Many international studies have been conducted on the detectability or probability of vision, expressed as the percentage of objects located at different points on a road with a given illumination that can be perceived by the human eye.  (These objects had the common reflectance of the clothing of a pedestrian that could be distinguished by the observers).

These studies concluded that detection performance depends on three factors: the average luminance of the road, the overall uniformity of that luminance and the level of disability glare or increase in the threshold increment (TI).

The results show that for a luminance of 1.5 cd/m2, a low level of overall uniformity of Uo = 0.2 reduces the probability of vision  by up to 42% compared to a level of overall uniformity of Uo = 0.4. At higher luminance levels, the probability of vision is less pronounced, with ranges between 5 and 15%.

It is important to note that uniformity is a critical factor at low luminance levels (such as those found in tunnels or when emergency lighting is switched on after a power failure).

The IOHNIC solution provides 100% uniformity compared to conventional tunnel lighting solutions, where the light points are distributed separately and are less uniform.

When emergency lighting is activated (with a lower luminous flux), IOHNIC keeps all the light points on, which keeps longitudinal uniformity close to 100% at critical luminance levels. Conventional solutions, on the other hand, use other methods; they usually switch off luminaires to reduce luminous flux, which decreases uniformity and reduces the probability of vision.

IOHNIC’s uniformity prevents the flickering effect caused by the distance between the luminaires and the speed of the vehicle. 
 

It has been scientifically proven that reducing the TI glare index improves visual perception. Reducing TI glare from 30% to 7% at luminance levels of around 1 cd/m2 increases the probability of seeing an obstacle by 33%. These lower luminance levels correspond to typical tunnel conditions. Similarly, when IT glare is reduced from 30% to 7% at luminance levels above 2 cd/m2, the probability of seeing an object increases by 12%.

Glare causes the pupil to contract, blocking light from entering the eye, which reduces visual sensitivity and causes discomfort. In conventional tunnels with an unobtrusive light source, the pupil reacts as follows:

Unlike discrete solutions, in which open optics create an effect of light-darkness on the road, IOHNIC eliminates the disability glare TI thanks to its closed optics, which is only possible with a continuous arrangement of luminaires. As shown below, the light beams of the IOHNIC luminaires interface with the driver at an angle of less than 30° so they do not cause glare. This is an important difference with respect to the solutions with conventional open optics, whose angle of incidence is greater 40° and that cause glare as a result.

In other words, inside the ‘glare zone’, the light beams do not reach the driver’s eyes, which means that IOHNIC can eliminate the uncomfortable TI glare.

This enables drivers to predict the trajectory inside the tunnel by means of lateral lights, which help the driver to position the vehicle in conditions of poor visibility. This type of lighting is used on roads that cannot be adequately lit, as in the case of airport runways at night.

Backlight has two key advantages:

1) It improves the contrast of objects on the road. This contrast is dark against a light background: the darkness of the object is created by the glare and shadow of the backlighting on the obstacles, while the light background is created by improving the reflectivity of the road surface.

2) It improves the reflectivity on the road by increasing luminance for the same power, resulting in a lower power consumption.  

Luminance levels are adjusted to the levels required by the International Commission on Illumination (CIE), combining the highest standards of safety and precision. This means that the lighting level is adjusted gradually and continuously, with no jumps.

The graph shows how the lighting power (blue) in the IOHNIC solution precisely matches the power required by the CIE (orange), while the conventional solutions (green steps) are much less precise.

Tunnel lighting regulations specify luminance levels at the tunnel entrance that are proportional to the luminance of the tunnel entrance during the day. Generally, three regimes are implemented: sunny, overcast and twilight. When the day begins to lighten, twilight mode is activated, and when the outdoor luminance reaches a value higher than the value set in the twilight mode, the system switches to overcast mode. This ensures the proper luminance level from dusk to dawn. With IOHNIC, we achieve a much more precise adjustment of energy consumption because the power of the auxiliary lighting at the entrances is adapted to the external lighting conditions in real time.

The following graph shows the power consumption of a conventional system in grey and the consumption of the IOHNIC system in blue. 

The figure below shows the adjustment of the IOHNIC system: 

The real-time power adjustment can vary with the outdoor luminance, but it can also be adapted to the traffic characteristics, so that the flux decreases along with the intensity of the traffic. IOHNIC is on the cutting edge in this regard, because the adjustment of flux based on traffic levels has not yet been included in national regulations.

Lighting efficiency has a direct impact on energy consumption and therefore on CO2 emissions. The IOHNIC solution uses Nichia LEDs, which have a very high flux density and achieve efficiencies of more than 200 lm/w when powered at low current. In the case of IOHNIC, taking into account losses due to the driver, optics and protective glass, among other aspects, we obtain an overall lighting efficiency of around 150 lm/w, compared to 130 lm/w for conventional solutions.

The life span of the luminaire refers to the life span of the driver and the LED modules. In general, the driver is the most critical element because it contains electrolytic capacitors. The life span of the driver is more than 120,000 hours.

The life span of the LED modules is longer. Using the life span value from the L80 test (10K), and assuming current and temperature variable values of 100mA and 85°C respectively, a value of 144,000 hours is obtained. This value indicates that, after 144,000 hours, only 20% of the light output has been affected.

IOHNIC can be connected to the uninterruptible power supply (UPS) of the permanent circuit in the event of a power failure. This allows all the luminaires to remain in operation and maintain uniformity, which is very important in cases of poor visibility. This means that two luminaires can be installed in one, combining backup and permanent lighting while keeping them electrically independent. The result is a reduction in manufacturing and installation costs and an improvement in the linearity and visual appearance of the tunnels.

The extra power of the driver makes it possible to compensate for the loss of LED flux due to wear and dirt each year, and also to reinforce areas compromised by accidents, obstacles or maintenance work. The additional power also reduces the frequency of cleaning by compensating for the loss of flux with an increase in luminous load.

IOHNIC includes more than 500 luminaires with different wattages and configurations to meet the precise lighting requirements at each point of the tunnel, and to adapt to all circumstances. The wattages range from 6 watts to 1,283 watts per metre of tunnel, providing fine scaling that enables us to adapt to the specific power requirements of each project. This adjustment ensures that the drivers operate in optimum conditions, reducing their harmonic distortion and maintaining high efficiency and power factor levels.

The independent functioning of the LED module and the driver allows for easy maintenance. With this system, damaged components can be easily replaced using IP threaded connectors, so if a driver is damaged, only the individual driver needs to be replaced, not the entire luminaire. Similarly, if a module needs to be replaced, only that module, and not all the modules that make up the luminaire and, of course, not the driver, is replaced. This increases the life span of the luminaires because in the event of a replacement, only the affected product is switched out. This increases the useful life of the luminaires and reduces the waste that is generated.

The versatility of the LED modules and drivers to create different luminaires minimises the need to stock components for each tunnel.

IOHNIC lighting is designed specifically for tunnels. One of the specific characteristics calculated for each tunnel is the angle of projection of the light beam. This is very important because the lens used in the IOHNIC system is designed to direct the light exactly where it is needed, so the optimum angle will vary depending on the dimensions, shape, and location of the luminaire inside the tunnel.

The IOHNIC system's LED modules and anchors allow the angle to be adjusted to the correct position. Also, the same anchor system is used between adjacent modules for perfect alignment.

The innovative design of the extruded profile with internal fins increases the convective surface area and reduces dirt build-up, which improves heat dissipation and results in a longer useful life.

Adjusting the colour temperature to cooler tones in the tunnel interior improves visibility in low light conditions and increases the viewing angle and depth of field.

Photopic or daylight vision is provided by the cones, whose sensitivity is only 683 lumens per watt of light radiation. The field of vision is also very narrow because the cones are located in the central part of the fovea.

The cones are most sensitive to warm colours, with wavelengths around 555nm. This is the range of the sodium vapour, whose light is optimal for high lighting levels.

On the other hand, scotopic or night vision is provided by the rods, which are much more sensitive to cold light (1700 lm/w). In addition, their field of vision is very wide, since they are located outside the central zone or fovea, although they present lower sharpness.

Inside the tunnel, where luminance is between 2 and 6 cd/m2, the eye works in mesopic vision, which means that scotopic vision and photopic vision are used at the same time, with cones and rods working simultaneously. Lighting a tunnel with cold light and with wavelengths close to 500 nm makes the rods work better, improving the sensitivity and the angle of vision.

Cold light has also been shown to facilitate pupil constriction, which helps to see detail and depth of field.

The wavelength of sodium vapour lamps at low light levels cannot be used by the rods so visibility is reduced. To address this, the IOHNIC system includes the following features: 

• A lighting temperature of 4000K in the reinforcement zone during the day, (tunnel entrance). High luminance levels.

• A lighting temperature of 5000K for the permanent lighting, (tunnel interior). Very low luminance levels. 

Under these conditions, visual perception is three times higher than in tunnels lit with VSAP. The amount of light perceived by the human eye, taking into account what is captured by the rods, is called pupil lumen "pLm". In the case of VSAP, pLm = Lm * 0.65. With IOHNIC, pLm = Lm * 2.15. The factor applied to the measured lumens is called the S/P ratio. This means that the vision in inside tunnels with IOHNIC lighting would be: 

Polycarbonate lenses

Most luminaire manufacturers choose PMMA (polymethyl methacrylate) for their lenses. This is because PMMA is more transparent, affordable and resistant to UV light than PC (polycarbonate). However, PC is much harder and more stable than PMMA. At IOHNIC, we apply additives to the PC to mitigate the effects of UV light and increase the efficiency of the luminaire to compensate for losses caused by the lower transparency, resulting in a much more durable lens that will not yellow with age over the years.

Fog behaviour 

In fog conditions, it is essential to focus the light and mark the limits of the road. For this reason, IOHNIC uses tightly closed lenses whose light beams present minimal diffraction when they come into contact with the fog. Conventional systems, on the other hand, use open optics that produce an "explosion" of light in contact with the fog, creating volumetric glare and causing a blinding effect and lack of visibility on the road.

Another aspect is guidance. In conditions of poor visibility, it is important for the driver to know where the limits of the road are at all times. In this respect, IOHNIC, as a linear and continuous solution installed on both sidewalls at lower heights than conventional systems, provides guidance.
For all these reasons, IOHNIC is the safest solution on the market in fog.