Light mounting height and apparent intensity

In article said:

Has anybody written anything up that quantifies the apparent
difference in intensity between a light mounted at wheel height vs.
handlebar height? Links? I've noticed a fairly significant
difference, with the handlebar mounting appearing much brighter,
which is unfortunate because I really do prefer my lights mounted
down low for uncluttered handlebars.

The idealized math is pretty simple, 1/r^2. This ignores issues of
reflectance versus absorption of light by pavement, issues of diffuse
reflection versus specular reflection, etc., but gets the job done in a
simple and easily understood manner.

http://imagine.gsfc.nasa.gov/YBA/M31-velocity/1overR2-more.html

Lower mounted lamps will create a smaller but brighter pool of light on
the pavement. Of greater benefit, IMHO, is that the light beam from the
lamp is more parallel to the road surface and thus reveals surface
irregularities by exaggerated shadowing. And the pool of light tends to
be longer as well. Mounting lights up high tends to lead to
ever-increasing wattages for lamps to try to overcome the inverse square
law.

Rex Kerr said:

Has anybody written anything up that quantifies the apparent difference
in intensity between a light mounted at wheel height vs. handlebar
height? Links? I've noticed a fairly significant difference, with the
handlebar mounting appearing much brighter, which is unfortunate because
I really do prefer my lights mounted down low for uncluttered handlebars.

Given that road conditions (both traffic and road surface), ambient
light, bike speed and rider expectations vary quite a bit, I'd just tape
it on high and then low on successive trips.
You may have no preference at all or you may find one position better
for you and your route.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Tim McNamara said:

Lower mounted lamps will create a smaller but brighter pool of light on
the pavement.

That's not necessarily true! If the downward tilt angle of the lamp
is held constant, what you say will be true, and the pool of light
will be closer to the bike as well; but there's no reason to hold that
angle constant. The normal thing to do would be to lessen the
downward tilt for a lower-mounted lamp, so the pool of light is
approximately the same distance in front of the bike.

Quoted message said:

Of greater benefit, IMHO, is that the light beam from the
lamp is more parallel to the road surface and thus reveals surface
irregularities by exaggerated shadowing. And the pool of light tends to
be longer as well.

I agree.

One downside to mounting extra-low is that the result is more
sensitive to angles - both the tilt angle of the lamp, and the angle
of the road with respect to the bike. For example, cresting a hill, a
too-low lamp may shine off into space, rather than illuminate the road
surface. I learned this with one of my small wheeled bikes, whose
headlight is only about a foot off the ground.

For me, the optimum height seems to be about 24" to 27" above the
road. That seems to give a nice view of road "relief" or roughness,
yet not be too sensitive to angle changes. And it's especially nice
to have the light on the leading edge of a front rack.

Quoted message said:

Mounting lights up high tends to lead to
ever-increasing wattages for lamps to try to overcome the inverse square
law.

Good point.

- Frank Krygowski

Quoted message said:

For me, the optimum height seems to be about 24" to 27" above the
road.  That seems to give a nice view of road "relief" or roughness,
yet not be too sensitive to angle changes.  And it's especially nice
to have the light on the  leading edge of a front rack.

Yup. Got my front light JB welded under the front rack. Looks sharp,
is out of the way, and as it's an urban be-seen light, it puts the
light around where it would be on a motorbike, which has a good
psychological affect on motorists (I think).

http://farm3.static.flickr.com/2201/2105535405_afda203cd5_b.jpg

aka Frank Krygowski said:

Tim McNamara said:

Lower mounted lamps will create a smaller but brighter pool of light on
the pavement.

That's not necessarily true! If the downward tilt angle of the lamp
is held constant, what you say will be true, and the pool of light
will be closer to the bike as well; but there's no reason to hold that
angle constant. The normal thing to do would be to lessen the
downward tilt for a lower-mounted lamp, so the pool of light is
approximately the same distance in front of the bike.

Quoted message said:

Of greater benefit, IMHO, is that the light beam from the
lamp is more parallel to the road surface and thus reveals surface
irregularities by exaggerated shadowing. And the pool of light tends to
be longer as well.

I agree.

One downside to mounting extra-low is that the result is more
sensitive to angles - both the tilt angle of the lamp, and the angle
of the road with respect to the bike. For example, cresting a hill, a
too-low lamp may shine off into space, rather than illuminate the road
surface. I learned this with one of my small wheeled bikes, whose
headlight is only about a foot off the ground.

For me, the optimum height seems to be about 24" to 27" above the
road. That seems to give a nice view of road "relief" or roughness,
yet not be too sensitive to angle changes. And it's especially nice
to have the light on the leading edge of a front rack.[...]

Hey, that is about handlebar height on my bicycle!

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

Rex Kerr said:

Has anybody written anything up that quantifies the apparent difference
in intensity between a light mounted at wheel height vs. handlebar
height? Links? I've noticed a fairly significant difference, with the
handlebar mounting appearing much brighter, which is unfortunate because
I really do prefer my lights mounted down low for uncluttered handlebars.

If you're using a 3W dynamo light, keep it down low. If you're using a
high-power lighting system, keep the lights on the bars.

Usually lower power lights are mounted lower, as the primary goal is to
use the limited amount of light to illuminate the pavement directly in
front of the bicycle. Higher power lights illuminate further ahead, as
well as to the sides.

As Marty Goodman wrote, ""With vastly more light available, night
bicycling is qualitatively far safer. The road can be lit both further
ahead and, even more important, far more brightly to the sides of the
bicycle."

Quoted message said:

For me, the optimum height seems to be about 24" to 27" above the
road. That seems to give a nice view of road "relief" or roughness,
yet not be too sensitive to angle changes. And it's especially nice
to have the light on the leading edge of a front rack.

Quoted message said:

Mounting lights up high tends to lead to
ever-increasing wattages for lamps to try to overcome the inverse square
law.

Good point.

- Frank Krygowski

The distance is probably not a factor. Assuming, for example, that the
center of the beam is 20' from the light, a height of 12" vs. a height of
36" ('way more than I'd expect in reality) results in an intensity difference
(using the square relation of distance to intensity) of less than 2%.

What might be a tiny bit more significant is that the steeper angle of
the higher light source will result in a smaller "patch" of light - with
the light being more intense within the patch.

[I still like the lower lamp mount point for the improved shadows!]

-f

In article <[email hidden]>,

Tim McNamara said:

In article said:

Has anybody written anything up that quantifies the apparent
difference in intensity between a light mounted at wheel height vs.
handlebar height? Links? I've noticed a fairly significant
difference, with the handlebar mounting appearing much brighter,
which is unfortunate because I really do prefer my lights mounted
down low for uncluttered handlebars.

The idealized math is pretty simple, 1/r^2. This ignores issues of
reflectance versus absorption of light by pavement, issues of diffuse
reflection versus specular reflection, etc., but gets the job done in a
simple and easily understood manner.

http://imagine.gsfc.nasa.gov/YBA/M31-velocity/1overR2-more.html

Lower mounted lamps will create a smaller but brighter pool of light on
the pavement. Of greater benefit, IMHO, is that the light beam from the
lamp is more parallel to the road surface and thus reveals surface
irregularities by exaggerated shadowing. And the pool of light tends to
be longer as well. Mounting lights up high tends to lead to
ever-increasing wattages for lamps to try to overcome the inverse square
law.

Best to keep light 20-40 degrees off the visual axis.
Less specular reflection into the eyes, better relief.

--
Michael Press

In article <[email hidden]>,

Tom Sherman said:

Hey, that is about handlebar height on my bicycle!

!

--
Michael Press

Yup. Got my front light JB welded under the front rack. Looks sharp,
is out of the way, and as it's an urban be-seen light, it puts the
light around where it would be on a motorbike, which has a good
psychological affect on motorists (I think).

It seems to me that it would be better to have two lights there, so as to
make the observer wonder if you were riding a much large bike. At the very
least, they would be alert to your bike and not just think "Oh, a little
bicycle."

Pat said:

Yup. Got my front light JB welded under the front rack. Looks sharp,
is out of the way, and as it's an urban be-seen light, it puts the
light around where it would be on a motorbike, which has a good
psychological affect on motorists (I think).

It seems to me that it would be better to have two lights there, so as to
make the observer wonder if you were riding a much large bike. At the very
least, they would be alert to your bike and not just think "Oh, a little
bicycle."

Not long after I built my twin 5 watt Luxeon bike lights a friend told
me he was waiting at an intersection for a "very slow motorbike" to pass
through. Which was me of course.

Elm

Tom Sherman said:

Quoted message said:

Quoted message said:

How about fork mounted, handlebar mounted and head mounted lights?

Quoted message said:

I was suggesting all three positions in combination.

Isn't one of them (the first one if you ask me, the other two I do use
myself as well) rather redundant?

A R:nen said:

Tom Sherman said:

Quoted message said:

> How about fork mounted, handlebar mounted and head mounted lights?

Quoted message said:

I was suggesting all three positions in combination.

Isn't one of them (the first one if you ask me, the other two I do use
myself as well) rather redundant?

Exactly!

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful