Light-Pollution Parameters - Road Lighting: Fundamentals, Technology and Application - page 238

Fig. 16.2 The actual situation
and the hypothetical ideal
situation that are compared in
the definition of upper flux
ratio UFR

Actual

ˁ suround ˁ suround

ˁ area

Ideal

ˁ suround ˁ suround

ˁ area

of the lighted area and its surroundings according to the formula (AFNOR 2011 ):

1 DLOR

E av,initial
E av,maint

ULOR
ˁ area ∗

ˁ surrounds
ˁ area

− μ

UFR = +

μ + μ

where:

E av,initial = The initial average illuminance of the area to be lit,

E av,maint = The required maintained illuminance of the area to be lit,

ULOR = Proportion of the upward flux to the total flux of the luminaires in their

installed position,

DLOR = Proportion of the downward flux to the total flux of the luminaires in

their installed position,

ˁ area = Reflectance of the area to be lit,

ˁ surrounds = Reflectance of the surrounding surfaces,

μ = Utilization factor of the installation related to the area to be lit.

In the case of road-lighting installations designed on the basis of luminances, the
illuminance ratio in the formula has to be replaced by the luminance ratio. That the
ratio of initial to required maintained lighting level plays a role in the value of UFR
is in fact an impulse to design an installation as close as possible to the required
lighting level: needless over-lighting automatically results in a higher and therefore
worse value of UFR.
At first glance it may appear strange that the reflectance of the area to be lighted,
ˁ area , is in the denominator of the formula. The higher the value of this reflectance, the