The document provides information on the Color Rendering Index (CRI) and Unified Glare Rating (UGR) for lighting. CRI measures a light source's ability to render colors accurately, with a scale from 0 to 100, while UGR assesses discomfort from glare on a scale from 5 to 40. Guidelines for acceptable UGR values are also outlined for different spaces to enhance visual comfort.

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EXPLAINING THE COLOR
RENDERING INDEX (CRI) AND
LEDS
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2. CRI, or the Color Rending Index, refers to the quantitative measure of
a light source’s ability to render known colors of materials as well as
objects. The process entails measuring the light emanating from a
test source and monitoring the appearance of re ected light as
compared to 8 known color samples. The CRI is usually rated on a
scale ranging from 0 to 100; the minimum index represents a light
whose colors aren’t distinct while the latter corresponds to daylight
or an ‘ideal’ white light.
Calculating CRI
The CRI of that particular source is calculated by measuring the
difference between the actual color & the known color. The nature of
the reference light source will also vary depending on the kind of light
source that’s being tested. When it comes to testing sources
featuring a correlated color temperature that’s less than 5000 0K
(degrees Kelvin), it’s advisable that a blackbody radiator is utilized as
the reference source. When dealing with test sources featuring a
higher CCT, you should use a spectrum of daylight as the reference
source. Regardless of the light source being tested, it’s always
important to pick the right reference source so as to retrieve accurate
CRI information from the sample colors.
For many decades, the Color Rending Index (CRI) scale has been
considered as an accurate measure of how effective lighting is in
reproducing expected colors through the spectrum. Regardless of
which lighting type is being utilized, it’s essential that you measure
the quantity of light before and after installation.
Uni ed Glare Rating (UGR) explained
Uni ed Glare Rating (abbreviated as UGR) is a measure of the
amount of discomfort emitted by luminaries using a psychometric-
based scale of discomfort. In other countries, UGR is used to
represent VCP (an abbreviation for visual comfort probability). Glare,
which can adversely affect your wellbeing as well as productivity at
work, is common in settings featuring several computer monitors.
The Uni ed Glare Rating starts from 5 and goes all the way to 40. The
lower numbers indicate less glare while the higher ones signify more
glare. The UGR is usually calculated using the following strict
formula:

3. Where,
Lb represents the background luminance in cd/m2
L represents the luminance of each part in the observer’s direction
eye (cd/m2);
w represents the solid angle of the luminous parts( i.e. of each
luminaire and it should be at the eye of the observer. It’s given in sr
r represents each luminaire’s Guth position index (i.e. the
displacement from the sight line)
Factors that affect the UGR value
When determining the Uni ed Glare Rating, factors such as
measurement point, re ection, the location, as well as the lighting
product operation are considered.
Quality classi cations

4. According to the UGR classi cation, there are 5 different quality
based classes. They include 16, 19, 22, 25 and 28. 28 represents the
maximum UGR value permissible in speci c spaces. It’s also
important to note that a luminaire featuring a UGR value of lower
than 10 results in zero glare.
Summary of UGR values
Technical drawing requires a UGR value of less than16
Of ces should have a UGR of less than 19
Reception areas should have a UGR value of less than 22
Archives, stairs as well as lifts should have a UGR value of less
than 25
Corridors and passageways should have a UGR value of less than
28
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