1. Using light to tell time of day Tim Brown University of Manchester
Why is this important?
What are the underlying biological mechanisms?
Using light to tell time of day Tim Brown University of Manchester

2. Daily variations in physiology and behaviour are an integral part of life
X 1 Billion
(109)
Light is the key environmental signal that regulates the clock
Clocks regulate the physiology/behaviour
of virtually all organisms
Effects of ‘artificial’
light?

3. The body clock regulates every aspect of human physiology
Goel et al. 2013; Coldwells et al. 1994; Dijk and Czeisler, 1994

4. The body clock adjusts slowly to changes in the environment
Goel et al. 2013; Coldwells et al. 1994; Dijk and Czeisler, 1994

5. Why is it useful to understand how the body clock determines time of day?
Regular travellers
Shift workers
Young people
The elderly and
chronically/
critically ill
~20%
workforce on rotating shifts with night work
~20%
UK population at school/university age
17.5%
UK population
over 65

6. Body clock & shift work:
The Body clock
Cant keep up with rotating shift work

7. Body clock & shift work:
Implications for
Health and safety
~2x greater risk of accident or injury during night work
Chernobyl
Ukraine
Three Mile Island
PA, USA
~50% increased risk of type II diabetes
~30% increased risk of colorectal cancer
~20% increased risk of breast cancer
With 10 or more years shift work
Pan et al. 2011; Wang et al 2015; He et al 2015
Hobbs et al 2010; Wagstaff and Sigstad 2011

8. Biological time changes with age
male
female
Body clock is shifted later in teenagers
Time of mid-sleep
10% lower university grades during morning tests
Roenneberg et al. 2003; 2007; Harazsti et al 2014

9. The biological clock weakens in the eldery
Healthy adult
Body clock function is impaired in:
The elderly
Neurodegenerative disorders
Chronic and critically ill patients
Light exposure is insufficient to support
normal body rhythms:
Limited access to natural daylight
(elderly/institutionalised)
Environments with constant illumination
(hospital/intensive care)
dementia patients
+ brighter lighting
dementia
patients
van Someren et al. 1997

10. SUMMARY I
The body clock is an important determinant of health and well-being throughout daily life
Light is a key environmental factor that adjusts internal timing
Ways of manipulating light exposure to better align the clock with our daily schedules could be beneficial to many groups in society

11. The brain’s ‘master’ clock: The suprachiasmatic nucleus (SCN)
DAY
NIGHT
Mouse SCN
Spontaneous activity
in vitro;
Brown et al. 2006
Spikes/s
1. The SCN is provides time-of-day information to the rest of the brain and body
Time of day (h)
2. The eyes signal directly to the SCN
Mouse SCN light response in vivo;
Brown et al. 2011

12. How does the clock use light to tell time of day?
2. The clock’s response to light is proportional to the amount detected
1. The clock is maximally sensitive to light at dawn and dusk

13. Circadian responses to light survive total outer retinal degeneration
What tells the clock how bright the world is ?
Circadian responses to light survive total outer retinal degeneration
Berson et al. 2002; Science
SCN-projecting RGCs are intrinsically light-sensitive
Rod
cell
Cone
Retinal
ganglion
Cells
(RGCs)
Melanopsin accounts for intrinsic light response
SCN
Melanopsin knockout RGC
Hattar et al. 2002, Science; Lucas et al. 2003, Science
Freedman et al. 1999, Science
Lucas et al. 1999, Science

14. Why is melanopsin significant?

15. Circadian and perceived brightness are not equivalent
New smart LED lighting systems allow for much greater control over the circadian effects of light without compromising perceived colour or brightness

16. Applications of circadian-directed lighting
Regular travellers
Shift workers
Young people
The elderly and
chronically/
critically ill
Maximise melanopic brightness at the start of the ‘day’
Minimise melanopic brightness at the end of ‘day’
Where constant illumination is required –
provide a circadian (melanopic) brightness cycle

17. Cones can also influence the body clock!
The colour of natural light changes during twilight
Clouds change the amount of light present during twilight…..
but NOT its colour
Melanopsin cells receive
signals from cones
Measuring colour helps the clock tell time of day !!

18. Colour can dramatically alter biological timing in mice

19. IMPLICATIONS: 1) Adjust melanopsin activation 2) Alter colour
There are potentially two ways to adjust how artificial lighting affects our body rhythms:
1) Adjust melanopsin activation
2) Alter colour