have the ones that were factory installed on Jeeps originally destined for export. They are Cibies, and they exhibit none of the problems your Hellas have.
Take a look at
http://www.torque.net/~dastern/Photometry/isocomparo.html .
These are isocandela diagrams for four different 7" round H4 headlamp units. I haven't got the 200mm units scanned yet, but they are very similar.
If you're not familiar with isocandela diagrams, these will look like random squiggles and lines. Think of it as a topographic or "contour" map of the correctly-aimed beam pattern. Each differently-colored line represents the threshold of a particular intensity level, with the color legend located to the right of the isocandela diagram. The 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 luminous flux (total amount of light within the beam), the maximum intensity and its location within the beam relative to the axial point (H,V) -- the less downward/rightward offset, the longer the seeing distance -- stray light outside the beam pattern 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
-- they're number one and number two in performance in this comparison. Focus on the bottom two diagrams, Cibie vs. Hella.
Things to notice about these two diagrams:
(1) 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.
2) The total luminous flux (overall amount of light) within the beam pattern is 695 lumens for the Cibie, 463 lumens for the Hella - the Cibie is 50.1% more efficient. (the TLF data is listed as "Luminous Flux" in the readings up above the isocandela diagram)
The high beams for these two lamps (isocandela diagrams not yet scanned
in) are somewhat 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, giving the problem described above.
So...whaddya say? Try again with good lamps?
DS