semi-rigid rubber quarter sphere with a flattened
outer lip on one edge, which facilitated attachment
to the mask. The lip was sewn onto a semi-rigid half
ring of leather, which was then sewn to the rim of the
eye opening of the mask. The inner surface of the cup
was covered with reflective aluminium foil tape. The
LED was positioned inside the cup at the centre point,
where the lip met the rim of the eye opening. The legs
of the LED pierced the eye cup and were soldered to
the electrical wires outside the eye cup within the
neoprene sleeve. The LED was positioned to shine up
onto the reflective foil surface, diffusing light onto
the horse’s cornea.
This provided uniform, diffuse light and minimised
distraction to the horse, permitting maintenance
of normal behaviour. A 3 cm diameter hole was
cut through the cup 1 cm below the LED to permit
peripheral vision on the right side.
The LED used was a Kingbright 7.6 °— 7.6 mm Super
Flux LED Lamp L-7676CQBC-D Blued. It has a luminous
intensity of 1300 millicandelas when powered by
a current of 70 mA. The peak wavelength was 468
nm, which is within the desired range for optimum
suppression of melatonin in mammals. The spectral
line half width was 25 nm, providing a broad margin
for error in terms of the efficacy of the wavelength.
The beam angle of the LED was 70° allowing for
some degree of movement between the LED and the
horse’s eye. Each mask was individually calibrated
using different levels of resistance to provide 50
Lux of diffuse light to the horse’s eye. The Lux levels
(illuminances) for each individual mask were adjusted
and measured using a Lux meter (LX-1010 B Digital
Lux Meter).
Each mask used 4 Duracell Pro-cell AA sized 1.5 V
batteries (replaced at 2-week interval) and powered
a circuit containing an Arduinoe board, a switch (on/
off), a clock and a set of resistors. The Arduino board
was programmed to turn the LED on at 16.30 h each
day and switch it off at 23.00 h every night. A resistor
was connected in series with the LED to determine
the current flowthat produced illuminance of 50
Lux. In order to save power and prolong the battery
lifetime, much of the Arduino functionality was put
in a sleep mode. The circuit also included a real time
clock module that kept time so that the Arduino could
power the LED for specific intervals. The real time
clock had its own small, independent battery so that it
did not lose time when the switch for the main circuit
was turned off.
Experimental protocol
Beginning on 1 December, Group 1 received light
therapy via artificial lighting indoors in individual
stalls. The lights, which provided 250 Lux of light to
each mare at eye level, were switched on at 16.30 h
every day and remained on until 23.00 h each night.
Also beginning on 1 December, Group 2 received
individual light therapy from head worn masks that
provided 50 Lux of blue light to the right eye of each
mare. The mask light turned on automatically at 16.30
h each day and turned off at 23.00 h every night.
Group 3 served as a control group and received no
artificial light therapy, but was exposed to the natural
environmental light/dark cycles for the duration of
the experiment.
Beginning on 20 November and continuing at 2-week
intervals throughout the experiment the mares
underwent transrectal ultrasound examination and
jugular venipuncture. Ovarian activity in terms of
follicle number and size, presence or absence of
corpora lutea, cervical tone and presence or absence
of uterine oedema were recorded for each mare at
every ultrasound examination and the blood samples
were assayed to establish circulating progesterone
concentrations. Oestrous cyclicity was defined as the
presence of follicles >20 mm and the confirmation of an
ovulation determined by the presence of a previously
unrecorded corpus luteum or corpus haemorrhagica
on an ovary in conjunction with progesterone levels
>1 ng/ml. Transitional phase was defined as follicles
>20 mm and associated physiological characteristics
typical of oestrous activity but in the absence of
progesterone levels indicative of ovulation.
Fig 1: A horse wearing the light mask that provided 50
lux blue light to the right eye. The light mask consists
of a leather headpiece with a semi-rigid rubber cup
containing a single blue-light emitting diode fitted
on the inside of the rubber eye cup. The inner surface
of the cup is covered with reflective aluminium foil to
reflect li