Soon-to-be Postdoctoral Researcher, Malisa Burge explores why your mood might not just be about stress or study, it might be about whether your light patterns are working with your body or quietly working against it.
By Malisa Burge, (soon to be) Postdoctoral Researcher, Flinders Health and Medical Research Institute (Sleep Health)
Have you ever fallen asleep in an in-person class? And then had your lecturer call on you to answer a question you were unfortunately unconscious for?
Well, I have, and weirdly, that same lecturer went on to be my internship supervisor, my honours supervisor, my PhD supervisor, and is now my current boss: Professor Sean Cain (sorry Sean). I did ask him years later if he remembered. Thankfully, he didn’t. It was unforgettable for me.
At the time, I thought I had chronic fatigue. I was going to my GP trying to figure out why I was so tired all the time. I was juggling full-time psychology study at Monash University with part-time work. To help pay my rent and bills, I was pulling at least one double shift a week: barista work starting at 5:30am, then bartending until late. On days when I wasn’t working or studying, I’d sleep in to compensate for how exhausted I felt.
What I didn’t know then
Our circadian rhythms are internal ~24-hour biological clocks that regulate nearly every cell within our body. These clocks coordinate when we feel alert or sleepy, when our body temperature rises and falls, and when various hormones are released. In our evolutionary history, it has been adaptive to synchronise these internal processes with the external cycle of day and night – the rise and fall of the sun. For example, alertness and digestion during the day, and signals for sleepiness during the night.
Light is the primary cue that synchronises our internal clocks with the outside world and therefore determines which functions should be occurring at what time. Light = day processes. Dark = night processes. Then came… electric lighting. If we compressed our entire human history into 24 hours, electric lighting would have appeared at 11:58pm (in the last 2 minutes). Safe to say, this ancient system was not prepared for our ability to control lighting whenever we wanted. What had been clear, consistent signals for day and night, have become muddled. Which is confusing to our circadian clock and our entire body.
It’s only now, working in sleep and circadian research, that I can see what I thought was chronic fatigue was probably circadian disruption from my irregular sleep and light exposure patterns.
Bright light at 5:30am. Bright light at midnight in the bar. Sleeping (in darkness) until midday on my days off. And then cramming for assignments till very late at night under overhead lighting—using the brightness, whether consciously or not, to help keep myself awake. A highly irregular light pattern my body wasn’t built for.
At the time, I didn’t know why this was problematic. Or the effect that the night light was having on my circadian system. Light at night suppresses the major sleep promoting hormone melatonin, and can shift the timing of our circadian clock, essentially telling our brain it’s still daytime when it should be preparing for sleep. The overhead lighting we commonly use in our homes are bright (standard LEDs range from 100 to 300 lux) and are bright enough to affect the production of melatonin. The average person suppresses melatonin by 50% at just 30 lux, my at-home lighting was 3 times that! I was getting too much light when I should have had darkness, and sleeping through the bright morning light my circadian system needed.
But it’s not just the immediate effects on sleep that matter. This pattern of too much light at night combined with insufficient light during the day is linked to higher rates of depression, anxiety, and poorer overall health. I was essentially giving my body all the wrong signals at all the wrong times.
We now study these things in the lab: looking at someone’s light pattern and providing reports to inform them about what they’re doing well and what they could improve. Are you getting too much light in the evening? Not enough light in the morning? Are you going to bed at the same time every day and night? Had I been a participant in one of my own studies, my report would have plenty to say.
When it all connected
It was probably unsurprising that during my undergrad I was suffering from bad mental health. I was about 19 when I visited my family GP, told her I was overwhelmed, burnt out, and really struggling. I was already in therapy and wasn’t getting any better. She did an assessment, diagnosed me with depression, and prescribed me one of the most common antidepressants.
For me, there was an immediate response. Within weeks, my mood had lifted, my brain fog reduced, and I was able to enjoy things that I previously enjoyed. While antidepressants work for some people, 1 in every 2 people report not feeling satisfied with the first antidepressant they try.
Our lab is trying to figure out why individual responses vary so much. We’ve shown that people with depression on average have a decreased sensitivity of their circadian clock to light, which may mean they aren’t benefiting as much from the positive effects of daytime light. Interestingly, we’ve also shown antidepressants increase this sensitivity to light, which may be the mechanism by which antidepressants improve mood.
This got me thinking: if increased light sensitivity is key to antidepressant effects, how might light improve mood? In my own paper, published last year, I found that if you increased the amount of light that the circadian system is most responsive to (blue light) during the day, we could reduce the number of negative thoughts people had about themselves. In the context of my own mental health, increasing my light sensitivity from antidepressants may have made daytime light more beneficial and may have reduced my rumination and negative self-talk.
What actually helps
Antidepressants have been life-changing for me, but I’ve learned they’re not the complete picture. Even on medication, my mental health is affected when I’m not keeping a regular sleep-wake schedule, like when I’m doing nights or working till late.
If I could go back to my 19-year-old self, I’d say two things:
1. Do all the sun-smart things, but spend as much time outside as you can ☀️
I remember being outside and thinking, “Wow, I feel so much better.” Brighter days provide a clear signal to your circadian rhythm that it is daytime and strengthens rhythms across the brain and body, which improves your mood, sleep, and health. Daytime lighting that you get outside (~100,000 lux) is much brighter than indoor office lighting (~500 lux). During the day, the more bright light you get the better.
Additionally, spending time outside is free! Eat outside, work outside, exercise outside. It also protects you (to some degree) from the adverse effects of light at night.
2. Don’t use bright lights after dark 🌃
Where possible, try to keep a regular sleep-wake schedule. But if you need to cram and stay up late, you can avoid some negative effects on your circadian rhythms by using a dim and warm lamp instead of bright overhead lights. All light after dark weakens rhythms across the brain and body.
Aim for something dim and warm. If anyone has a lamp, they want me to check, they can bring it into the lab and we can do some testing to see how bright it is and estimate the average effect on your sleep hormones. If interested get in contact with me at malisa.burge@flinders.edu.au
Also don’t ignore the bathroom lights. Especially if you are waking up in the middle of the night to use the bathroom. You may be inadvertently hitting your body at a time when it’s most sensitive to disrupting your circadian rhythms. If safe to do so, use a night light.
Get involved
If this resonates with you, there are ways to get involved in this research:
We’re running the Illuminate Study, looking at how the circadian system changes in response to antidepressants. We’re seeking people aged 18-40 with low mood. The study is ~10 weeks total, with two 3-night lab stays at Bedford Park where we assess markers of circadian rhythms, test individual light sensitivity, and complete cognitive tasks. Participants receive $2000 total compensation and a personalised report to understand their sleep and light patterns. You can find out more at: www.theilluminatestudy.com or express interest at: www.redcap.link/illuminate
We’re also building a stakeholder group of people with lived experience who want to help shape our research on light and mental health. If you’re interested in having input into the research questions we’re asking and how we measure these things experimentally get involved at: www.redcap.link/cmhgroup
And if you’re interested in conducting research please reach out (malisa.burge@flinders.edu.au)! There are opportunities for internships, honours projects, and PhD opportunities. My academic journey started off as an internship with Sean because I found his lectures interesting, and the research made such a compelling story. That started off with just a simple email.
You’d get to work with me and other post-docs, helping to run studies and data collection: screening people, completing consent meetings, having participants in the lab, collecting biological samples. We also have some pretty cool tech that’s been developed specifically for circadian research. If you’re in health, medical, psychology, or psychiatry, or if you’re interested in the biological and technological side from a physiology or biomedical engineering perspective, there are opportunities here.
The bottom line
I submitted my PhD thesis at 1:30am earlier this month (yes, I see the irony). But these days I’m much more careful about light. I keep more regular hours. I get outside during the day. I avoid using overhead lighting in the bathroom and bedroom after dark.
You don’t need to be perfect. But if you’re struggling, it might be worth considering whether your light patterns are working with you or against you.
