Equipment: Lamps and Gear - Road Lighting: Fundamentals, Technology and Application - page 134

Fig. 10.21 Phosphor
suspended in silicon
encapsulation ( top ) and
conformal phosphor coating
( bottom )

Silico n
enca psulation
Phosphors

Phosphors

LED chip

Fig. 10.22 Principle of a
remote-phosphor LED
module creating white light

blue LEDs

blue light

phosphor

white light

LED Cluster The luminous flux of one individual LED is quite low compared to that
of gas-discharge lamps. Multiple LEDs are therefore often mounted on a printed-
circuit board (PCB) to obtain a LED module emitting a high luminous flux. The
PCB establishes the electrical connections between all components and the external
electrical driver. The PCB must also conduct away the heat from the heat sinks of
the individual LEDs to the outside world.

LED Module LED modules integrate the LED cluster with the electric driver,
the mechanical connections and with the secondary optics that determine the light
distribution of the module.
Some LED modules make use of the so-called remote-phosphor technology
(Fig. 10.22 ). Here, a number of blue LEDs are placed inside a mixing chamber
of high and diffuse reflective material. The phosphor layer, positioned remotely
from the LEDs on the bottom of the chamber, converts the blue light of the chips
into white light. In this way, thanks to the mixing process, small differences in light
output and or colour of individual chips are not visible. The risk of disturbing glare is
also reduced because the luminance of the large-sized phosphor layer is much lower
than the luminances of small, individual LEDs.
For users it can be important to have LED modules (also called LED engines) that,
as with most conventional lamps are interchangeable with products from different
manufacturers. Interchangeability is achieved by specifications produced by Zhaga, a
global industry-wide organisation (Zhaga 2013 ). The specified interfaces for physical