PQED consists of a
Brewster window (left) protecting the detector elements from impurities,
adjustable bellows
and the detector chamber itself. In order to further decrease uncertainties
in measurement,
the window was removed and the detector was protected from impurities
using nitrogen
flow.
The method helps discovering the most efficient lamps, which
may save billions in lighting costs in the future.
(September 18, 2015) Researchers
at Aalto University and VTT Technical Research Centre of Finland have succeeded
in developing a method which helps to improve the relative uncertainty in measuring
the luminous efficacy of LEDs from the approximate five percent of today to one
per cent in the future. The results were just published in the distinguished Light: Science & Applications journal.
– Thus far, solutions based on incandescent lamps have been
used in photometry, i.e. in measuring light detected by the human eye, explains
Tomi Pulli, a doctoral student at Aalto University.
– The photometers that lamp manufacturers use for
calibrating their devices have been produced and calibrated for incandescent
lamps, which results in errors when measuring the efficacy of LEDs. In our
research, we used a LED lamp with a well-defined spectrum and a PQED detector,
which we developed together with VTT MIKES Metrology and European partners, and
whose spectral responsivity can be determined highly accurately. Therefore, there was no need for the
problematic optical filters used in applications based on incandescent lamps.
Indeed, accurately determining and analysing the spectrum of the LED was the
most challenging and crucial part of the research, he reveals.