Date: Fri, 14 Jan 2000 10:09:49 +0200 From: Juerg Steiger <juerg.steiger@iae.unibe.ch> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg120$foo@default> Subject: Re: Light meter
Hi Zachari
1 lux is defined as the light energy received on 1 squaremeter from a
light source of 1 lumen.
For German speaking CPers a good survey on 'Lichttechnische Grundbegriffe'
is available on
http://www.osram.de/produkte/lichtplanung/lichttechnisch.htm
For English speaking people search at http://www.osram.com or other
manufacturers of light sources.
Light meters measure only the total light energy received from a light
source but not the relative spectrum distribution of the light source.
Human eyes have their highest light sensititvity at a wave lenght of about
550 nanometer, while plants have 2 biologically important peaks around
440nm and again at 650 nm. Therefore for plant growth the spectral
distribution of the light source is important. Pleasant light for our eyes
may not automatically be suitable for plants. Graphs with the emitted
spectrum of different light sources are available by their manufacturers.
ATTENTION!! For industrial plant production different light sources are
available with particular spectrum peaks enhancing plants growth. But
industrial plant production usually deals with ANNUAL plants producing one
or more plant generations per year. After the flower or fruit period the
plants perish and are disposed. For many PERENNIAL species these
plant-specific light sources increase leaf growth and flowering/fruiting to
fast, resulting in disturbing the internal watch of the annual growth cycle
which is genetically anchored. The results are to early metamorphosis into
the winter stage (or from winter to summer stage) and increased microbial
infestations. For perennials it is therefore recommended to use light
sources with a spectrum which is as similar as possible to the spectrum of
normal daylight as e.g. specific metal halide lamps (in Europe e.g.
Hitlite HIT-DE dw (5200 Kelvin) made by BLV, or Power Star HQI ../D or
HQI .../NDL made by Osram, or Biolux lamps made by Osram ).
To measure the total amount of light at a certain place the light meter is
certainly useful. If no light meter is available, the built-in light meter
of many photocameras may give approximate estimations.
Juerg F. Steiger M.D.
Institute for Medical Education IAWF
Master of Medical Education Program
University of Bern, Faculty of Medicine
Inselspital 37a
CH-3010 Bern, Switzerland
Phone: +41 (0)31 632 98 87
Fax: +41 (0)31 632 98 71
juerg.steiger@iae.unibe.ch
http://www.iawf.unibe.ch/MME
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