Velux

The International VELUX Award is a competition for students of architecture that runs every second year. We challenge students from all over the world to work with daylight as an ever relevant source of light, life and joy. The award is one of the most important global student competitions of its kind.

Submission is now closed. The jury will review the projects in July and the regional winners will be announced in August.

A simple introduction to daylight simulations in buildings

The use of simulation tools to evaluate building design performance has gained a lot of popularity in the past decades and is today a common asset in the toolbox of many architectural practices. This article introduces some of the basic notions used to perform daylight simulations in 3D models.

Hessenwaldschule, school in Germany. Model and renderings, Christian Vindal Bech (VELUX Group)

How to measure daylight

Daylight levels in buildings can be measured using the light metrics illuminance and luminance, where illuminance has traditionally been used as the metric to evaluate the quantity of daylight in a space, and luminance as the metric to evaluate aspects related to visual comfort and risk of glare.

Illuminance

Illuminance is the measure of the amount of light received on the surface. It is typically expressed in lux (lm/m2). Illuminance levels can be measured with a luxmeter or predicted through the use of computer simulations with a validated software.

Illuminance rendering from Daylight Visualizer

Luminance

Luminance is the measure of the amount of light reflected or emitted from a surface. It is typically expressed in cd/m². Luminance levels can be measured with a luminance meter or through the use of high dynamic range imaging techniques together with a digital camera and a luminance mapping software, and predicted through the use of computer simulations with a validated software.

Luminance rendering from Daylight Visualizer

Daylight glare probability analysis with luminance rendering from Honeybee in Rhino/Grasshopper

How to measure daylight performance

Daylight performance in buildings can be assessed with different metrics, the 3 most common are described here below. Daylight factor is a relatively simple measurement method established long before the use of computer simulation tools, but it has its limitations since it omits direct sunlight. Newer methods are taking advantage of the increased computing power available today and simulate daylight conditions for every hour of the year using recorded climatic data of the sky conditions near the location of the building, and report on the occurence of desired illuminance levels inside the space.

Daylight factor (DF)

Daylight factor (DF) is a daylight availability metric that expresses as a percentage the amount of daylight available inside a room (on a work plane) compared to the amount of unobstructed daylight available outside under overcast sky conditions.

Daylight factor (DF) simulation in a classroom before (left) and after (right) renovation, including a 0.5m perimeter from the walls around the work plane

Daylight autonomy (DA)

Daylight autonomy (DA) is a daylight availability metric that corresponds to the percentage of the occupied time when the target illuminance at a point in a space is met by daylight. It is often used including a requirement for the fraction of the space that needs to be above or equal to the target daylight levels, and in this case referred to as spatial daylight autonomy (sDA). For example: 300 lux requirements to be achieved over 50% of the work plane area for 50% of available daylight hours in the year.

Daylight autonomy (DA) simulation in a classroom before (left) and after (right) renovation, including a 0.5m perimeter from the walls around the work plane

Useful daylight illuminance (UDI)

Useful daylight illuminance (UDI) is a daylight availability metric that corresponds to the percentage of the occupied time when a target range of illuminances at a point in a space is met by daylight. Daylight illuminances in the range 100 to 300 lux are considered effective either as the sole source of illumination or in conjunction with artificial lighting. Daylight illuminances in the range 300 to around 3 000 lux are often perceived as desirable.

Useful daylight illuminance (UDI) simulation in a classroom before (left) and after (right) renovation, including a 0.5m perimeter from the walls around the work plane

By Nicolas Roy, VELUX Group