*Article* **Experimental Investigation of Illumination Performance of Hollow Light Pipe for Energy Consumption Reduction in Buildings**

**Jiraphorn Mahawan and Atthakorn Thongtha \***

Department of Physics, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand; mjiraphorn@yahoo.com


**Abstract:** This work investigates the light illumination intensity, light transmission performance, light distribution on the floor, and daylight factor of vertical light hollow tubes at various incident elevation angles of a light source. The light tubes were made from commercial aluminum alloy sheets and commercial zinc alloy sheets to investigate internal illuminance for buildings and reducing the demand of electrical energy from artificial lighting. The vertical light tubes with a constant length of 0.5 m and diameters of 0.20, 0.25, and 0.30 m were designed in a testing room model, with dimensions of 1 m × 1 m × 1 m. A 20-W light-emitting diode (LED) lamp was used as the light source for the lighting simulations, which was placed away from the top of the light tube. The incident elevation angle of the light source was changed between 0◦ and 80◦ with 5◦ increments. It was found that the elevation angle of the incidence light had an influence on the light intensity distribution on both ends of light tube. The average illuminance performance of both material types increased with an increase of the incidence angle from 0◦ to 80◦ and an increase of the tube diameter from 0.20 m to 0.30 m. The commercial aluminum alloy tube promotes greater light transmission and daylight factor when compared with the commercial zinc alloy tube in each condition. This illuminance measurement demonstrates that the light tube could be included in the lighting systems of some deeper or windowless areas of buildings to decrease the demand of energy consumption in the lighting of buildings.

**Keywords:** daylight; light pipe; light transmission; daylight factor; illumination
