Light Reflectancy Tile 101

8/12/2019 Light Reflectancy Tile 101

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Tile 101 Light ReflectancyBy Kristen Radtke

ight reflectancy has been a recent topic of

conversation and how it relates to interior finishes;

specifically floor tile. Tile in the past was not tested

for Light Reflectance Value (LRV). Why then is the

question being asked?

Our standards for buildings, interiors, and finishes

are important. Not just for health, safety and

welfare of the occupants, but as a valuable

consideration for the environmental implications of

the interiors and the finishes applied. The question

dealing with Light Reflectancy is due to the interior

environment, but also for the solar implications.The sustainability and green qualities in our

architecture are just as important, if not for the

green-ness of it, then for the green-ness of the

bottom line. If it saves energy it should save

money.

Value in dealing with color is often confused with

the term intensity. Intensity deals with the

brightness or dullness of a color; how clear or

muted a color is. Value is an important term as it

speaks strictly to the lightness or darkness of a

color. LRV is the total quantity of useable and

visible light reflected by a surface in all directions

and at all wavelengths when illuminated by a light

source. It is a measurement that indicates how

much light a color reflects, and how much it

absorbs. This measurement is quantified as a

number based on a scale of 0 100; zero is

absolute black and 100 is pure white. Every color

reflects a certain amount of light while absorbing

the rest as heat energy. Dark colors with low lightreflectance values tend to reflect little light while

absorbing lots of heat energy. Conversely, light

colors with high reflectance values reflect a lot of

light and absorb little energy. When designing a

space to take advantage of heating and cooling a

building, these basics are important. For LEED

structures, utilizing the most natural light in an

interior is the goal. By utilizing natural light, there is

less energy spent on lighting costs, as well as

cooling costs to keep the space at a comfortable

temperature.

DAY LIGHTING

The sun provides several different wavelengths of

UV light that emit toward the earth. What does

reach us on earth is about 5% UV light with

wavelengths between 280-400 nm, 50% of visible

light between 400-780 nm and 45% of infra-red (o

heat) ranging from 780-2,500 mm. All of these

waves interact with the substrates they fall on

either being absorbed, transmitted or reflected. Al

absorbed energy eventually gets converted to a

longer wavelength creating heat.

To take advantage of the most day lighting, the

interior LRV would reflect light and heat, instead of

absorbing the light and heat. In this situation

lighter is better. Day lighting reduces the need fo

electrical lighting of building interiors, resulting indecreased energy use. A well-designed day-li

building is estimated to reduce lighting energy use

by 50 60% (Sustainable Building Technica

manual). This conserves natural resources and

reduces air pollution due to energy production and

consumption.

Figure1: UVLightSpec


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Day lighting design involves a careful balance of

heat gain and loss, glare control, visual quality and

variations in daylight availability. Shading devices,

light shelves, courtyards, atriums and window

glazing are all strategies employed in day lighting

design. Other important considerations include the

buildings orientation, window size and spacing,

glass selection, reflectance of interior finishes and

locations of interior walls. Research on day-lit

spaces shows an increase in occupant productivity

and reduced absenteeism and illness.

As related to day lighting and design standards -

photo-responsive controls for electric lighting can

be incorporated into day lighting strategies to

maintain consistent light levels and to minimize

occupant perception of the transition from natural

light to artificial light. These controls result in

energy savings by reducing electric lighting in highdaylight conditions while preserving foot candle

levels on the task surface. (def.: footcandle is

defined as a unit of measure of the intensity of light

falling on a surface, equal to one lumen per square

foot. Originally this was defined with reference to a

standardized candle burning at one foot from a

given surface.)

Optimized Energy Performance is one criterion for

LEED projects, or designing toward LEED that

takes day lighting into effect. How does the light

reflectance of the floor area affect the room's

interior? Brightness and quality of light are an

important role in the illumination of institutional,

commercial and industrial facilities. The light

reflectivity ratings for floors are important when

taking the complete interior environment into

consideration. Since some flooring materials are

made of combinations of different colors, measured

light reflectance value is an average value based

on a large area of the pattern. (Light reflectivity

values are determined by measuring thepercentage of light directed at any surface that is

then reflected under standardized test conditions.)The Illuminating Engineering Society of North

America recommends that floors have a reflectance

factor of 20% to 40% for optimal sight in offices.

Adequate visual contrast is provided if the Light

Reflectance Values (LRV) of the contrasting areas

differ by at least 30 points. Contrast is a calculation

of the difference between the LRV between the

foreground color and the background color.

COLOR AND LIGHT REFLECTANCY

The CIE color model was created by the

International Commission on Illumination known as

the Commission Internationale de lElcairage (CIE)

in 1931. The CIE color model is a mapping system

that uses tristimulus (a combination of 3 color

values that are close to Red/Green/Blue) values

which are plotted on a 3D space. The CIE

specification is supposed to be able to accurately

represent every single color the human eye can

perceive. The CIE color models uses an XYZ axis

of a three dimensional model. The Y parameter is

a measure of the brightness of a color, the X

measures the chromaticity of a color, and the Zparameter is [1-x-y]. All three create the tri

stimulus of a color. The human eye detects the

presence of different wavelengths and senses them

as a distinct color. If a substrate absorbs all visible

light falling onto the eye, it sees this surface as

black, and if the surface reflects all light, it sees

white.

Figure2:CEIColorModel

Figure3:CEIColorModel


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LRV is dependent on the saturation of the color and

the amount of white or black that color contains. It

is virtually impossible to have a dark color with a

high LRV or a pastel shade with a low LRV. The

LRV of the same shade can be affected by the

surface of the substrate. A glossy paint, even a jet

black glossy paint will have some reflectance from

the surface. Flat and textured surfaces do not have

this property and reflect only in a diffused manner.

Higher LRVs are often specified for building

systems which may be sensitive to heat. This

recognizes that absorbed light will convert to heat

but does not necessarily take into account the 45%

of the sun's energy emitted in the infra-red range.

TESTING

Testing for LRV is measured with color

measurement equipment, specifically a

spectrophotometer. The value of the LRV is ameasured result for each color. The

spectrophotometer will measure a Y value which

is equal to one of the three CIE tristimulus values

and essentially measures the luminous reflectance

(LRV) or transmittance (absorption) of a color. The

Y value is used to determine the Contrast Ratio

between two colors. Y = Brightness. This test does

not produce, pass or fail results. A scale of results

varies from 0 to 100; most finishes fall within the

range of 5% - 85%. We can easily measure the Y

value and therefore obtain LRV values for any of

our finishes.

ASTM testing for Tile: ASTM C609 07 Standard

Test method for Measurement of Light Reflectance

Value and Small color differences between pieces

of ceramic tile.

This test method covers the measurement of Light

Reflectance Value (LRV) and visually small color

difference between pieces of glazed or unglazed

ceramic tile, using any spectrophotometer tha

meets the requirements specified in the test

method. LRV and the magnitude and direction of

the color difference are expressed numerically, with

sufficient accuracy for use in product specification

LRV may be measured for either solid-colored tile

or tile having a multicolored, speckled, or textured

surface. For tile that is multi-colored, an average

reading should be obtained from multiple

measurements taken in a pattern representative of

the overall sample. Small color difference between

tiles should only be measured for solid-color tiles.

How does one figure out what the light reflectancy

is for a tile? Testing for tile can be submitted to the

TCNA (Tile Council of North America). For this

test, one must submit 80 tiles (4 x 4 size) for the

ASTM C- 609 Measurement of Light ReflectanceValue and Small color Differences.

A low tech option we have used is to obtain a pain

fan deck and match the paint color chip to the tile.

The LRV is noted on the back of the paint chip as

the results of the test for the solid paint color. This

is one way to get a feel for where the tile will rate in

the more scientific testing. The TCNA test would

be required for LEED certification, or othe

accreditation.

As our buildings become more sophisticated, so do

the materials, and the testing of the materials tha

are installed and applied into our livable and

workable spaces. Day lighting concepts when

applied correctly can save energy, money and

create less pollution. Who knew day lighting also

led to less absenteeism and illness?.My office

needs a window!

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Light Reflectancy Tile 101