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Re: easy
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Posted by Strålkastaremann (more from Strålkastaremann) on Sat, 14 May 2005 08:05:59 Share Post by Email
In Reply to: Re: easy, Dan W, Fri, 13 May 2005 20:24:28
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The older Saabs tend to have fairly marginal headlamp wiring that causes a
large enough voltage drop to "starve" whatever bulbs you install, even
stock-wattage 60/55w items. You won't burn up the car or anything, but
your headlamps will be much dimmer and browner than they could be. Small
voltage drops take large bites out of headlamp performance. You can test
this yourself.

Conditions:

ALL headlamps connected - you may have to backprobe the sockets, but
removing the socket from the headlamp invalidates the test.

Headlamps of the same wattage you plan to use -- remember that halogen
H6054 sealed beams use 35w low beams, so the voltage drop found on low
beam with those would be lower than with 55w low beams.

Engine off, circuit to be tested (low or high beam) energized

First, connect your voltmeter across the battery + and - terminals. Record
the voltage reading, this is the battery voltage.

Connect your voltmeter positive lead to the battery (+) and the voltmeter
negative lead to the + terminal of whichever headlamp beam you're testing
-- use the bulb farthest away from the battery. With the lamps on, your
voltmeter will give a direct reading of the voltage drop. Write it down.

Then connect the positive voltmeter lead to the ground terminal of the
headlamp bulb, and the negative voltmeter lead to the (-) terminal of the
battery. With the lamps on, your voltmeter will again give a direct
reading of the voltage drop. Write it down.

Add the two voltage drop figures obtained, and this is the total circuit
drop.

Subtract the total circuit drop from the battery voltage to find the
voltage at which your bulbs are operating.

Remember, light output drops exponentially, not linearly, with voltage
drop. Small voltage drops = large light losses. The formula for
determining the change in light output with a change in voltage is:

lumens at old volts x [(new volts /old volts) ^3.4] = lumens at new volts

So for simplicity's sake, let's take a 9006 low beam bulb rated 1000
lumens at 12.8 Volts (the H4 low beam has the same rating) and plug in different voltages:

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

Now, in the case of overwattage bulbs (100/90 and so forth), things are
different, you likely WILL burn up your car (or at least parts of it)
unless you upgrade the wiring.

So, to sum up:

Relays are a good idea with stock wattage; they are mandatory with
overwattage.

As far as pictures of the different beams, beam diagrams are much better. Photographs of light are easy to manipulate to "show" whatever you want shown, because digital and film cameras don't work the same way as the human eye.

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.

Here's a beam diagram of the US sealed beam (low beam) you're starting with, projected down the road:
http://dastern.torque.net/Photometry/2C1_L.jpg


The beam is narrow, "tunnel" shaped, puts very little light on the road surface, and has a great deal of upward light which makes overhead road signs blaze, but which also causes backdazzle in bad weather and glare. About the only good thing about this beam is that the high-intensity "hot spot" is fairly bright for good down-the-road seeing distance.

Now, here's a beam diagram of the common Hella E-code lamp:
http://dastern.torque.net/Photometry/Hella_7_Iso.jpg

Beam is wider and better focused, and there's much less upward stray light. But, it's still not really wide, and there's not a whole lot of light in the beam overall (just 463 lumens, which is pathetic)

Now, here's a beam diagram of the Cibie E-code lamp:
http://dastern.torque.net/Photometry/Cibie_7_Iso.jpg

MUCH wider, much more light within the beam (695 lumens).

I don't have a Bosch diagram, but they make an excellent large rectangular H4 lamp, just about identical in performance to the Cibie.

The idea to get across here is that you have to pick your conversion lamps carefully. They are not all equal. It's not enough just to get any ol' H4 light that fits your car; as you can see, even among major-brand lamps there are significant performance differences.


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