Phase advancing the circadian system with short pulses of blue light

Light in the morning is able to induce phase advances of the endogenous clock,
but optimal parameters about light duration, intensity and colour need to be
specified. No information is available about how short light pulses can be that
are still able to induce shifts. Available laboratory studies show that 6.5h of
light is capable of inducing shifts, and some information is available about
light pulses of 2 hours. In theory, a high intensity shorter light pulse in the
short-wavelength range should also be capable of inducing phase advances. In
addition optimal timing of the light pulse is important. In the laboratory we
are able to determine endogenous phase by measuring the melatonin rhythm. To
come to a practical measurement in the field, we will investigate other methods
to find out what best predicts endogenous phase.

Main objective of the study is to find out whether short duration pulses of
blue light at high intensity in the morning are capable of inducing a phase
advance of the circadian system.

In a randomized controlled, within-subjects, intervention study we will expose
people either to short duration blue light pulses or to longer duration blue
light pulses in the morning. During the control week the natural course of
endogenous circadian phase will be measured and compared with the pattern in
the experimental weeks.

All subjects will participate in all conditions. Subjects are housed during one
night in our facility to perform baseline measurements. During the rest of the
time they perform the measurements at home. During the timing of saliva
collection they should obey to instructions about their environmental light
exposure (dim light) and their food and drinks intake. They receive
instructions on a window where sleep is allowed. Nature and extent of the
burden per subject are minimal and there are no real risks associated with
participation. The major concern in these types of studies is the ocular safety
of using a blue light emitting lamp. To verify the safety of the used light
source the device was submitted for Ocular Radiation Hazard testing by the
Commission International de l*Eclairage (CIE). The device was determined to be
safe with even at a factor of 100 times the normal usage recommendations. The
subjects may slightly benefit from the treatment by obtaining a phase advance
of their circadian system. The benefits for science and clinical practice in
the future are large and make this study innovative and exciting.