Daylighting Handbook - Exercise

Daylit Area Study and Basic Photometry
Background Reading: DH-I chapters 3, 4 & 5 | MIT lectures: The Source , The Sensor , Photometry Workshop , Massing Studies

In this exercise you will go through some basic photometric measurements and observations of a daylit space with one or more work spaces with high and low visual comfort conditions. You may either pick several work spaces or visit the same work space at different times of day. If possible, all electric lighting should be switched off during your measurements. The exercise consists of three tasks described below. More details are provided in the notes section below.

1. Daylit Area Study A key architectural concept is to divide the floor plan of a building or space into a ‘daylit’ and a ‘non-daylit’ area. Within the daylit area, indoor illuminance levels due to natural light should be adequate, useful and balanced for most of the year. For this task you are asked to follow your own intuition and divide your sample space into a daylit and a non daylit area. In case you are working in a group, each member should conduct this part of the exercise independently. Please mark the two areas on the floor plan of the space and keep your assessment for the Daylight Availability Simulations exercise.

Note: This task can be particularly interesting if multiple individuals (for example a class) conduct the exercise in the same space. As shown in the handbook chapter 5, an overlay of several assessments onto the same floor-plan reveals how subjective the notion of a daylit area can be. Another benefit of the exercise is that you can later compare your personal daylit area assessment to simulated daylit availability metrics in the same space.

2. Photometric Measurements Identify work spaces with good and inadequate visual comfort conditions and briefly describe what is positive or negative in either case. Take a series of workplane illumiance measurements throughout the space and mark your results along with the date and time onto the floor-plan from task 1. Your illuminance measurements should capture the variety of daylighting levels throughout the space. Compare the border of your daylit area boundary to the typical target illuminance for daylit spaces of 300lux. Note down date, time and outside outside horizontal solar radiation during the time of your measurements. The latter you can often get from a local weather station.

Note: An illuminance meter that is going to be used for teaching and architectural practice can be purchased for under $US200. A multi-sensor device such as the Extech Hygro-Thermo-Anemometer-Light Meter is a good choice. For research grade applications, a higher quality illuminance meter (around $US2000) from Hagner, Konica Minolta and others is recommended. High-end sensors require regular recalibration through the manufacturer. While several smartphone-based illuminance meters are available, the author would at this point not recommend their use (see related B.Sc. thesis by Devon Sparks).

3. HDR Photography: Record a set of calibrated HDR images of the work spaces from task 2 from the position of an occupant who is either visually comfortable or not. The images should capture the essence of what you earlier considered to be positive and problematic lighting attributes in the space. In case you wish to later build a calibrated model of your scene, you should also mark down date, time and a reading of the current outside solar radiation. For a glare analysis, you should also take an illuminance meter reading next to the camera lens facing the same way as the lens while taking the HDR photographs.

Note: The purpose of generating calibrated HDR images of a space is generally twofold. One the one hand, these HDR images can later be used to calibrate a daylighting model of the space. Another application is to use the images as precedents. To capture the HDR image you need a digital camera that allows setting different exposure times, a tripod, a software such a Greg Ward's Photosphere and a luminance meter. Luminance meters are more costly (around $US3800) and hence less available than illuminance meters. An argument for acquiring an luminance meter for an educator is to calibrate students' digital cameras for HDR photography. Once calibrated, the calibration file generated with the luminance meter can be used indefinitely with the same camera/lens combination. A tutorial on HDR photography using Photosphere is available here.