Lighting is one of the primary areas to be addressed when designing low-sensory stimuli space for Neuro-divergent (ND) clients who have autistic spectrum disorder with or without intellectual disability. Many of the ND are hypersensitive to brightness and flickering of light that are imperceptible to neuro-typical (NT) clients. ND-friendly soft diffused flicker-free lighting seems to be one of the basic elements of neuro-diversity design.
Flickering Light's Negative Effects
Fluorescent lights which typically flicker at the frequency of 100 to 120 Hz are particularly known to cause sensory overload to the majority of the ND. Even some neuro-typical people are prone to various fluorescent light related disorders such as migraines, eye strain, dizziness, nausea, etc.
The fact is, not only fluorescent lights but all artificial lights on AC power source flicker to some extent, especially when they are dimmed. Incandescent lights flicker relatively mildly and less, but these days they may no longer be a practical lighting option. Regular LED bulbs can flicker as harshly as fluorescent lights.
Lighting Design Considerations
So what could be done?
For daytime lighting, maximize the use of indirect natural light. Let natural light bounce on surfaces of the building exteriors and interiors to make it diffused and spread in the space.
Avoid or minimize the use of overhead fluorescent fixtures. Instead, use indirect general lighting, floor lamps, wall sconces, or table lamps with flicker-free LED bulbs. If possible, replace fluorescent bulbs with flicker-free LED bulbs at all lighting fixtures.
Incorporate colored lights and lower wattage lights to create calming environment for all.
When selecting LED light options, two metrics matter:
1) Flicker Frequency: how many times a second the light flickers
2) Flicker Percentage: how much the light's brightness changes within a flicker cycle
The higher the frequency, the better.
The smaller the flicker percentage, the better.
At the regular frequency of 100 to 120 Hz, 10% flicker could cause health issues.
Hence 5% flicker or less is desirable to mitigate detrimental effects.
At the higher frequency of 1250 Hz or higher, 100% flicker would be considered harmless to human health in general at the moment, although not certain if this holds true to the ND's hypersensitivities.
Beware of color-changing LED lights and PWM (Pulse-Width Modulation) dimmable LED lights: they are usually 100% flicker. As such their frequencies should be 1250 Hz or higher if they are to be used in ND-friendly spaces. Otherwise, perhaps better to avoid them.
References / Sources
Bogdashina, O. Sensory Intolerance in Autism. https://www.integratedtreatmentservices.co.uk
On flickering LED light's negative impact on health: https://ece.northeastern.edu
On flicker-free lights: https://www.waveformlighting.com