Can someone help me compare apples and oranges?
I made some light intensity measurements in my lab using a quantum sensor
for PAR (400-700 nm), so the units are umoles photons per m2 per sec. My
purpose was to help our operations folks design better room lighting. I
realize that architects are used to measuring light in units such as lumens
or foot-candles. My problem is to try to convert. I know it can't be done
exactly, because one is measuring different things. But assuming the
spectral distribution of a typical fluorescent light bulb, does anyone have
a rough approximation of a conversion?
Carl S. Pike (717) 291-3958
Department of Biology FAX (717) 399-4548
Franklin and Marshall College Internet C_PIKE at ACAD.FANDM.EDU
P.O. Box 3003
Lancaster, PA 17604-3003 USA
PAR measurement under cool white fluorescent of 27 micro moles is equal to
c. 200 lux ie 200 lumens per m2 or c. 2000 foot cadles (lumens per ft2).
This ratio only holds for the particular light source but will be generally
OK for most fluorescents
APOLGIES FROM
AS POINTED OUT BY JONATHON MARDER I GOT MYSELF MIXES UP BETWEEN LUX AND
FOOT CANDLES, IN THE CASE QOUTED ABOVE IT SHOULD BE 27 MICRO MOLES PHOTONS
= 2OOO LUX WHICH IS V APPROXIMATELY = TO 200 FOOT CANDLES. I DID THIS
CRUDELY IN THE LAB WITH 2 METERS SIDE BY SIDE.
AS A ROUGH RULE OF THUMB FULL SUNLIGHT IS APPROXIMATELY 2000MICRO MOLES
QUANTA, IS 100 000 LUX, IS 10 OOO FT CANDLES I BELIEVE.
I HAVE NOW LOOKED UP THAT V EXCELLENT PUBLICATION HALL ET.AL.
PHOTOSYNTHESIS AND PRODUCTIVITY IN A CHANGING ENVIRONMENT CHAPMAN AND
HALL. AND THEY GIVE A TABLE OF CONVERSIONS BASED ON THE WORK OF MCCREE
WHICH SAYS THE FLOURESCENT CONVERSION IS 1000LUX=12MICRO MOLES WHICH IS
CLOSE TO THE ONE I FOUND WITH MY METERS. IT DOES DEPEND V MUCH ON THE TYPE
OF LAMP AS THE PHOTOMETRIC MEASURE IS BASED ON THE HUMAN EYE SENSITIVITY.
Warwick Silvester Ph. +64-7-838 4613 and voicemail
Dept of Biological Sciences Fax +64-7-838 4324
University of Waikato Email w.silvester at waikato.ac.nz
Hamilton, New Zealand
