Equipment: Lamps and Gear - Road Lighting: Fundamentals, Technology and Application - page 111

Table 10.1 Some of the more important characteristics of lamps
Luminous efficacy (lm/W) Shape and dimensions

Lumen package (lm) Run-up time (min)

Lamp price Re-ignition time (min)

Lifetime (h) Dimmable yes/no

Correlated colour temperature (T k ) Burning position

Colour rendering (R a ) Ambient temperature sensitivity

S/P ratio Brightness

Lamp-lumen depreciation Environmentally-unfriendly materials

10.1 Performance Characteristics

10.1.1 Survey of Lamp Properties

There are a great number of different lamp types. The reason for this is that the ideal
lamp simply does not exist. A lamp that is suitable for one situation may be totally
unsuited for another. Each lighting application calls for a lamp with a specific set of
properties. Table 10.1 provides a list of some of the more important lamp properties,
which can vary with different lamp types. It is the task of the lighting designer to
choose the lamp properties best suited to a particular application.
Table 10.2 gives a survey of the more important characteristics of the different
lamps used in road lighting. The values given include the effect of the electrical gear,
and are representative for the wattage versions commonly employed in road lighting.

10.1.2 System Efficacy

The measure of energy efficiency as far as lamps is concerned is the luminous efficacy
expressed in lumens per watt. Apart from the lamp itself, the electrical gear, in
particular the ballast for gas discharge lamps and the driver for solid state lamps also
consume energy, so it is important to always include the ballast and driver losses in
lm/W figures to give the so-called system lm/W figures. This, of course, has been
done in Table 10.2 as will be done everywhere in this topic.
From the standardized eye-sensitivity curve, V(

), as given in Fig. 6.2, it directly
follows that the theoretical maximum luminous efficacy of a hypothetical, ideal,
lamp that produces electromagnetic radiation without energy losses and with a sin-
gle wavelength for which the eye has its maximum sensitivity (i.e. 555 nm) is 683
lm/W. This theoretical maximum is valid for monochromatic light. The theoretical
maximum efficacy of a lamp producing white light is not as clearly defined, because
it is dependent on the quality of the white light being considered. With a hypotheti-
cal, ideal light source of reasonable-to-good white colour quality, in which again all

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