**3.1 Experimental analysis on the Double Light Pipe**

The authors carried out an intensive experimental and numerical analysis on the DLP. The experimental analysis was carried out on reduced scale models of the system, while for the numerical analysis, Radiance and Ecotect were used, two reliable soft-wares commonly used for daylight simulations (Chella et al. 2007, Baroncini et al. 2008, Baroncini et al. 2009, Baroncini et al. 2010) .

Fig. 3. Two dimensional section of a two levels building equipped by a DLP

Fig. 4. Application of Double light pipes in a two levels underground museum.

The experimental data measured on a 1:2 scale DLP in three different tests are shown in the following figures. The results report the illuminance distribution in the passage area measured in 12 internal positions on a horizontal work-plane 40 cm high above the floor and outside of the building close to the collector on the roof-top as well are presented in the following figure.

B

Fig. 3. Two dimensional section of a two levels building equipped by a DLP

Fig. 4. Application of Double light pipes in a two levels underground museum.

following figure.

The experimental data measured on a 1:2 scale DLP in three different tests are shown in the following figures. The results report the illuminance distribution in the passage area measured in 12 internal positions on a horizontal work-plane 40 cm high above the floor and outside of the building close to the collector on the roof-top as well are presented in the

Fig. 5. Measure positions in the experimental tests on the 1:2 scale model of the DLP

Figure 6 shows the results of a test carried out under intermediate cloudy sky between 9 am and 1 pm. The external illuminance ranged between 17 and 76 klux, with a mean value of about 40 klux. It is evident that the interior illuminance trend is very similar to the external one in every position in the absence of direct solar radiation. Some peak values of illuminance observed in positions 1 and 2 close to the corners of the room at about 11 am may probably due to particularly intense reflections from the device. The ratio between Ein and Eext is less than 1 % all over the work-plane.

Fig. 6. Experimental data on a 1:2 scale model of a DLP under cloudy sky

In Figure 7 data are shown regarding an experimental test effected on the same 1:2 scale model of the DLP with intermediate sky with sun, between 9 am and 4 pm, the external illuminance ranging between 18 and 73 klux with a mean value of about 56 klux. In this case, the peaks on the corner of the room are more evident than in the previous test, not only in positions 1 and 2, but also in positions 11 and 12 on the opposite side of the room, probably due to a more significant influence of direct solar radiations. Peaks of illuminance take place at points determined by the hourly positions of the sun in the sky and by the directions of high reflections generated by the system.

Fig. 7. Experimental data on a 1:2 scale model of a DLP under intermediate sky with sun

Finally, in Figure 8, the results of a two - day test on the same reduced scale model under clear sky with sun are shown. The test was carried out between 9 am of the first day and 3 pm of the second day. Corresponding to a more regular trend of the external illuminance, which is characterized by more powerful direct solar radiations (Eext ranges from 11 to 74 klux, with mean value of about 51 klux in the first day and from 11 to 72 klux with a mean value of 55 klux in the second day) the internal illuminance is characterized by very frequent illuminance peaks in various positions. The greater the external illuminance the more frequent the presence of the peaks.

Starting from this consideration, it is likely that high reflections from the DLP involve glare phenomena for the occupants of the environment. In such cases the use of the diffusing film described above can be an effective antidote to this possibility.

In Figure 7 data are shown regarding an experimental test effected on the same 1:2 scale model of the DLP with intermediate sky with sun, between 9 am and 4 pm, the external illuminance ranging between 18 and 73 klux with a mean value of about 56 klux. In this case, the peaks on the corner of the room are more evident than in the previous test, not only in positions 1 and 2, but also in positions 11 and 12 on the opposite side of the room, probably due to a more significant influence of direct solar radiations. Peaks of illuminance take place at points determined by the hourly positions of the sun in the sky and by the

directions of high reflections generated by the system.

0

8.46

9.00

9.14

9.28

9.42

9.56

10.10

more frequent the presence of the peaks.

10.24

10.38

10.52

11.06

11.20

described above can be an effective antidote to this possibility.

11.34

11.48

12.02

12.16

12.30

**hh.mm**

12.44

Fig. 7. Experimental data on a 1:2 scale model of a DLP under intermediate sky with sun

12.58

Finally, in Figure 8, the results of a two - day test on the same reduced scale model under clear sky with sun are shown. The test was carried out between 9 am of the first day and 3 pm of the second day. Corresponding to a more regular trend of the external illuminance, which is characterized by more powerful direct solar radiations (Eext ranges from 11 to 74 klux, with mean value of about 51 klux in the first day and from 11 to 72 klux with a mean value of 55 klux in the second day) the internal illuminance is characterized by very frequent illuminance peaks in various positions. The greater the external illuminance the

Starting from this consideration, it is likely that high reflections from the DLP involve glare phenomena for the occupants of the environment. In such cases the use of the diffusing film

13.12

13.26

13.40

13.54

14.08

14.22

14.36

14.50

15.04

15.18

15.32

15.46

16.00

0

10

20

30

40

**klux**

50

60

70

80

Pos. 1 Pos. 2 Pos. 3 Pos. 4 Pos. 5 Pos. 6 Pos. 11 Pos. 12 Pos. 13 Pos. 14 Pos. 15 Pos. 16

Eext

200

400

600

**lux**

800

1000

1200

Fig. 8. Experimental data of a two - day test on a 1:2 scale model of a DLP under clear sky with sun
