Spotlight on Diversity October 2022
For National Disability Employment Awareness Month IESNYC shines a light on light sensitivity…but softly, with good glare control
Lighting Guidelines for Persons with Light Sensitivities
Nearly all of us are susceptible to glare. Whether it’s a bright sunny day or electric lighting that causes reflected glare or direct glare, light can negatively affect our ability to see (disability glare) and sometimes cause unease or pain (discomfort glare), where we reflexively look away, squint, or shade our eyes. Light sensitivity, or photophobia, is common for people with eye conditions like eye injury, dry eyes, or cataracts, and persons with various types of sight loss. Numerous other conditions cause or occur in conjunction with photosensitivity. These include medication side effects or recreational drug use; brain injuries; and migraines, before, during, and after a headache. Note that about three out of four people who have migraines are women.
Sensory processing disorder is not recognized as an “official” diagnosis, but sensory issues, including photophobia, are included as a common symptom of autism spectrum disorder and can be a challenge for persons with attention deficit hyperactivity disorder (ADHD). Symptoms include dizziness, nausea, anxiety, irritability, fatigue, and discomfort. Where photosensitivity occurs in children, a case of autism, sensory processing disorder, ADHD, or obsessive-compulsive disorder may be difficult to diagnose. In both children and adults, a sudden onset of photosensitivity may be due to meningitis, requiring immediate medical care.
Light flicker (or temporal light modulation) is also associated with several conditions. In addition to seizures brought on by flashing or flickering lights (photoepilepsy), some individuals are more likely than others to be affected by flicker-induced eyestrain, headaches, vertigo, nausea, and emotional distress or behaviors. Odd visual distortions, stroboscopic effects or ghosting, can impair seeability for human observers and interfere with video and security cameras.
Unfortunately, some people are sensitive to light without there being an eye condition or other identified physical cause. Typically, these individuals will remain light sensitive over the course of their lifetime, or their sensitivity will gradually increase as they age.
But where an underlying cause can be identified and treated or not, there are measures that individuals and designers can take to accommodate persons with light sensitivity.
Personal Light
Special attention to glare and personal control of lighting instruments can serve persons with low vision and light sensitivity. An aimable task light with good glare control can facilitate close work or visually intensive tasks more comfortably.
Window shades and dimmers can help control glare, and allow an occupant to choose the appropriate ambient brightness for their home. Meanwhile, consistent light levels throughout a home can eliminate large swings from bright to dark as occupants move from room to room. Task lighting, addressable fixtures, and direct dimming can help customize shared workspaces. The Thomas Pocklington Trust has developed a lighting guide for blind and partially sighted persons, which can provoke thoughtful discussions around lighting for persons with photosensitivity. Note particularly the advice around uniform lighting and using contrasting materials in order to reduce falls. Avoid specular finishes and furnishing that might catch a disruptive reflection.
In addition to adjustable blinds, designers can ensure that seating is available that faces away from windows. Employers can provide a respite area, a room that can be dimmed or darkened overall with low-level safety or task lighting.
Flicker
Occupants can be impacted whether flicker is perceptible or imperceptible. Flicker can be directly apparent when observing a light source, or it can induce effects on the visual field (like a stroboscopic effect or phantom array effect). Naomi Miller and her peers at PNNL have done extensive investigations on flicker in LED light sources, and IESNYC recommends keeping up with the latest findings.
Flicker is the dance of the LED, the driver, and controls. It is variable in frequency, intensity, duty cycle (that is, percent of time above a certain intensity), relative motion, adaptation level, and the shape of the waveform. Studies have found that deleterious impacts increase with longer exposure, high average brightness, high contrast, large affected portions of the visual field, when both eyes are being stimulated, and color contrasts.
Humans exhibit wide variations in sensitivity to temporal light modulation, and it is important to learn how many are vulnerable to discomfort, health effects, or reduced productivity caused by undesirable TLM, and to what degree. Research into the neurological pathways that relate TLM (visible or not) to physiological responses such as autistic behaviors, headaches, malaise, migraines, distraction, or annoyance is scarce. Once more is known, lighting standards organizations should establish criteria for metrics to promote comfort and health, balancing those outcomes with cost and functionality implications for lighting products. (Miller et al. 2022)
Further, studies usually include “normal” or average vision, not more sensitive observers. Though determining “safe” levels of flicker is not currently feasible, Miller is clear in her recommendations to designers:
- Observe actual light fixtures at full luminance and fully dimmed, especially where color tuning is employed.
- Use a wand or wagging finger to detect stroboscopic effects.
- Purchase a quality handheld flicker meter (measuring frequencies up to at least 2000 Hz)
- Even though the metrics are imperfect, educate yourself and your peers on flicker metrics and demand that manufacturers publish data.
- Ask clients and occupants about sensitivity to flicker.
- Determine where machine vision or particularly kinetic tasks demand special attention.
- Include flicker thresholds in your specifications.
- If you suspect flicker in a sample or job site, use the slow-motion capability on your smartphone; it can produce telltale flashing or other flicker artifacts.
This information is intended to raise awareness and provides a general overview and solutions that will not apply to everyone, in all cases. Consult with medical professionals and end-users to find out if this information applies to a specific lighting application and to keep abreast of the latest findings and recommendations on the subject.
