LED Sensitivity Survey: Methods
It is hoped that this survey might serve as a pilot study to inform future research that may be conducted with more scientific rigor. This study suffers from its author being a target survey participant, but I made the decision to create this survey anyway because it seemed that current research efforts were not sufficiently focused on this issue.
This survey was posted on the LEDStrain.org forum in June 2021. The survey requires respondents to confirm that they are 18 years or older and that they understand that their results will be made public for the purpose of informing healthcare professionals, lighting manufacturers, lighting designers, computer/device hardware and software designers, and other members of the public.
The vast majority of the literature review on this website was conducted beginning in July 2021, after having collected initial survey responses. This timing was both because I was still too screen sensitive and my ongoing symptoms too severe to manage extensive research prior to that time and also because the survey results suggested areas for further literature research.
Survey question development:
Posts from 76 users to the LEDStrain.org forum who described their own symptoms were used as the primary basis for survey questions about LED-related symptoms. This examination of forum posts was exhaustive of neither users nor their symptoms, as I conducted this review May 26th-May 30th, 2021 while I was personally still experiencing enhanced LED sensitivity and sleep abnormalities following a 3-hour triggering exposure to flickering ambient LED lights on April 1st, 2021. This meant that I was doing the research while abnormally screen-sensitive, so I stopped once I felt that I had reached the point of diminishing returns in reading more posts. I attempted to be as inclusive as possible of others' experiences, although it is possible that my personal experience of symptoms introduced some bias. The survey includes free response questions to collect other symptoms that I might not have included, either because my examination of the LEDStrain.org forum was incomplete or because forum users might not have fully described their symptoms.
Similarly, I have conducted enough semi-scientific studies on myself to know that all of my self-test data support the hypothesis that light flicker triggers my symptoms and any continuous light source (sunlight or flicker-free LED light of any white temperature or blue) does not. However, I also tried to write survey questions that might also capture other possible underlying causes of LED sensitivity for other people, including the possibility of blue light being a trigger.
Some of the survey questions are based on those in the HARDSHIP questionnaire designed to assess headaches according to the International Classification of Headache Diseases criteria (ICHD-3), Steiner et al. The Journal of Headache and Pain 15, 3 (2014). https://doi.org/10.1186/1129-2377-15-3. These questions were used with minimal modification to assess other headaches not caused by LEDs and were also modified to assess headaches that respondents think are caused by LEDs. Significantly, in addition to the headache descriptions of pulsing pain (associated with migraine) and feeling like a tight band is around the head (associated with tension-type headache), a third descriptor category of a feeling of pressure/swelling around the eye or within the head was added to better capture LED headache sensations of some LEDStrain.org users. "Photophobia" was also further dissected to question about characteristics of light to which individuals might be sensitive, to reflect how LEDStrain.org users' sensitivity varied for different kinds of lights or for different screen conditions. The algorithm delineated in Steiner et al. (2014) for the HARDSHIP survey was used to determine the type of headache for respondents' non-LED headaches.
A search for how to survey sleep abnormalities led to literature on sleep disturbances following concussion with suggestions on how to question patients Mosti et al. (2016). Survey questions were written to attempt to capture experiences of both hypersomnia and insomnia.
Questions about sensitivities to visible flicker or repetitive patterns were included as the IEEE Std 1789™-2015 Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers (2015) discussed these sensitivities as being common in patients with photosensitive epilepsy. As I have noticed myself becoming increasingly sensitive to visible flicker and repetitive patterns since first experiencing LED symptoms, and because other LEDStrain.org users also mentioned similar sensitivities, questions addressing such sensitivities were included.
Survey question modifications after initial posting:
After the first 11 responses (between August 29th, 2021 and November 6th, 2021) questions were added to explicitly query whether survey respondents thought that LED lights caused their symptoms and to query whether survey respondents thought that LED screens caused their symptoms. Prior to this addition, a more complex examination of other survey answers was required to separately evaluate LED light and LED screen sensitivity. After the first 12 responses, the eye medical history question near the end of the survey was edited to include "dry eye disease" in the list of eye conditions on November 7, 2021. Prior to this time, one respondent had written in "dry eyes" in the optional "other" response box. Eye dryness had already been questioned as a symptom attributed to LEDs. On December 14th, 2021, blepharospasm, convergence insufficiency, and strabismus were added as options to the medical history section querying issues with the eyes. Prior to this time no survey respondents wrote in these conditions in the medical history section. One person had written in convergence insufficiency as a diagnosis they had received from a medical professional for their LED symptoms. Blepharospasm was added because it is another photophobia-associated condition. Convergence insufficiency and strabismus were added to be inclusive of the hypothesis that they might play a role in eyestrain for survey respondents. On December 14th, 2021, two questions were added to assess allodynia in the section of the survey generally assessing LED symptoms. These query whether "skin of head is painful to the touch" or "skin of body is painful to the touch. Prior to this time, a question within the LED headache section asked whether the scalp became painful to the touch during LED headache, but it did not ask about pain in the body and this question was inaccessible to those who said that they did not get headaches from LEDs. Prior to this time, one survey respondent had written in that the skin of their body that was exposed to light became painful, but they had not indicated that this was related to physical touch. On December 14th, 2021, a question querying double vision was added. No survey respondents had written in this symptom, but it was added because of its occurrence in eyestrain, dry eye, and concussion.
Archived LED Sensitivity Survey Questions (PDF) - version archived 12/12/21
Tree building to cluster individuals' symptom profiles:
In order to address the question of how much individuals with LED sensitivity have similar symptoms, individuals' symptoms sets were clustered by building a phylogenetic tree. As a geneticist, I have some familiarity with tree-building, but there may be better statistical tools for this purpose that others might suggest. The data was transformed into a form that could be input into the "Simple Phylogeny" tree-building tool at https://www.ebi.ac.uk/Tools/phylogeny/simple_phylogeny/. To do so, survey responses were converted into letters generally used to represent individual DNA nucleotides or subsets of DNA nucleotides, with the following key and with the following color code in the spreadsheet:
A = yes [green]
T = no [red]
W (represents A or T) = sometimes [yellow]
A = migraine; throbbing or pulsing in type with the heartbeat [green]
C = Tension Type Headache; pressing, squeezing or tightening that feels like a tight band is around the head [blue]
G = Pressure that feels like there's swelling in or around the eye or deeper inside the head. The pressure is continuous and comes with continuous pain [black]
M = "probable" migraine according to the HARDSHIP algorithm [gray]
V = "probable" tension-type headache according to the HARDSHIP algorithm [gray]
- = question not relevant
An "outgroup" row was created in the spreadsheet containing the hypothetical responses of an individual unaffected by LEDs.
Survey responses relevant to LED symptoms, but not other headache symptoms, that had been converted into nucleotide code were pasted into a text editor. A FastA file was created containing a header for each individual (with the entry timestamp) followed by a string of letters encoding the survey responses for each individual. The outgroup was included and multiple copies of the outgroup entry were made, each with a unique header, so that the tree-building program would properly identify the outgroup in order to root the tree. The FastA file was imported into https://www.ebi.ac.uk/Tools/phylogeny/simple_phylogeny/ and a tree was constructed using the default parameters:
Tree format: default
Exclude gaps: off
Clustering method: neighbor-joining
After the tree was built, the branch length was displayed as "real." The image of the tree was saved, extra outgroups at the base of the tree were deleted from the image, and extra numbers added by the Simple Phylogeny program were deleted from the image.
In the spreadsheet, the rows of individuals' symptoms were reordered to reflect the order of individuals in the tree. The data was transposed 90° to better display the survey questions along with their answers.