The effect of blue light filter on visual and task performance

Abstract

Purpose:

This study aimed to determine the effect of the blue light (BL) filter on the different tasks performed on a laptop on a daily basis.

Methods:

Forty subjects were required to perform a 45-minute task on the laptop screen with or without the BL filter on two different days. In the first task, subjects were made to watch a video. In the second task, subjects were made to read a passage from the laptop for 3 minutes, and reading speed was calculated. In the third task, subjects were made to enter the data on the laptop. The time taken to fill in the data was recorded. After the completion of the task, questionnaires were administered. Pre- and post-task accommodative tests were performed.

Results:

Forty emmetropes with a mean age of 21 ± 2 were recruited. In visual performance, the subjective response showed a significant difference in visual fatigue level with and without the filter. A statistically significant difference was seen in reading speed and data entry during task performance with and without the filter. Pre- and post-task accommodative parameters showed variable responses.

Conclusion:

This study showed that the use of a BL filter improves task performance, but subjectively, people experienced more visual fatigue while using the filter.

Blue light (BL) (400–480 nm) is a characteristic of digital devices such as tablets, computers, and smartphones. With their light-emitting diode (LED) backlit screens, such digital devices expose the human eye to BL. The BL emitted by the screens may improve several aspects of cognitive performance, such as alertness, sustained attention, working memory, and declaration memory. The potentially damaging effect of BL has been examined in many previous studies. This part of the visible spectrum may be responsible for damage to retinal photoreceptors and for altering the body's circadian rhythm by suppressing melatonin production. The abovementioned effects are short term. In addition, long-term effects such as maculopathy may have resulted from prolonged exposure to the BL emitted by an LED backlit computer screen.[1]

Owing to the high proportion of wavelengths emitted by LEDs, the impact of BL on the eye has gained increased interest in recent times. This is particularly relevant nowadays given the substantial number of hours being spent by many, or perhaps most, individuals viewing screens in modern life. Furthermore, viewing these displays is associated with a high prevalence of both ocular and visual symptoms. These have been described collectively as digital eyestrain.[2]

Various BL filtering techniques are designed to block the amount of BL entering the eyes during screen viewing. There are BL filters, blocking lenses, and BL filtering intraocular lenses that have been widely used. BL emissions from computer screens may be decreased by BL filters by adding a physical filter, changing the display from white mode to night mode, or using a BL filter application (app). Electronic devices are suggested to be used in filter mode to reduce screen luminance, or that specific colors be blocked to protect the user's eyes from the effects of BL.[1]

This study was performed to determine the effect of the BL filter on accommodative parameters, visual fatigue, and task performance while using a digital device.

Methods

This experimental study was conducted on 40 emmetropic subjects between the ages of 19 and 23 years. The institutional ethical committee approved the study protocol, and written informed consent to participate in the study was obtained from all subjects. The experimental purpose and procedure were first explained to the participants. All subjects underwent a preliminary workup that included distance and near visual acuity at 6 meters and 40 cm, respectively, which were measured using a logarithmic of the minimum angle of resolution (LogMAR) chart. Individuals with distance visual acuity equal to or better than 6/6 and near vision N6 were included in the study. Subjects with a history of ocular or systemic disease, spectacle, and/or contact lens wearers or those using any BL protection products were excluded. The near point of accommodation (NPA) was measured both monocularly and binocularly. The accommodative facility (AF) was measured using ±2.00D flippers. Subjects were given a demo to familiarize themselves with the laptop. Night mode was used, which is a BL filter designed to block BL emitted by the screen of the Lenovo laptop. It is a display mode that changes the color to a warmer version of itself. Here, the strength was kept at 100%.

The test was conducted under two conditions: with and without the filter, with the two trails separated by a period of at least 48 hours. On the first day, no filter was used, while a filter was used on the third day. The order of using the BL filter or using no filter was selected randomly to get unbiased results. Dark adaptation was given for 10 minutes before the test to stimulate night vision. In the first task, subjects were asked to watch an episode of the Tom and Jerry cartoon for 25 minutes. In the second task, subjects were made to read material aloud (to ensure compliance) from a computer at a viewing distance of 50 cm for 3 minutes. The reading material comprised paragraphs from the International Reading Speed Texts (IReST) standard reading speed chart. Reading speed (words per minute) was noted. The computer text was displayed using Microsoft Word software.

In the third task, subjects were told to enter data on the laptop from the given printed material, and the time taken was noted down. Furthermore, post-task accommodative tests were conducted. At the end of the tasks, subjective visual fatigue and image quality were assessed using the questionnaire developed by Aaras et al.[3] The first section included 16 questions based on symptoms related to visual fatigue. Each question was classified into the following three categories, and each statement was rated from “0” to “2,” that is, if the symptoms were “extremely noticeable,” then they were graded as “2”; if “somewhat noticeable,” then “1”; and if “not noticeable at all,” then “0.”

The second section included eight questions on image quality. The frequency of the overall quality of the monitor screen was classified into nine categories. That is, if the quality was “worst,” then they were graded as “9”; if “imaginable,” then “8”; if “awful,” then “7”; if “poor,” then “6”; if “marginal,” then “5”; if “passible,” then “4”; if “ok.” then “3”; if “good,” then “2”; if “excellent,” then “1”; and if “best imaginable,” then “0.” After adding the ratings, the overall score was calculated.

The data were statistically analyzed using IBM Statistical Package for the Social Sciences (SPSS) version 19. The mean and standard deviation (SD) were calculated. The comparison between the mean groups was conducted using analysis of variance (ANOVA) at a 95% confidence interval (CI). The comparison between the two groups was performed using a paired t-test at 95% CI. A P < 0.05 was considered statistically significant.

Result

The experimental study was conducted on 40 participants according to the inclusion criteria between the age groups of 18–23 with a mean age of 21 ± 2. Of the 40 participants, two (5%) were males and 38 (95%) were females.

The results of the objective and subjective evaluations were analyzed and organized. The results are described as follows.

The effect of BL filter on task accommodative response

The analysis of task performance revealed a statistically significant difference in the post-usage of the laptop with and without the BL filter, monocularly and binocularly. The AF found a statistically significant difference in a BL filter and a BL level monocularly and binocularly. However, no significant difference was seen in the AF for BL filter binocularly[Table 1].

Table 1.

Descriptive values (mean±standard deviation) of near point of accommodation and accommodative facility assessed for with and without filter conditions using one-way ANOVA at 95% confidence interval

Accommodative parameters	Testing eye	Pre-task	Post-task		P
			Without filter	With filter
		Mean±SD	Mean±SD	Mean±SD	Without filter	With filter
NPA	RE	11.27±1.76	10.79±1.88	10.62±1.71	0.013	0.014
	LE	10.73±1.76	10.22±1.64	10.08±1.64	0.241	0.001
	BE	10.01±1.68	9.74±1.80	9.50±1.71	0.009	0.047
AF	RE	13.20±5.15	14.02±6.18	14.10±6.55	0.000	0.000
	LE	13.50±5.19	14.42±6.44	14.62±6.55	0.000	0.007
	BE	12.01±4.72	12.40±4.89	13.02±5.53	0.000	0.095

NPA=Near point of accommodation; AF=Accommodative facility; RE=Right eye; LE=Left eye; BE=Both eyes; SD=Standard deviation

The effect of BL filter on visual fatigue

For the subjective response, the results analyzed by paired t-test for the BL filter indicated a significant effect on subjective visual fatigue. The mean scores for visual fatigue were 8.05 ± 5.55 in the BL filter condition and 7 ± 5.41 in the without filter condition [Table 2] [Fig. 1].

Table 2.

Descriptive values (mean±standard deviation) of reading speed, data entry, and visual fatigue using a paired t-test at 95% confidence interval

	Mean±SD	P
Reading speed
Without BLF	161.40±50.93	0.000
With BLF	161.10±40.28
Data entry
Without BLF	423.55±100.43	0.000
With BLF	407.12±96.59
Visual fatigue*
Without BLF	7.00±5.41	0.000
With BLF	8.05±5.55

BLF=blue light filter; SD=standard deviation

Figure 1.

Graph demonstrating the visual fatigue score without and with BLF using a paired t-test at a 95% confidence interval

The effect of BL filter on reading speed

Analysis of reading speed showed a statistically significant difference with and without the BL filter condition, showing improvement in reading speed [Table 2] [Fig. 2].

Figure 2.

Graph demonstrating reading speed scores with and without BLF using a paired t-test at a 95% confidence interval

The effect of the BL filter on data entry

The analysis of data entry revealed significant differences between with and without BL filter conditions [Table 2] [Fig. 3].

Figure 3.

Graph demonstrating data entry scores with and without BLF using a paired t-test at a 95% confidence interval

Discussion

In this study, the effect of the filter on three different task performances conducted in our day-to-day life was observed.

The results showed that the BL filter and BL both had a similar effect on accommodation while performing the tasks on the laptop screen. A reduction in NPA values was observed, which means that the subjects had to accommodate less as compared to normative values with and without the filter, monocularly and binocularly.

The improvement in the AF was seen when compared to the normative value with and without the BL filter, monocularly and binocularly. Some authors have reported that the accommodation response is an indicator of fatigue.[4] Another study has shown that individuals with visual discomfort showed greater stability of accommodation with tinted lenses, although these changes seem to be independent of the color specificity of the lens.[5] Our result supports the findings of a study conducted by B Redondo et al.,[6] where the variability of the accommodation was found to be sensitive to the task, showing greater fluctuations over time irrespective of the BL level.

The visual fatigue score showed that the patient felt tired after using the filter. This could be due to different factors, such as difficulty focusing and foggy letters. Some even felt that the screen looked dimmer and less colorful, and the subjects had to put in extra effort so they could maintain the screen quality.

Regarding the use of blue-blocking (B-B) filters, some studies have reported a reduction in visual symptoms associated with computer use,[7] while others did not observe a difference regardless of the type of the B-B filter.[8] Our results differ from both studies, and the B-B filter used in the present study affected the level of visual discomfort. These findings are irrelevant given the controversy surrounding the proposed harmful effects of BL on the visual system and the widespread commercialization of BL filters.

Reading speed revealed a statistically significant effect, with a better reading speed for the B-B filter condition. It should be noted that this improvement in reading speed while using the B-B filter occurred during the entire reading task, and therefore, these effects seem to be independent of visual fatigue. The use of filters with a yellowish tint has improved contrast, which may account for the increased reading speed.[9] Cognitive factors were not considered while recording reading speed. Previous researchers have found that either higher screen performance or high contrast can improve task performance.[10]

The impact of the BL filter on data entry speed was also examined. Our study reported an improvement in data entry speed with the BL filter. It is found to be statistically significant. The reason was that there was less glare coming from the screen. However, there is a lack of clinical evidence to support the notion that B-B filters influence task performance and further studies are needed in this regard.

Moreover, based on the current findings, we state that the prescription of B-B filters for the changes in ocular accommodation associated with computer work is not scientifically justified.

This study had some limitations. First, we chose a commercially available B-B filter. However, other types of B-B filters may lead to different results on accommodative parameters. Secondly, the accommodative and reading speed responses may be dependent on refractive error and future studies should consider dividing their experimental sample into different refractive error groups. The current study only measured the short-term effects of BL; the long-term effects can be explored in the future. Finally, subjects were aware of whether they were performing the laptop reading task with or without the filter, and their reading speed and data entry speed could have been influenced by this bias.

Conclusion

The BL filter influenced the accommodative response with and without a filter. Our study observed improvement in task performance when the filter was used; however, the BL filter led to visual fatigue when measured subjectively.

This outcome hypothesizes that technology would provide a good way to improve viewing comfort and that task performance would be enhanced if BL was filtered while the display quality is maintained. Good display characteristics are important factors for task performance.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.