Equipment: Luminaires - Road Lighting: Fundamentals, Technology and Application - page 151

Table 11.2 CIE luminous
intensity classes. (CIE 2010 )

I max (cd/1000 lm) at and above
70 ⓦ

80 ⓦ 90 ⓦ 95 ⓦ

G4 500 100 10 1

G5 350 100 10 1

G6 350 100 1 1

The beam spread is an important characteristic of the light distribution of flood-
lights. It is defined as the angle, in a plane through the beam axis (direction of
maximum intensity), over which the luminous intensity drops to 50 % of its peak
value. To provide extra information on the beam characteristics, the beam spread for
another percentage (for example 10 %) is sometimes stated as well.

11.1.2 Luminaire Classification

The luminaires employed in road lighting can be divided into three basic types:
conventional road-lighting luminaires that throw the main part of their light along
the road, rotationally-symmetrical luminaires, and floodlights with relatively nar-
row beams (one exception is the catenary type of luminaire that will be described
in Sect. 13.1.8). While the CIE and the European Standard classify light distribu-
tions only according to their glare aspect, IESNA in North America classifies light
distributions based on many more aspects.
CIE ( 2010 ) classifies luminaires into six luminous-intensity classes G1-G6 ac-
cording to the luminous intensities per 1000 lamp lumen for the angles of elevation
70, 80 and 90 ⓦ and for the area above 90 ⓦ . Table 11.2 shows the requirements for the
three most stringent classes. The European Standard uses the same classes.
IES defines a luminaire classification system (LCS) based on the lumen distribu-
tion within solid-angle areas (IES 2007 ). It replaces the previously used full-cutoff,
cutoff, semi-cutoff and non-cutoff system. The LCS system divides the light
distribution of a luminaire into three zones (Fig. 11.4 ):
• the back-light quarter sphere, denoted by the letter B,

• the up-light hemisphere, denoted by the letter U,

• the forward-light quarter sphere, denoted by the letter F, responsible for the light-

ing of the area to be lit. The higher elevation angles in this quarter sphere are also
responsible for possible glare to road users outside the area, which is the reason
why this zone is also denoted by the letter G.

Each zone is divided into solid-angle subzones denoted by low (L), mid (M), high
(H) and very high(VH). Depending on the total luminous flux radiated in each of
the solid angles of a subzone, the luminaire is classified into one of six back-light
classes (B0-B5), and one of six up light classes (U0-U5) and finally one of six
forward-classes expressed as glare classes G0-G5. The classification system, with