Architects memo no. 111: May 2013
We were recently approached to see if we could provide ‘glare’ measurements for our paints and colours, which led to a little head scratching trying to define exactly what was being asked of us.
For the most part, glare seems to be a comparative
phenomenon. A bright oncoming full-beam headlight coming
at you suddenly when driving at night along a country road; irises having fully dilated your eye pupils to maximise what
little light was previously available, will certainly cause
The exact same light, coming at you in full daylight; pupils
fully contracted, will go past scarcely noticed. Similarly, a
single white house on a bush clad hill will stand out like a
sore thumb while the same dwelling in a ‘pueblo blanco’
would be part of the background, with potted greenery and
flowers providing the visual ‘stand out’.
The most useful data that we can supply are ‘light reflectance
values’ (LRV) but, it must be admitted, these do not tell the
I am reminded of a neighbourhood dispute in a very high
class hill suburb. The neighbour higher up the hill complained
vociferously that, at certain times of day, the sunlight reflecting
off the lower neighbour’s unpainted galvanised roof caused
intolerable ‘glare’. The lower neighbour was instructed to
paint their roof a dark colour with a LRV of less than 5. This
the lower neighbour duly did, but, as the restriction was only
the colour, he used a typical durable gloss roof paint. At those
times of day the ‘glare’ problem was exacerbated!
Paints reflect (reflect is used here to include reflection,
refraction and diffraction) in two ways - specularly (or mirror
like) and diffusely. Similar to the example described above,
a high gloss black paint can reflect enormous amounts of
light but one has to be opposite the light source to perceive
this. The amount of specularly reflected light is such that the
underlying colour becomes indistinguishable.
A flat, white paint also reflects an enormous amount of light
but does so diffusely. A gloss paint provides a smooth surface
while, to a photon of light, a flat paint is like a boulder strewn
beach from which it will bounce in totally unpredictable
angles. From whichever angle one views such paint, it will
be uniformly bright but without the intense glare one can
experience ‘downside’ of a glossy paint.
There is another intensification of reflected light as exhibited by
fluorescent paints and those containing ‘optical brighteners’.
These products have the ability to absorb some of the ultra
violet light spectrum and emit it as longer wavelength, violet/
blue wave light. The eye is very sensitive to these wavelengths
and perceives them as being somewhat ‘glary’.
Your scribe has an idiosyncratic (and somewhat embarrassing)
method of measuring glare. When stuck in front of bright
paints in full sunshine I sneeze - many times. Repeated
applications to the International Standards Association failed
to convince them as to the relevance of the ‘ATISHOO’ scale of
LRV demands of various bodies can bring conflict which can
be difficult to resolve. Councils applying covenants to paint
colours used on buildings erected in bush clad suburbs may
demand a LRV of less than 50% in order to manage the
aesthetics of a development. Suppliers of several building
systems and elements however, are cautious about the effect
of the excess heat that may be absorbed and specify an LRV of
not less than 40% - hence the dilemma.
The paint industry does offer a path forward through the use of
infra-red reflecting pigments (such as Resene CoolColour™) but
the conversation has yet to be had that will provide a facile
framework for their specification.
While an LRV value is a useful indicator for the visual ‘glare’
properties of a colour, Total Solar Reflectance (TSR) is more
useful to achieve a picture of the thermal stress a colour may
inflict. A better specification for a covenanted colour could
read: 60% gloss - not more than 10%; LRV - not less than 50%;
TSR - not less than 40%. Glaringly obvious? Not quite - but
something to work on.
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