In a dystopian future, a cross country automobile race requires contestants to run down innocent pedestrians to gain points that are tallied based on each kill's brutality.
For those of you have read my previous articles, you’ll know I am great fan of these genre of films- mainly for the shoot them up and kill aspect rather than any moralistic pespective on possible futures.
The distopian future written about Ib Melchior in 1975 was set in 2000. Looking back to the then future, how wrong was Ib in reality?
Our roads continue to be a hazard of our own making. We may not deliberately go our of way to ‘mow’ people down, but the system and especally lighting we put up, play a contributory factor in many of the accidents we face here and world wide.
So hands up who’s been in crash?
So if you’ve never been in an accident. Count yourself lucky.
But for those who have, and need to fill a report you’ll notice that on this form, you need to fill in spaces relating to day/night. Whether the collision occurred in the day or at night.
You will also see that, if your collision happened at night, there is a space for “Lit by street lights.”
In layman’s terms it couldn’t be simpler. Was it dark or was there light. Could you see or could you not!
But is it really this simple? Can you truly make a determination as to whether someone could see - TRULY SEE - simply by whether there were lights, or not?
The truth is no - it is actually much more complicated than this. There are human (lighting engineering) factors that stretch far beyond the lay understanding of lighting.
This is a lay description of how lighting is interpreted for the purpose of collision analysis involving lighting as an actual or possible factor.
But let’s break it down into its components parts first:
Pupil Dilation, Age, visual acuity and Eye Colour
What you see is the result of light striking the inside of your eye through what appears to be the black hole you see when you look in a mirror – the light enters through your pupil and an image is formed by a clear lens onto the retina (which is black because it is highly non reflective).
This little hole (pupil) is not constant and can vary in size. Even more importantly the Left and Right pupils can dilate at differing rates and to different diameters.
You can do a test to see this. Stand in front of a mirror, then close one eye for about 30 seconds and remove your hand then look in the mirror. You will see that the pupil dilation will be different for each eye.
The way in which this works is that less light results in your pupil dilating more to let in more light.
At the same time, if you experience bright light, your pupils will contract and thus prevent too much light entering the eye.
This automated system is constantly trying to balance the amount of light entering the eye in relation to the intensity of the light to enable you to see perfectly under varying conditions.
The problem is that this same system can conspire to render you vulnerable at night as you get older. In the average (healthy) person, the pupil can dilate or contract in a second or two.
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If an approaching vehicle’s lights then shine into your eyes at night, your eyes will adjust and contract your pupils, cutting out some of the glare and making it possible for you to see better.
But as you get older, this reaction slows down to as much as 10 or 15 seconds, depending on the full effect of ageing (and a variety of physiological factors).
This means that - as the vehicle now approached with its lights on, your pupils will not contract quickly enough.
This results in over-exposure and you are thus “temporarily blinded” by the approaching vehicle.
This leaves an after-effect (light spots) rendering your vision impaired while your eyes and visual system attempts to cope with this over-exposure.
After this, the other car passes but your pupils are still dilating. Now those lights go away and your pupils need to dilate again to allow in more light to allow you to see under the lower lighting.
Again - because of the slower reaction of the pupil, you would now be “night-blind” for up to 15 seconds as your aged pupils dilate slowly again.
In total, this effect could influence your ability to see properly for as long as 30 seconds or more.
If a pedestrian stepped out, if a vehicle stopped ahead of you or if there is a bend in the road, you could be in grave danger.
But this deterioration in your visual system happens so gradually and over so many years that you would probably not even be aware that this is happening until you think hard, after reading this.
So, the question “Was there street lights” should be linked to and followed by “how old was the driver” and “under what lighting conditions and with what kind of momentary exposure - as experienced by the driver - did the collision occur.”
In spite of this, your eye will also experience a reduction in light sensitivity over time.
Like an old tube television set, you “need to turn up the dials more and more to see the same quality picture.”
This reduction in visual acuity affects us also as a function of natural ageing.
As your slower-reacting pupils and less sensitive visual perception (light sensitivity) conspire, you will start to experience acute night blindness. You will start to notice that driving at night becomes onerous and even uncomfortable.
By the time you need to blink lots of times after an approaching vehicle has passed, the effects will have started and you should be aware of this.
Lighting Types
Are all street lights created equal?
Remember that the Accident Report (AR) Form only had an option for “lit by street lights.” There is no reference to any consideration for the TYPE of lighting installed on a particular piece of road.
In layman’s terms, you would imagine that lights there is better than no lights there, right? Well - not really, in all cases.
To determine if the mere presence of light is all that needs to be pondered, we need to consider a variety of lighting principles that affect this concept.
We’ll start with Sunlight.
Sunlight (as we are all surely aware) can be described as “optimal.” We are “built” to see under ideal (sunlight) conditions. In order for us to truly consider the “quality” of street lights, we need to understand why sunlight is so “good” to us.
First, there is the issue of the wavelengths of visible light. We can see only a specific part of available light, the bit between Ultra Violet and Infra Red called visible light.
Ultra Violet is closer to the "radio-active" frequency range, such as X-rays and gamma rays and Infrared closer to the “heat” range and microwave range.
We can only see the light that falls between these extremes. Everything outside of our limited field of colour detection is invisible to us.
On the one side we have light beyond blue (Ultra Violet) and on the other end the light beyond red (Infra-red) that we cannot see anymore. We only see the lights at the wavelengths (colours) in between - this is visible light.
If you look at the chart on this page, you will see that it indicates our sensitivity to lights in daylight at varying wavelengths – the so called photopic response curve. We experience greens with most efficiency and red and blues less so tailing off markedly into ultra violet and deep red.
Scotopic/Photopic or S/P Ratio
Now we have to get a bit technical, but bear with us. This is important stuff.
Inside your eye there are two different kinds of sensors. One type (rods) only has one colour type centred in the blue-green region and another kind (cones) sense colours in the Red, Green and Blue spectrum. See picture.
The rods outnumber the cones by roughly 2.5 to 1. However, the distribution of rods and cones in the eye are quite distinct with cones mainly clustered in the sharp vision part of the eye called the fovea.
As the light level drops the cones become less active and rods take over the visual process as shown below
This is very significant and explains why we tend to see in muted colours or in mere outlines as lighting intensity drops.
In darkness, it is almost like seeing only shadows, but you will see that - in very dark conditions - you can actually “see” a bit better in the periphery of your vision due to the large number of rods outside of the centre of the fovea.
You can try this on a very dark night, looking a single light source, like a very small star.
If you look straight at it, it seems to be invisible, but when you look to the side, it becomes more visible.
The rods and cones have different response curves leading to different sensitivities over the wavelength range. During daylight conditions the cones dominate and the photopic response curve dictates our colour sensitivity. However, at night when the rods take over we have a different response function as shown below.
As can be seen the scotopic response is much more efficient than the photopic as the rods are much more sensitive but at lower light levels. Also, we see that at night the peak of the response shifts to the blue part of the wavelength range.
For a given wavelength spectrum of a light source one can define the scotopic/photopic (S/P) ratio of the light source which indicates how much of the light is contained within the wavelength regions which are concerned with scotopic or photopic vision. This means it can provide an estimation of how good the light source will be for night time vision compared to day time vision.
A selection of these S/P ratios for typical light sources is shown below.
Looking at the above chart, you will see that Sodium lights have the poorest S/P Ratio of all artificial light types. This is due to fact that they have a predominantly orange colour and when the rods take over they are very inefficient in the orange part of the wavelength spectrum.
You will see that the S/P Ratio of the sun is (roughly) 2.5.
Or almost exactly equal to the ratio between rods and cones in your eye.
As this ratio drops, you need more and more rods to see properly - but this is a double-edged sword.
A light of poor S/P Ratio will result in your eye “seeing” more light but of the WRONG colour.
This results in your pupils trying to dilate (since the cones are not being stimulated adequately) and this further “over-exposes” the rods.
If you stand in a shipyard, between containers, where there are HPS lamps installed, you will see that you see poorly (at best) in lit areas while the shadows now seem EXTREMELY dark.
You could stand two feet from someone in a brightly lit area and not see them standing in a shadow almost right next to you.
You can see from this chart that the light distribution is very narrow for HPS lamps. This means you are getting lots of light, but “seeing less."
This is because your eyes are over-exposed and under-exposed at the same time. The rods are reacting brilliantly but the cones are “confused.”
Another problem with HPS and other types of fluorescent lights is….
Flicker
You may not be able to sense it, but most Fluorescent and Discharge lamps are actually flickering at a high frequency.
While you may not be able to see this, your eyes will fatigue quickly, this flicker can cause concentration, focus and even balance impairment.
Since we know that people can suffer from epileptic fits from flicker, this is a risk that needs to be considered when installing lighting where vehicles move at over 100 Km/h.
It is also known that this flicker effect can be experienced by some drivers where the sun flashes in-between trees on a country road.
So - why do developers keep planting rows of trees along highways? Because they look pretty, of course! This effect can add another dimension, called…
Stroboscopic Effect
The place where you will easily see this is when you watch a vehicle wheel with spokes that is turning.
The same is true for aircraft propellers.
At some point the wheel will tend to slow down and stop and then it starts seemingly turning in the opposite direction.
This means that - in factories where there are loud machines - workers might have no auditory cue as to which machines are operational (turning) and which are not.
The presence of the stroboscopic effect here can then lead to a worker placing his hands on a machine that SEEMS to be standing still when in fact it is not.
This can also influence drivers, but to a lesser effect.
Drivers may also be affected by stroboscopic effect due to the change in the perception of speed of travel associated with this effect.
So the combination of everything just mentioned and the “strain” this can place on the visual system is measured as…
Visual Comfort Of Perception (VCP)
VCP is a number that expresses the relative “comfort” with which concentration and attention span can be used to optimum effect for the longest time, without causing fatigue, disinterest, failure to concentrate and/or a decrease in judgement.