Equipment: Lamps and Gear - Road Lighting: Fundamentals, Technology and Application - page 136

100

828 840

80

60

40

20

0

400 450 500 550 600 650 700 400 450 500 550 600 650 700

ʻ (nm) ʻ (nm)

Fig. 10.23 Spectral power distribution of a phosphor LED with colour designation 828 (T k = 2800
K, R a = 80, S/P ratio = 1.2) and 840 (T k = 4000 K, R a = 65, S/P ratio = 1.4) respectively

Fig. 10.24 White-light
efficacy projections for
commercial LED packages.
Warm-white: T k between
2600 and 3700 K with
R a > 80; cool to bluish white
T k between 4800 and 7000 K
with R a > 70

200

cool-white

lm/W

150

warm-white

100

50

0
2005

2010 2015 2020 2025

Higher-power LEDs have higher efficacies, while those with better colour rendering
have lower efficacies. Today, cool-white LEDs are commercially available in effica-
cies of around 150 lm/W, and warm-white LEDs with colour-rendering indices of
around 80 with efficacies of around 120 lm/W. These lm/W values include driver
losses and do not take into account losses in secondary optics. Further improvements
may be expected. The US department of energy (DOE) made future projections
through a collaborative effort between industry, academia, research, laboratories
and the US government (DOE 2013a ). These projections, until the year 2025, are
shown in Fig. 10.24 for two groups of phosphor LEDs. The ultimate phosphor LED
efficacy according to this projection is about 200 lm/W.

Lifetime LED light sources have a lifetime, based on L 80 , of between 50,000 and
100,000 h. As has been discussed, the actual lifetime is very much dependent on the
chip's junction temperature under operating conditions. Retrofit LED bulbs, with
their limited space for heat dissipation, have a lifetime of some 25,000-35,000 h.

Run-Up and Re-ignition LEDs give their full light output immediately after switch-

on and after re-ignition.