8/12/2019 509 Light Planning en 12464-1

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Glare

Glare occurs when part of an interior space is significantly brighter

than the rooms luminosity. In these instances the eyes are exposed

to a more intense light than they are normally adapted to. The most

common cause of glare occurs when the luminaire and window can

be seen directly or via reflections, within the normal field of vision.

Elderly people are usually more irritated by glare than young people.

This is mainly due to the increased clouding of the eyes lens experi-

enced with age as well as a reduction in the ability to adapt.

Glare can be divided into two different types; disability glare and

discomfort glare.

Sight impairment glare and discomfort glare can occur simulta-

neously or separately.

Light planningEN 12464-1

Lowest shielding angle for the light sources luminance

Light sources luminance [kcd/m] Minimum shielding angle

20 to < 50 15

50 to < 500 20

500 30

The values in the table do not include indirect luminaires or luminaires that areinstalled below normal eye level.

Calculation of the glare indexThe degree of discomfort glare for indoor installations can be esti-

mated by calculating the glare index according to the UGR method.

The method will, through the introduction of the new standard

EN 12464-1, replace the previous European calculation method

(NB-method). The demands on the glare index documented in

EN 12464-1 refer to the highest average value for the lighting. The

UGR-method (Unified Glare Rating) is described in CIEs publication

no 117-1995.

The UGR glare index for discomfort glare is ranked on a scale,

which in practice runs from 13 to 28 where the higher the glare

index the higher the level of glare. The smallest change in the glare

index denoting a significant difference is 3.

The glare number should be calculated according to the table

method to check whether the recommended glare index in the

standards tables is met by a specific lighting installation. (The

method is described in CIEs publication no 117-1995). However, this

method assumes that the luminaires in the room are positioned

symmetrically and feature symmetrical light distribution across and

along the luminaire.

Luminaire manufacturers provide information/table data as a

part of the luminaires photometric data to calculate the lighting

installations glare index.

Disability glareDisability glare usually occurs when an object in the vicinity of the

normal line of sight, has a significantly higher luminosity or lumi-

nance than that which usually occurs in the field of vision. If an eye

is exposed to a continuous intense light, the eyes adaptation can be

affected negatively and cause deterioration in visibility, or what is

known as contrast reduction.

This contrast reduction can be sufficient to make words and

images barely visible and in doing so make it difficult to carry out

the visual task. Alternatively, if the light source causing the glare is

directly in the line of sight this can cause noticeable after-images.

The most common source of sight impairment glare internally, is

the sun and sky viewed from a window or a badly shielded light

source observed directly or via reflection.

Disability glare should therefore be prevented through using

luminaires that effectively shield the light source (see table).

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