The Effectiveness of Blue-Light-Emitting Glasses in Security Guards Exposed to Night Shift Work on Work-Related and General Fatigue: A Randomised Controlled Cross-Over Study

Round 1

Reviewer 1 Report

This is a well written manuscript and a thoroughly conducted study. In line 161 I found a spelling mistake (too instead of to). I think it is important that these findings will be published.

Nevertheless, I have some minor questions, that I think are not addressed in the manuscript so far:

Although one could replicate the corneal melanopic irradiance with the information given in the manuscript, I think it should be mentioned directly in the methods. Either melanopic irradiance or better melanopic equivalent daylight illuminance at the cornea should be reported. It is only 35 lux but with a narrowband blue spectrum, so it is difficult to estimate. 

Together, the low light intensity, short duration of only 30 min and the many confounding factors in real life, seem not to be promising for expecting  any effects (even if studies with nurses have shown some effects).  This should be discussed in more detail (e.g. can melatonin suppression be expected? (see for example Gimenez et al. 2022 J Pineal Research)). And if melatonin suppression can be expected, isn’t it considered to be unhealthy? I think the health issues associated with melatonin suppression should be discussed in the manuscript (only shortly).   

 

 

Author Response

Please see the attachment.

Reviewer 2 Report

General remarks:

Findings from laboratory studies need to be translated to the field. Therefore, the current study using blue light emitting glasses in a real world setting is of great interest. That they do not find any significant differences between their light intervention and the control setting is all the more reason to publish the study due to the importance of publishing negative findings. I only have a few minor comments.

 

Line 26:

“Keywords: Blue light; need for recovery; RCT; field-based study”

The abbreviation for randomized controlled trial is only used in the keywords. This abbreviation should also appear in the main text. And perhaps “shift work” can be added to the keywords.

Line 35:

The “wake-sleep cycle” is usually written as “sleep-wake cycle”.

Line 15-16 and line 58-61:

“Light manipulation is seen as a promising strategy to better align the individual’s circadian rhythms to a rotating shift work schedule.”

“Still, light manipulation is seen as a potentially powerful non-pharmacological strategy to manipulate melatonin production and, thus, better align circadian rhythms with shift work schedules [15].”

Circadian rhythms are only mentioned in these two sentences and in the last sentence of the discussion. Yet, you do not discuss how your light intervention may have shifted the circadian phase of your participants. Especially the sentence in the abstract (line 15-16) makes it seem like phase shifting was one of your aims. Maybe you could add a few sentences in the discussion about possible phase shifts due to the nighttime blue light exposure.

Line 101-103:

“Table 1”

Perhaps you could add to the legend of Table 1 a brief explanation of the two groups to make it clear that both groups received the light intervention and control condition. Now, at first glance, a reader may think one group to be the control and the other the intervention group.

Line 118:

“Measurements”

Since the method section with the description of the intervention protocol is at the end of the manuscript it would be helpful to start the results with one or two sentences about the light intervention protocol. A very brief description mentioning that the light intervention consisted out of 5 weeks with and 5 weeks without the light emitting glasses. As the results are written now, it is difficult to understand without first having to scroll down to the methods.

You may also give this paragraph a different header than “Measurements”. Measurements made it seem like it was a paragraph in the methods where the questionnaires are described.

Line 107-108:

“In total, 14 participants (16%) answered 25 questionnaire items (14 for NFRS and 11 for CIS) incorrectly.”

The abbreviations of both questionnaires should be written out at first appearance in the main text, and not only in the Table legend.

Line 113-114:

“Due to technical problems with downloading stress data from the fitness trackers onto the data platform, we missed some kind of data from all participants.”

Please rephrase or describe what you mean with “some kind of data”. This is a bit vague.

Line 126-128:

“The results show that the use of glasses emitting blue light during a night shift did not significantly reduce need for recovery in the study group: F(1.81, 150.25)=1.40, p > .05, ?2=.00137.”

Compared to baseline or compared to no light emitting glasses?

Line 143:

“Thirty participants (35%) wore the light emitting glasses during seven or more night shifts.”

What was the maximum number of night shifts? How can they have worn the glasses for more than 7 night shifts if there are only 7 night shifts during the 5 weeks?

Line 328:

“Participant were instructed to wear the light emitting glasses for 30 minutes during the first half of each night shifts in the intervention period.”

The plural of participant should be used here.

Did the 30 minutes have to be consecutive minutes or could the participants wear the glasses in bouts of a few minutes that totaled 30 minutes? Why were glasses worn in the first half of the night shift between 23:00 and 2:00? In the discussion you mention longer duration times may improve results. What were the reasons your participants wore the glasses for 30 min and not longer?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf