Reflections on light and vision impairment
- Kristoffer Negendahl
- Apr 2, 2024
- 6 min read
Ever wondered if the lighting in our buildings and city streets is fair for everyone? It's not just about whether the rooms are evenly lit, but rather if the natural and artificial light we've painstakingly planned actually meets everyone's needs! Spoiler alert: it doesn't. But why is that, and what can we do to make it better? Let's shed some light on the matter!
As an engineer who has worked with light design for a number of years, I realize I have wondered about this very late in my career. In the next few minutes, I will try to explain why few, who work in the building industry with lighting have yet to accommodate people with various degrees of blindness and vision impairments.
Globally, at least 2.2 billion people have a near or distance vision impairment. In at least 1 billion of these, vision impairment could have been prevented or is yet to be addressed.
The demand and the codes
Building codes serve as the baseline requirements dictated by stakeholders involved in the construction process, including investors, builders, sellers, and leasers. It's rare, that anyone sets higher requirements than the code. The codes set the standard for design parameters, limiting how far a project will deviate from these requirements. And, when it comes to "soft engineering" aspects like lighting comfort, the drive to exceed traditional analysis methods and create superior buildings that prioritize occupants' well-being is scarce. While architects generally recognize the importance of light, particularly natural light such as daylight and sunlight, there's often a gap between this recognition and the actual implementation of design strategies that enhance lighting conditions for building users.
Vision impairment poses an enormous global financial burden, with the annual global cost of productivity estimated to be US$ 411 billion.
Light analysis as a discipline
Efficient natural lighting plays a pivotal role in crafting buildings that resonate with their occupants on multiple levels. Beyond merely illuminating spaces, a well-designed daylight environment offers visual and thermal comfort, fostering a sense of wellbeing and satisfaction among occupants. Moreover, strategically harnessing natural light serves as a passive means of energy conservation, enabling occupants to rely less on artificial lighting sources. By exploiting natural illumination, occupants can minimize electricity usage, thereby diminishing the building's environmental impact and lowering operational expenses over time. In essence, prioritizing good natural light not only enhances the overall user experience but also contributes to sustainability efforts and cost savings in building management. Analyses of light both naturally occuring and delivered by artificial means typically are done by expert simulationists using building performance simulation tools and 3d models.
Light analysis is commonly linked with assessments of energy usage and thermal comfort in architectural and engineering contexts. Additionally, in some instances, glare analysis is incorporated to address potential discomfort caused by excessive brightness or contrast. This combined analytical approach ensures that designs not only optimize natural light but also consider energy efficiency and occupant comfort. By integrating these analyses, professionals can develop more sustainable and user-friendly buildings, striking a balance between environmental responsibility and occupant wellbeing.
Designing for daylight requires a meticulous equilibrium between managing heat transfer, controlling glare, ensuring visual comfort, and accommodating fluctuations in natural light levels. Various techniques, such as shading elements, light shelves, courtyard designs, atrium configurations, and window glazing options, are commonly employed to optimize daylight utilization. Key factors influencing daylighting design encompass the building's orientation, the dimensions and placement of windows, the choice of glazing materials, the reflectivity of interior surfaces, and the arrangement of interior partitions.
Typical ways to evaluate daylight:
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 (Hopkins,1963)
The higher the DF, the more daylight is available in the room. Rooms with an average DF of 2% or more can be considered daylit, but electric lighting may still be needed to perform visual tasks. A room will appear strongly daylit when the average DF is 5% or more, in which case electric lighting will most likely not be used during daytime (CIBSE, 2002).
BREEAM uses DF as a quality indicator in commercial and residential buildings: "at least 80% of floor area in occupied spaces has an average daylight factor of 2% or more”. LEED and DGNB has similar requirements.
Daylight Autonomy (DA/sDA)
Useful Daylight Illuminance (UDI)
Daylight Glare Probability (DGP)
No analytical approach for visual impairments in engineering
No emphasis or special considerations for vision impairment are implemented in regulations, codes, or even voluntary sustainability schemes (i.e. LEED, BREEAM or DGNB). This is not only concerning but it is entirely possible, that our current measures (from daylight factors to glare probability) are the wrong measures of "sufficient" and "efficient" light. Few available guidelines mention ways of how to quantify or "measure" light, what properties with distinct metrics the light sources should have, and what is "enough light". However a good resource is Poclington who suggest minimum illuminance values for residential spaces (see also table further below).
Vision loss can affect people of all ages; however, most people with vision impairment and blindness are over the age of 50 years.
We seem not to have any standard guidance metrics and thresholds when it comes to various types of impairments. The best we have is studies performed by different research teams e.g. Wittich et al. who found that the color temperature and lux-levels preferences are different from non-impaired sighted people. By using a reading apparatus called LuxIq (https://jasperridge.net/) see also figure below they found that more intense light is needed, but less obvious that "warmer" light is preferred:
People with no light impairments | People with light impairments | |
Light intensity (Lux) | ~ 2000 lux | ~ 3000 lux |
Color temperature (K) | ~ 5200 K | ~ 4700 K |
The LuxIQ Light Exam System (http://jasperridge.net/)
Whether this applies to wayfinding and general lighting conditions in buildings and cityscapes is not known. If these illuminance levels are required for ordinary tasks, the lux levels in our building codes are 1500% off as typical required values are 200 lux (or daylight factor of 2%).
Perhaps it is time to reinterpret the current building codes for minimum standards for lighting in spaces where all people are present. At minimum new and higher illuminance thresholds need to be established for all building coded spaces - and we may look into at least 50% increase if the ratio between non-light-impaired and light-impaired people if the standardized test for low vision lighting can be transferred to spatial lighting and wayfinding. For now suggested values for minimum illuminance values may be used as shown in below table:
Room type | Typical minimum requirement (Lux) | Minimum illuminance (lux) for someone with visual impairment and dementia |
Hallways | 50 | 300 |
Dining/living rooms | 100 | 300 |
Kitchen | 200 | 600 |
Bathrooms | 100 | 300 |
Bedrooms | 100 | 200 |
Stairs | 100 | 150 |
Source: Lighting in and around the home (Poclington)
New types of light-measures needed
In a discussion with Jennifer Veitch, an expert in lighting design and psychology (Principal Research Officer in the NRC Construction Research Centre in Canada) current lighting requirements may be revised in several areas. One area in which lighting fixtures are yet to be systematically reviewed is the fixture's "flickering effect" on people. According to flickersense.org flickering fixtures and screens pose significant public health risks, particularly in places like schools. Also known as flicker vertigo, or the Bucha effect, and according to e. Rash the imbalance in brain-cell activity caused by exposure to low-frequency flickering (or flashing) of relatively bright light as Flicker vertigo can cause physiological symptoms ranging from mild discomfort to unconsciousness. Although several factors are known to influence susceptibility to and the onset of flicker vertigo, their effects are still not fully understood.
Another area that may need to be systematically included in regulations and analyses of buildings' and public spaces' performance is how people experience contrast in these spaces. This particularly pertains to wayfinding, a concern often overlooked by individuals without visual impairments. In a discussion about this particular issue Chris Downey (http://arch4blind.com) mentioned that contrast may be as important as the light (lux) levels itself, and one of the challenges of determining "the right amount of contrast" is that contrast is percieved differently under various lighting conditions. For instance under sunlight, and overcast sky as well as in the lab vs. at the site. We need better ways to determine and set requirements for contrasts in spaces.
In conclusion, we still have to understand how people with light impairments perceive light, but it is clear that lux alone cannot describe how well-lit a space is. We need to take into account at least three more aspects of light performance: color, flickering, and spatial contrast.
Sources
Hopkins, R. G. (1963) Architectural Physics: Lighting, London: Her Majesty’s Stationery Office.
CIBSE (2002) Code for Lighting, Oxford: Chartered Institution of Building Services Engineers.
Reinhart, C., Walkenhorst, O. (2001) Dynamic RADIANCE-Based Daylight Simulations for a Full-Scale Test Office with Outer Venetian Blinds, Energy and Buildings, 33:7, pp. 683-697)
ESNA (2013). LM-83-12: Approved Method: IES Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE). The Illuminating Engineering Society of North America (IES). http://www.ies.org/store/product/approved-method-ies-spatial-daylight-autonomy-sda-and-annual-sunlight-exposure-ase-1287.cfm (accessed:2014-12-10)
Mardaljevic, J., Andersen, M., Roy, N., Christoffersen, J. (2012) Daylighting, Artificial Lighting and Non-Visual Effects Study for a Residential Building
R.G. Rodriguez, J.A. Garretón and A.E. Pattini. An epidemiological approach to daylight discomfort glare, Building and Environment 113 (2017) 39-48. https://doi.org/10.1016/j.buildenv.2016.09.028
Wittich W, St Amour L, Jarry J, Seiple W. Test-retest Variability of a Standardized Low Vision Lighting Assessment. Optom Vis Sci. 2018 Sep;95(9):852-858. doi: 10.1097/OPX.0000000000001275. PMID: 30153238; PMCID: PMC6133227.
Clarence E. Rash, Awareness of Causes and Symptoms of Flicker Vertigo Can Limit Ill EffectsHuman Factors & Aviation Medicine March-April 2004