Learning Center
Plans & pricing Sign in
Sign Out



Lighting power controllers

                                         RNIG02E2 – rev.2 – 0206

                             Via Artigianale Croce, 13
                             42035 Castelnovo ne’ Monti (RE)
                             Tel. +39 0522 610 611
                             Fax. +39 0522 810 813


1. PREAMBLE                                                            4

2. ROAD TUNNEL LIGHTING STANDARDS                                      4

3. THE TERMINOLOGY                                                     4

4. THE FOCAL POINTS OF THE PROBLEM                                     4

5. THE VISUAL TASK                                                     5

REINFORCEMENT ZONES                                                    8

7. THE PERMANENT LIGHTING CIRCUITS                                    10

8. THE EMERGENCY LIGHTING CIRCUITS                                    12

9. CONCLUSIONS                                                       12

APPENDIX“A” TERMINOLOGY                                              13

Power controllers – rev. 2                                  Pag. 3 of 14
                                                                        ROAD TUNNEL LIGHTING

The lighting of road tunnels is aimed at assuring traffic safety, a not easy task. The car drivers
arrive from the external environment with a natural lighting level which can be very high, even
over 100000 lx horizontally. Consequently, they look at a tunnel like at a black hole in which they
are supposed to perceive the presence of dangerous situations, like obstacles, queues or traffic
stops. Not to say about the luminance of the exterior environment around the tunnel opening
(like the summer sky or the daylight reflected by the snow) which create a form of glaring which
reduces the visibility.

In order to minimise installation and energy costs for tunnel lighting, norms foresee to correlate
road luminance with actual external lighting and traffic flow. These are conditions where the use
of the regulators of luminous flux show very interesting aspects from the points of view of both
the lighting applications and more generally of the economic implications.

In the present document the problem of setting the lighting level in road tunnels is described with
particular attention on both technologies of the regulators designed and manufactured by
Reverberi Enetec srl, without any attempt to give a complete picture of their performances, which
are described in the general catalogue of Reverberi Enetec srl.

After the known accident in the Mount Blanc tunnel, the Italian Ministry of Public Works issued a
circular, published on Gazzetta Ufficiale of 18 September 2001, which requests the compliance
with the publication CIE 88/90 “Guide to the lighting of road tunnels and underpasses” and
foresees a tight updating programme for the existing lighting installations. The character of CIE
88/90, which was prepared and issued under urgent pressures, is mostly empirical and leads to
conservative and expensive prescriptions, very often disregarded by road and highway
administrators. Actually, both new and updated tunnel lighting installations complying with CIE
88/90 involve either investments and maintenance costs much higher than necessary. This is
why CIE will soon publish an updated version of CIE 88/90 based on scientific foundations,
which assures even higher safety levels in tunnels with less expensive prescriptions.

Based on the same principles, UNI issued the norm 11095 “Lighting of tunnels” (2003), under
acceptance by the Ministry of Infrastructures and Transportations, similar to the updated CIE 88
but for some luminance levels, which have no influence on the use of luminous flux regulators.

The lighting terms used in the present document are defined at appendix A.

The situation of road tunnels in Italy is clarified in the draft directive or the European Parliament
2002/0309 of the safety of traffic in the tunnels longer than 500 m existing in the Trans European
Network (TEN), which includes only a minority of the Italian highways.

Pag. 4 of 14                                                               Power controllers – rev. 2

                                 Table 1 - Tunnels in the highways
                                   TEN, Trans European Network
                                            March 2002
                                                   > 1000 m      > 500 m
                       Austria                           33          64
                       Belgium                            1            2
                       Demmark                            1            3
                       Finland                            0            5
                       France                            18          35
                       Germany                           19          55
                       Great Britain                      6          12
                       Greece                             3          45
                       Ireland                            0            1
                       Luxemburg                          0            3
                       The Netherlands                    1          11
                       Portugal                           1            2
                       Spain                             16          25
                       Sweden                             0            3
                                   UE minus Italy       99            266
                       Italy                            83             246

                               Total UE Countries      182            512

The number of TEN tunnels in Italy is almost equal to that of all the other UE countries together.
Even if no analysis of the Italian road and highways tunnels is known, their number is estimated
to be higher that 2000. Add to that that the Italian tunnels cross mountains, while in some flat
countries there are only some underpasses and artificial tunnels and lighting does not involve
big economic problems.

Taking account of what said at point 2, it can be easily understood that in the next years the
lighting installations of many tunnels will be updated according to the norm, not to say about the
new tunnels as the ones foreseen in the new highway between Bologna and Florence. The
consequence will be an increase of the requests of luminous flux regulators suitable for such
types of installations.

Even if the aim of this document is not the lighting design, it is convenient to summarise the
content of the norm for the sake of better understanding the advantages implied in the
application of the luminous flux regulators in road tunnel lighting installations.

Both CIE and UNI identify the safety conditions in the entrance zone of a tunnel with the visibility
of a reference obstacle, actually a cube with 20 cm edges and diffusing faces with a reflection
factor of 0,10: it is a very dark object, which is considered to represent the smallest potentially
dangerous obstacle which could be found on our roads.

 Power controllers – rev. 2                                                            Pag. 5 of 14
                                                                                                                ROAD TUNNEL LIGHTING

In particular, if such type of object was present on the road in the entrance section of a tunnel, an
accident could be avoided only if the driver could perceive it at the stopping distance from the
said section, in order to permit to stop the vehicle in due time.

As sown in figure 1, the actual stopping distance is much higher than what reported in the
journals specialised in the automobile sector: actually, not only real tyres and roads are almost
never in ideal conditions, but account should be taken of the reaction time of the average driver,
which the norms assume equal to 1,5 seconds.


                              Stopping distance [m]

                                                                                             ad             d
                                                                                           ro             oa
                                                                                      et             yr
                                                      200                         W               Dr


                                                            50            100                        150        200
                                                                                Speed [km/h]

                                                        Figure 1 Stopping distances versus speeds for horizontal roads

Norms take account of what the driver sees from the stopping distance within a visual field of
±30° horizontally and ±20° vertically, as shown in figure 2 for a dry highway: it is without saying
that the luminances in the visual field are completely different for the speeds of 70 km/h and 130

      Figure 2 A tunnel seen from the stopping distances corresponding to the speeds of 130 km/h (left) and 70 km/h (right)

The effect of the environmental luminance is the generation of a veiling luminance, which
reduces the contrasts of an obstacle and consequently also its visibility.

Pag. 6 of 14                                                                                                      Power controllers – rev. 2

According to the norms, the road luminance that the lighting installation must generate at the
tunnel entrance for making visible a possible (reference) obstacle is proportional to the veiling
luminance, depending on the type of the lighting installation. For the sake of information and not
of lighting design, table 2 reports some typical road luminances in the entrance threshold zone
with maximum daylight level, dry asphalt and no snow as a function of the speed and of the
visibility of the sky over the horizon and at the stopping distance from the tunnel opening. The
big influence of the percentage of the visible sky and of the horizontal meteorological visibility is
clearly evident.

                                Table 2 - Typical threshold luminances
                                        Sky visibility over the horizon [%]
                                            100                50          0
                                     Meteorological visibility distance [km]
                                       10                      20
                                     Entrance threshold luminance [cd/m2]
                           70                -                            75
                          130         320         200                      -

Road luminance diminishes along the tunnels because of the adaptation of the eye to darkness
and reaches the minimum in the internal zone, where UNI 11095 prescribes for single and
double way tunnels a luminance 1,5 or 2 times higher than what prescribed by UNI 10439 and
CEN 13201 (table 3) for the access road.

From the threshold luminance at the entrance to the interior zone the norms foresee a long
transition zone, where the luminance decreases along a standardised curve shown in figure 3.
The entrance threshold zone, where the luminance is at first constant and then decreases to 40%
of the maximum at a distance from the tunnel opening equal to the stopping distance, is followed
by an adaptation zone, whose length is evaluated in running time, since the eye needs always
the same time to adapt to darkness independently of the actual speed: the length scale must be
evaluated according to maximum speed, which in figure 3 is 130 km/h.

                          Table 3 - Classes and luminances of the roads

                                              Road class         Lighting      Road
                         Road                                    category    luminan.
                                             UNI       CEN
                                                                  index       [cd/m2]
                                            10439     13201
              Highways                        A
                                                        M1           6          2,0
              High speed roads               D1
              Important traffic roads        D2
                                                        M2           5          1,5
              Inter-block                    E1
              Block                          E2         M3           4          1,0
              Local inter-zone                          M4           3          0,8
              Local                                     M5           2          0,5
                                                                     1          0,3

 Power controllers – rev. 2                                                             Pag. 7 of 14
                                                                                                   ROAD TUNNEL LIGHTING

                                           Entrance zone               Transition zone                 Interior zone


               Relative luminance


                                                               Permanent lighting

                                                           0                             10                  20 s
                                                                                                  130 km/h
                                             Stopping   0m                                400 m   600 m             800 m
                                             distance                    200 m
               Figure 3 Road luminances in the transition zone

In each zone of a tunnel the wall luminance must be at least the 60% of the road luminance in
order to assure safety in a hostile environment .

The lighting installation should be designed so as to realise the road luminance curve described
in figure 3, where the relative luminance value 100% should be replaced by actual threshold
luminance value at the entrance. Another characteristic to be complied with is the general
uniformity U0, evaluated dividing the average luminance between to subsequent luminaries by
the maximum luminance in the same stretch, and the longitudinal uniformity Ul, obtained dividing
the minimum luminance along an axis of the stretch by the maximum luminance. The norms
prescribe U0 ≥ 0,4 and Ul ≥ 0,6.

The lighting installation can be realised with symmetric luminaries, which emit light equally in
both the running and the opposite direction, or with the so called “counter beam” luminaries,
which emit light mainly against the running direction. In this second case the contrast of the
reference obstacle is improved and a good visibility is obtained with road luminance lower than
with the first method. However, the disability glare for the drivers is higher.

The lighting installation should assure the required road luminance both with the maximum
external sunlight in summertime and/or in winter with snow and sun. When the daylight level
decreases during the day or the seasons, also the luminance generated by the installation must
decrease proportionally.

Traditionally, without regulators the decrease of the road luminance can be obtained switching
out a number of luminaries and realising in this way a number of fixed luminance levels. The
norm prescribe that the ratio between a luminance level and the immediately lower one should
be not higher that 3. For example, in the case of a maximum luminance of 320 cd/m2 like in table
1, the number of lighting levels which permit to reduce the luminance without exceeding the said
ratio down to the interior zone luminance, here supposed to be 3-4 cd/m2, is shown in figure 4:
here the dimming requires 4 switching out levels and 4 electrical supply circuits, complete with
all components. Like in figure 3, also here the logarithmic coordinates are used on the vertical
axis: in this way, all the curves are equally distant vertically.

Pag. 8 of 14                                                                                           Power controllers – rev. 2

                                          320 cd/m

                                    2     106 cd/m
                            100 cd/m

                                                           2                1/3
       Road luminance

                                          35 cd/m

                                          12 cd/m
                             10 cd/m 2

                                          3,8 cd/m
                                                           2                                                                  4 cd/m 2
                                                                                        Permanent lighting
                                                                                                                              3 cd/m 2

                                            Stopping           0                  10                           20 s
                                                                                                   130 km/h
                                                               0m   200 m           400 m              600 m          800 m     1000 m

       Figure 4 Luminance levels with subsequent switching off without regulators

If one continues to switch off luminaries, the distance between the ones still working increases
and lighting on the road can be patch-wise and go under the minimum for general and/or
longitudinal uniformity, with severe dangers for the traffic: to avoid these problems, in the
installations without regulators the number of luminaries must be higher, with also higher
installation and management costs. Vice versa, the Intelux regulators permit to reduce the
luminance of each level to 20% before going to the lower one switching off some lamps: in figure
5 the field of actions of the regulators is hatched.

                                         320 cd/m

                            100 cd/m

                                         67 cd/m
          Road luminances

                                         22 cd/m

                            10 cd/m 2
                                         8 cd/m
                                                                                                                              4 cd/m 2
                                                                                  Permanent lighting
                                                                                                                              3 cd/m 2

                                            Stopping           0                  10                           20 s
                                                                                                  130 km/h
                                                               0m   200 m           400 m              600 m          800 m      1000 m

                        Figure 5 Luminance levels with regulators

 Power controllers – rev. 2                                                                                                    Pag. 9 of 14
                                                                                                                                                ROAD TUNNEL LIGHTING

It can be easily be seen that the number of levels reduces from 4 to 2, together with the electrical
supply circuits, with huge economic savings. Moreover, the risks to slip under the uniformity
values of the norms are much lower, since between two subsequent levels a lower number of
luminaries must be switched off.

Looking at the problem from this point of view, the advantages of the Intelux regulators emerge
clearly against the regulators with a dimming possibility limited to 50%, like the Reverberi models
or in general regulators with transformers (Conchiglia, Irem, ES), which in the present case
would require at least 3 reinforcement circuits. Furthermore, to the higher costs of cables and
electrical components for supplying the higher number of supply circuits it is necessary to add a
higher number of luminaries, equipped moreover with lower power lamps , with consequent
higher costs not only for the installation but also for the energy management, since smaller
lamps have lower luminous efficiency.

Figure 6 shows a general picture of the lighting levels with and without regulators. It is to be
noted that to reach 1 cd/m2 from a starting maximum value of 350 cd/m2 without regulators 5
levels are necessary, 4 using the Reverberi or transformer regulators and only 2 with the Intelux
regulators, which permit to reduce the luminous flux to 20% of the nominal value.

                                                  350   324                 6                                5

                                                  100                       5
                                                                                Regolatori 50% - Reverberi

                                                                                                                 Regolatori 20% - Intelux
                                Luminanze cd/m2

                                                         Senza regolatori


                                                  4,0                       2                                2

                                                        1,3                 1      1,3                       1

                    Figure 6   Lighting levels of road tunnels with and without regulators: the
                               progressive number of the lighting levels is reported within circles.

As already said at point 5, the luminance of the road decreases along the tunnel since trough
both the entrance and the transition zones the eye adapts itself to more and more low
luminance, until the safety minimum in the interior zone is reached, where the norm UNI 11095
prescribes a luminance equal to 1,5 or 2 times the minimum prescribed for the access road by
UNI 10439 and CEN 13201 (table 3) for single and double way tunnels.

In the interior zone of the tunnel, lighting is assured by the permanent circuit , which is not
limited to this zone but runs along the whole tunnel, with the aim of assuring the road luminance
at the minimum safety value along the tunnel when the reinforcement circuits are switched off: by
night, at sunrise and sunset, or by day with overcast skies.
On the contrary, with external sunlight the specific role of the permanent circuit is to assure the
road luminance in the interior zone (figures 4 and 5).

Pag. 10 of 14                                                                                                                                      Power controllers – rev. 2

But the luminance assured by the permanent circuit is not always the same. As reported at point
5, according to UNI 11095 the interior zone luminance should be at least 1,5 or 2 times the
luminance prescribed by UNI 10439 for the access road (table 3), respectively for single or
double way tunnels, provided that the traffic flow is at the maximum level foreseen for that type of
road. When the traffic flow decreases at 50% and 25% of the said value, the lighting category
index is declassified respectively by 1 and 2 units: in practice, in such conditions the road
luminance decreases to about 75% and 50% of the value prescribed for that class of road, with
considerable energy savings. Furthermore, according to UNI 11095 by night the road luminance
in the whole tunnel should be equal at least 1 cd/m2 or to the existing luminance on the access
road if it is illuminated.
However, the most restrictive condition for the permanent lighting installation follows from the
uniformity prescription on road luminance, with a consequent inter-distance between the
luminaries not higher than 10-12 m, because of the necessity to assure the luminance uniformity
with a height of the luminaries of no more than 5-6 m over the road. No problem on the contrary
for the luminance levels, which with such inter-distances are assured through a low wattage high
pressure sodium lamp in each luminaries.

In order to realise the dimming of the permanent lighting installation at the above luminance
levels, with the traditional systems every second luminaries should be switched off, but in this
way it would be necessary to install the luminaries at an inter-distance of 5-6 m, so as to avoid
that switching off every second luminaries the inter-distances of the dimmed installation climb to
more than 10-12 m, reducing the uniformity: figure 7 shows a schematic diagram of a typical
permanent lighting installation realised with a single row of luminaries installed over the passing
lane for a single way tunnel with two running lanes, but the situation would be similar with two
rows of luminaries for a tunnel with three lanes.

On the contrary, the use of the regulators with technology Intelux, but also Reverberi with some
limitations, it is possible to dim the permanent installations with inter-distances of 10-12 m. In this
way, the number of both luminaries and supply circuits is halved, with huge economic savings
for installation and management costs: actually, the lamps of an installation with inter-distances
of 10-12 m emit a luminous flux which is about two times the flux of the lamps with inter-
distances of 5-6 m, which adsorb more energy because of the lower luminous efficiency of the
lamps with small power, even lower that 100 W, which are necessary in the last case.

                    10,00                     10,00                        5,00       5,00       5,00        5,00

                            With regulators                                            Without regulators

 Figure 7   Typical case of a permanent lighting installation realised with and without regulators. Without regulators the
            number of both luminaries and circuits is doubled (higher installation costs) and it is necessary to use lamps
            with smaller power and consequently with lower luminous efficiency (higher energy costs)

 Power controllers – rev. 2                                                                                    Pag. 11 of 14
                                                                                            ROAD TUNNEL LIGHTING

The norms foresee a emergency lighting installation, which, falling the electrical supply system,
is supposed to generate in the whole tunnel a maintained average luminance of 1 cd/m2, without
any specific prescriptions for both general and longitudinal uniformities. In such conditions it is
convenient to split the electrical supply of the permanent lighting in two circuits, base and
emergency, supplying the latter one through an in line electronic continuity generator (UPS), as
shown in figure 8: in this way the lack of the electrical supply system will reduce the road
average maintained luminance of the whole tunnel to at most one half of the normal luminance in
the interior zone and the regulator will further reduce the road luminance to the prescribed
minimum level in order to save the energy supplied by the batteries, whose capacity can be
reduced with reference to the same circuit realised without regulators.

To be noted on this subject that the regulators with either the Reverberi technology and the
Intelux technology can be cascaded with the continuity generators UPS: this means that it is not
necessary to foresee any circuit instead of the regulators.

                                                                Emergency circuit
                              Base circuit

                                   10,00                10,00                       10,00

                                                     With regulators

                Figure 8 Emergency lighting with luminous flux regulators

The use of the luminous flux regulators is extremely useful in the lighting installations for the road
tunnels, since they permit to reduce the number of the electrical supply circuits and of the
luminaries in both the reinforcement and the permanent lighting zones.

In particular, the regulators with technology Intelux assure cost savings both for the installation
and the management of the lighting much higher than with the regulators with technology
Reverberi or anyway with the transformer regulators.

Pag. 12 of 14                                                                                  Power controllers – rev. 2


                                         TUNNEL LIGHTING

                                    TERMS AND DEFINITIONS

        Term                                              Definitions
                             Speed adopted for the design of the tunnel or, if a legal limit exists,
 Design speed
                             maximum permitted speed for assuring a safe driving through the
                             Stretch of road necessary for driving to a complete stop in safe
 Stopping distance           conditions a vehicle which is running at the design speed. It includes
 [m]                         both the distance covered during the reaction time and the braking
 Daily        average        Number of vehicles detected in the period of maximum traffic flow
 traffic flow                which cross a section of a lane during a number of whole days, more
 [vehicles/day]              than one and lower/equal than one year, divided by the days
 Hourly       average        Hourly traffic flow evaluated as the ratio between the daily average
 traffic flow                traffic and the duration of 16 hours/day when it is supposed that the
 [vehicles/h]                highest daily number of vehicles is running.
                             Stretch of open road immediately preceding the entrance portal of the
 Access zone
                             tunnel, along which the driver should be able to see inside the tunnel.
                             Stretch of tunnel where the lighting installation must be reinforced
                             during the day with reference to the night; it includes the entrance and
                             the transition zones.
                             Stretch of the tunnel, whose length is equal to the stopping distance,
 Entrance                    along which the lighting must assure a luminance value such that to
 (threshold) zone            permit to the approaching driver to detect possible obstacles inside
                             the tunnel from a distance equal to the stopping distance.
                             Stretch of the tunnel, which follows the entrance zone, along which the
                             luminance values are reduced gradually in order to allow to the
 Transition zone
                             driver’s eyes to adapt themselves to the low luminance levels of the
                             interior zone.
                             Interior stretch of the tunnel which follows the transition zone, where
 Interior zone               the lighting installation is asked to generate constant luminance values
                             such as to permit a safe driving in the tunnel.
                             Ending stretch of the tunnel where, during the day, the visibility of a
 Exit zone                   driver who is leaving the tunnel is influenced uniquely by the external
 Immediately                 Stretch of the open road immediately following the exit portal of the
 exterior zone               tunnel.
 Entrance                    Average luminance of the stretch of road corresponding to the
 luminance Le                entrance zone.
 Transition                  Average value of the transversal luminance of the road at any point of
 luminance Lt                the transition zone.
 Interior luminance          Average luminance of the stretch of road in the interior zone of a
 Li                          tunnel.

Power controllers – rev. 2                                                               Pag. 13 of 14
                                                                  ROAD TUNNEL LIGHTING

                             TERMS AND DEFINITIONS

        Term                                       Definitions
                      Average value of the transversal luminance of the road at any point of
 Exit luminance Lu
                      the exit zone.
                      Luminance which veils the eye of a driver because of the diffusion
 Equivalent veiling
                      within the eye of the perturbing luminances due to external luminous
 luminance Lseq
 Atmospheric          Disturbing luminance of the vision due to the diffusion of the light in
 luminance Latm       the atmospheric layers within the stopping distance.
 Windscreen           Disturbing luminance of the vision due to the light diffused by the
 luminance Lpar       windscreen of a vehicle.
                      The sum of the disturbing luminances which from the stopping
 Veiling luminance
                      distance disturb the vision of the reference obstacle placed inside the
                      The disturbing phenomenon due to the periodical and quick
                      appearance and disappearance of luminous sources, or of their
                      reflections on the bodies of the vehicles, in the field of view of the
                      drivers, due to an inappropriate distance between the luminaries.
 General uniformity   Ratio between the minimum and the average luminances calculated or
 U0                   measured on the considered surface.
 Longitudinal         Ratio between the minimum and the maximum luminances calculated
 uniformity Ul        or measured along the axis of each lane.
                      The measure of the disability glare produced by the presence of
                      luminous sources within the field of view of the observer, defined as
 Threshold            the percentage of luminance which should be added to the road
 increment TI         luminance in conditions of threshold visibility, with reference to the
                      luminance value which makes visible the same obstacle without the
                      above mentioned sources, always in conditions of threshold visibility.

Pag. 14 of 14                                                         Power controllers – rev. 2

To top