Page 63 - Energize June 2022

TECHNICAL

this type of equipment possible. Tuneable
lighting systems are available which provide
the full range of colour and intensity
controls. Two important parameters are
used when dealing with lighting technology:
colour temperature (CCT) and colour
rendering index (CRI).

Colour rendering index
The colour rendering index (CRI) is the
measurement of how colours appear under
a light source when compared with sunlight.
The index is measured from 0 to 100, with a
perfect 100 indicating that colours under the
Figure 2: Human circadian cycle (Panasonic) light source appear the same as they would
under natural sunlight.
In recent years evidence has accumulated for the presence of a non-visual photoreceptor
in the human eye, the primary purpose of which is to regulate the body’s internal clock. This Correlated colour temperature (CCT)
has begun to reveal the importance of exposure to adequate daylight levels for the health CCT is defined as the light emitted by a black
and wellbeing of humans, many of whom now spend most of their lives inside buildings. Light body radiator at different temperatures
sensitivity is controlled by rods and cones in the eye. Rods deal with low sensitivity and cones and is measured in degrees Kelvin (K).
deal with colour and higher sensitivity. The recently recognised third receptor – the intrinsically Paradoxically, lower colour temperature
photosensitive retinal ganglion cell – may provide an important means of linking health and (red / orange) light is described as “warm”
wellbeing to light. (for example 2200 K) and higher colour
Both the intensity and the spectral content of light can be used to stimulate or suppress temperature (blue / white) light is described
the secretion of melatonin and other hormones that in turn affect our mood and alertness, and as “cool” (for example 5000 K). Incandescent
control and contribute to the circadian cycle. Although the exact mechanisms and effects are not lamps are also black body radiators and
yet fully understood, this may be an important consideration for industrial and medical spaces as emit light at different colour temperatures
well as education, hospitality and even the home. depending on their intensity. Although
Circadian rhythms can be interrupted by our constant use of bright man-made lighting. neither fluorescent nor LEDs are black body
Disruptions in this rhythm can result in health issues such as obesity, cardiovascular and radiators, their light output is still referred to
neurological problems like sleep disorders, and can also affect work performance. as having a colour temperature.
Researchers have found that sources containing a high amount of blue light can disrupt CCT is usually visualised using a
the circadian rhythm. Brighter ‘cool’ lights cause alertness and wakefulness. Tuneable lighting chromaticity diagram which covers the
enables a return to the natural circadian rhythm by giving that range of lighting in either our colours visible to the human eye. Figure 3
homes or in the workplace. shows a colour temperature curve for an
incandescent lamp over different intensity
HCL technology values.
HCL aims to copy the natural changes in light that occur during the day, to synchronise with the Following the range of sunlight requires
natural human circadian rhythm. To do this requires a system that can follow the pattern shown that the CCT remains on the black body
in Figure 2 by changing both colour and intensity. Developments in LED lighting have made curve.

Figure 3: Lighting temperature scale (Lutron)

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