**Atthakorn Thongtha \* and Piromporn Boontham**

Department of Physics, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand; Pirompornb57@email.nu.ac.th

**\*** Correspondence: atthakornt@nu.ac.th; Tel.: +665-596-3550

Received: 21 April 2020; Accepted: 13 May 2020; Published: 16 May 2020

**Abstract:** This research focuses on the use of natural lighting integrated into buildings. Cylindrical glass was fitted into the top of our test model, which was 1 m × 1 m × 1 m, which enhanced the light inside it. The glass fitted comprised a single layer (G), two layers (2G), or two layers of glass filled with distilled water (2GW). Each combination of glass increased the number of glass cylinders from two to six. The nine formats were tested indoors using a light intensity of 1000 W/m2 and the temperature was controlled at 25 ◦C. The lowest temperature averaged 34.4 ◦C, which was recorded using only two glass cylinders that had two layers of glass filled with distilled water. The average internal illumination was 549 lux, which agreed with the CIE standard. Then, the two layers of glass filled with water were examined under natural conditions. It was found that the highest average inside temperature was 40.4 ◦C at 1:30 p.m. The average illuminant values for three days were in the range of 300–500–750 lux, which concurred with the CIE standard. Additionally, the use of the 2S-2GW resulted in the conservation of electrical energy consumed by the cooling load and the illumination of the building between 9:00 a.m. and 3:00 p.m.

**Keywords:** energy saving; daylight; heat flux reduction; illumination; CIE standard
