Daylight and lighting analysis of I-HUB Building

Up until the late 1800s, all light was from the sun (Daylight) or by some form of fire (candle, oil lamp, a flaming torch, etc). It is measured in lux. Lux is the amount of ‘illumination’ on a surface.

Today we have a range of options to decide on the lighting we would like for our interior based on our needs. However many times we take lighting for granted and end up creating space that is bad for our eyes and our health. Too much light, whether natural or artificial can cause glare which can lead to discomfort to being blinding. Too less strains our eyes and affects our wellbeing and comfort in the space.

An office in the middle of the town at iHubThimphu was assessed for daylight and illumination and the findings will astonish you!

Daylight Study

Of the many methods to calculate or quantify daylight, daylight factor is used here, wherein it is the ratio, expressed as a percentage, between actual illuminance at a point inside a room and the illuminance possible from an unobstructed sky.

The calculation takes into account the glazed area of the window, its transmittance levels, the room interior characteristics while considering skyline obstruction.

The Daylight is calculated from the design sky illuminance of Thimphu which as per the present weather is 12016 lux. The Design Sky Illuminance levels present the diffuse horizontal illuminance value that is exceeded 85% of the time between the hours of 9 am to 5 pm throughout the working year.

This means that the rooms with 1% daylight is read as 120 lux. A room is said to be well day-lit if the daylight falls within 2-5%. Here except room 2 and room 4 all satisfy these requirements. The exceeded daylight factor suggests the need to have external shading due to glare issues. We occupy Room2 as co-working space and we make sure to close our curtains most time of the day so that we don’t stress our eyes with the excessive light flooding in.

The Room 5 and room 6 are the toilet and the kitchen respectively. These rooms have small window opening but the daylight level is quite high. The lack of any glazing on the window and wall tiles will high reflectivity is the cause for that.

However it would be incomplete to not assess the same in terms of the daylight factor measured at the center of the room to understand the distribution of the light.

Using handheld lux meter from VOLCRAFT, we measured the lux levels in the centre of the rooms under cloudy sky condition with outside lux level of 5200 lux.

The above results shows that the daylight factor cannot be generalized for the lux level at the centre of the room since factors as placement of furniture and color affects the lux level at any point. The room 4 is just a meeting space with a sofaset while room 2 (our office) has tables, chairs, closets and large equipment that cause internal reflections that cannot be accounted in the daylight factor calculation. Given the high Window to Wall ratio (WWR), the rooms and absence of any building in its surrounding, the rooms enjoy plentiful daylight throughout the year.

Illumination Study

The lighting audit was conducted to calculate the installed efficacy in terms of lux/watt/m² for general lighting installation. The calculated value is then compared with the norms for specific types of interior installations for assessing improvement options and the saving potential.

The lighting assessment was conducted at night.

The table below summarizes the results obtained. The annual saving considers 4 hours of operation with the lights on from 17:00 to 21:00 hours for 300 days in a year.

The table clearly shows that the rooms are poorly lit and does not create a good lighting environment at night for desk work. The recommendation against all rooms is to install more lights, preferably LED lights to reduce the energy bills. The other recommendation is to put in place good curtains that will not let the light escape out which has been put in place at room 4. The saving takes into consideration the current lighting equipment currently in use and so with incandescent bulbs in Room 1,2 and 3 the annual saving potential increases unless it is replaced with energy efficient light.

Since we have mentioned the need to replace the lighting fixtures, we will first determine the Lumen or wattage that each room will require. We will use the http://www.charlstonlights.com/led-light-requirement-calculator to conduct this assessment for each of the room.


*Rounded off to the nearest based on the base Wattage and to arrive at even numbers

The bar chart presents the changes in the saving scenario using the LED against each room.

From the above calculation, we can conclude that investing in LED has a very promising payback period of just 2 years while it will also significantly contribute to improving the lighting comfort for the end-users at iHub.

Please get in touch with us if you would like to understand the efficiency of daylight or lighting installations at your home/office/space.

Have a great weekend!