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ART AND SCIENCE OF ILLUMINATION FROM LEDS .pdf


Original filename: ART AND SCIENCE OF ILLUMINATION FROM LEDS.pdf
Author: Lionel Barden

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ART AND SCIENCE OF ILLUMINATION FROM LEDS

Everybody in business must realise by now LED lighting provides a huge opportunity for dramatically
reducing energy use and in turn the energy cost, but it can do so much more in performance to
further reduce energy use.
Every traditional lamp (other than LED) produces light in all directions. The performance of this
lighting is based, not only on the lumen output, but also on the capability and quality of the
luminaire reflector and/or lens. This essentially means the performance of these lamps is based on
the light output ratio of the luminaire i.e. the usable light directed from the luminaire.
Depending on the light source e.g. fluorescent or mercury vapour lamps this can be as low as 50%
i.e. the luminaire only provides 50% of lamp light where it is required. If a fluorescent lamp provides
70 lumens per watt this means that the luminaire is producing 35 usable lumens per watt. Then add
to that a depreciation factor of 30% over life.
LEDs produce mono directional lighting. This means that all of the light is going in the direction
required. The luminaire only has to control the beam pattern to provide the required effect. This can
be done in three ways, by reflection, by refraction and by diffusion. Reflection and refraction are the
two highest performance methods both for accuracy as well as for maximising light output.

Porsche Museum
using low brightness
reflector fittings with
light output around
95% mark.

Reflection and refraction methods of control are so much more efficient with LEDs than they were
with traditional lamps as is colour rendering and colour choice and can produce quality light from
low brightness luminaires illuminating the task as required.
Diffusion is the lowest performer. An opal diffuser throws light in all directions but can reduce the
lumen output by as much as 40%. Why start with high lumen values, say 130 lumens per watt, then
cut that back to 80 lumens per watt and spray the light everywhere, depreciating the performance
of the LEDs.
Yet today in a large number of LED
lighting installations we see LED
luminaires with opal diffusers. There
is also a huge number of traditional
lamp replacements using LED
replications.

The most common of these is the fluorescent lamp replica.
Again, why reduce the LED performance by diffusion to effectively give off light in all directions and
then try to reflect this light by the original luminaire to where it was aimed at in the first place.
Add to this the fact that it is fitted into existing lamp holders. Any installation is only as good as the
weakest point and used lamp holders are the weakest.
LEDs require heatsinking for long life performance. Heatsinks operate by transferring heat to lower
temperature air. When the air temperature inside the sealed tube of these replicas reaches the heat
sink temperature, the heat sink is no longer affective.
(There have been many recalls of these lamps due to danger of heat. As an example, four of these
recalls totalling 1,408,000 lamps were from major international brands including Cree, Osram and
Phillips.)
LED lighting is a sensational technical product that is creating a revolution in the lighting industry but
still requires further promotion and education to lift demand in the retrofit market. Technical design
knowledge and strength in the “Art and Science” of illumination will provide much greater savings in
the energy use and should be advocated to the commercial consumer.
It’s not rocket science.
Lionel Barden
Managing Director
Eco Energy Group Ltd.


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