Headlight Illumination & Outdriving Them

[jaudette3]

The discussion in another thread where I have posted some H1's for sale has made me curious about headlights and their capabilities and limitations and I've started to do a bit of research.

According to one source, the Roadtrip America website, the average high beam headlight range is about 350 feet and on low beam the average distance that a headlight can reach is about 160 feet.

Which according to the following means it's pretty easy to outdrive your headlights according to this analysis taken from http://www.visualexpert.com/Resources/reactiontime.html :

Here's a simple example. Suppose a person is driving a car at 55 mph (80.67 feet/sec) during the day on a dry, level road. He sees a pedestrian and applies the brakes. What is the shortest stopping distance that can reasonably be expected? Total stopping distance consists of three components:

1. Reaction Distance. First. Suppose the reaction time is 1.5 seconds. This means that the car will travel 1.5 x80.67 or 120.9 feet before the brakes are even applied.

2. Brake Engagement Distance. Most reaction time studies consider the response completed at the moment the foot touches the brake pedal. However, brakes do not engage instantaneously. There is an additional time required for the pedal to depress and for the brakes to engage. This is variable and difficult to summarize in a single number because it depends on urgency and braking style. In an emergency, a reasonable estimate is .3 second, adding another 24.2 feet.

3. Physical Force Distance. Once the brakes engage, the stopping distance is determined by physical forces (D=S²/(30*f) where S is mph) as 134.4 feet.

Total Stopping Distance = 120.9 ft + 24.2 ft + 134.4 ft = 279.5 ft

Notice that stopping distance increases rapidly depending on speed, as mph is squared in the formula.

A lot of variables here, such as reaction time, weight of the car, quality of tires and brakes, etc., but it appears to be pretty easy to outdrive the headlights ability to illuminate. It'd be great to have input from some of the engineers and technical types here.

John

[Mr9146]

That's what "driving lights" are for...right?

[jaudette3]

Any data on the range of driving lights?

John

[Harvey Weidman]

I commuted in my Porsche many miles (50k+mi) at night with H-4s and their distance is way more than 160 or 350 ft. I would guess more than 600 ft?
I remember the Super Oscar advertising their range to be over 1/4 mile.
There are some detailed studies. I remember seeing the comparison of all the lights somewhere.
H

[jaudette3]

I'm going to look for data on the range of different lights. I'm interested in H1's, H4's, H5's and driving lights. I'll post it here when I find it. Off to honor some Marines the rest of today.

John

[Fishcop]

I retired my RHD H1s a few years ago and replaced them with H4s. John, I've been watching your H1 restoration projects with the intention of doing the same with mine at some time.

I know my H1s had certainly lost a lot of their efficiency, but I was astounded at how good H4s were once 'specced up' to 60/120 globes and running relays direct to battery. And then I added a pair of cibies I actually prefer the set up to my current daily driver's zenons.

I tend to agree with Harvey that they are good for more than 500 feet. We have giant grass-hoppers (kangaroos) and walking menheirs (wombats) over here that will destroy a car if hit at the speed limit (60mph). I've had a few close calls, but they were mainly due to my average reaction times and a kangaroo's tendency to hop AT the lights! Thanks to the light set up I certainly saw them coming though

[RickS]

I put fused, relayed 80/120s in my H4s and over driving them was never an issue. With the beam cut-offs, no one has ever flashed that the lows were too bright.

Also replaced the through the grill fogs with H3 drivers and now the night almost turns into day.

[68911+1]

+1 on installing fuse and relays (2). Made all the difference in my '68 with H4's.

[rpidduck]

My car has had both H1 (original) and H3 118 driving lights TTG mounted. In the old days with US headlight specs, the H1s were a decided asset. But with the power of today's H4 headlight conversion, they become slightly superfluous. However, I love the period look and will keep them forever.
-Richard