India is one of the most interesting nations with wide range of climatic conditions which holds a maximum of 8hrs above sunlight during daytime. The Research deals with the field investigation and analysis of the Day light availability inside the office space due to opening of windows which are necessary for the natural ventilation and better thermal comfort in tropical regions usually daytime working can rely on day lighting as the working concept. The whole office space is studied by means of the instrument to know the daylight penetration through the fenestrations. The Research was carried under two conditions opening the Glass Window and closing the Glass window, in which the Results evidently showed the Opened windows had higher range of Illuminance than the closed windows. The Discussions highlighted concludes the Office environment with the Windows open could be better for Day lighting and natural ventilation for thermal comfort. The Experiment was done for three days to know the average illuminance levels and the reflections of the various planes, surface in the Indoors were noted. The Colour usage and the material finishes had an impact in the distribution of the light in the indoor. The Daylight levels reached up to 2000 lux maximum to 500 minimum and average of 700 lux was maintained all around the office with the windows opened during work as per the Guidelines of lighting which is mandatory for office working environment. The Subjective questionnaire survey conducted to the office staff and the respondents were positive and inferred they were visually comfortable and thermally satisfied due to natural ventilation when the windows were opened. The Approach of allowing the day light along with natural ventilation for comfort shall be followed in office spaces for healthy work environment.