Foot candles

Karl Kleiner kkleiner at ycp.edu
Fri Oct 12 10:45:47 EST 2001


Magaly

I don't know of a direct conversion. What you want to do is convert from
a photometric unit (illuminance) to a radiometric (irradiance). The
problem is, most photometric light is in a broader wavelength band than
that considered for plants (PAR 400-700 nm). Correct or not, here is
what I have done.

Convert foot candles to lux -> multiply ft candles * 10.8

Convert lux to Watts m2 ->  lux * 2.45 mW m-1/ 1000 mW W-1

Convert W m-2 to umole m-2 s-1 -> multiply W m-2 * constant.

The constant depends upon the light source, but averages to 4.688 for 11
light sources.

Some specific constants for light in the 400-700 nm range:

Sun & sky, daylight - 4.57
Blue sky only - 4.24
Metal Halide - 4.59
HP Sodium - 4.98
Cool-white fluorescent - 4.59
Incandescent - 5.0

Lux can be converted to umole m-2 s-1, by division: Lux/ constant.
But the constants vary more widely.

Constants for converting light within 400-700 nm.

Sun & sky, daylight - 54
Blue sky only - 52
Metal Halide - 71
HP Sodium - 82
Cool-white fluorescent - 74
Incandescent - 50

This is all from:
Thimijan, Richard W. & Royal D. Heins. (1983) Photometric, Radiometric,
and Quantum Light Units of Measure: A Review of Procedures for
Interconversion. HortScience 18(6): I'm missing page #s


>From Techniques in Bioproductivity and Photosynthesis (J. Coombs et al.
eds.) 1985


Convert Day light, full sun:

	950 W m-2 = 1.36 cal cm-2 min-1 = 95,000 lux
	of this, PAR 9400-700 nm) is: 1800 umole photons m-2 2-1
	this is approx 399 W m-2 = 0.572 cal cm-2 min-1 = 42% of total
	therefore W m-2 (total) = 1.895 umole m-2 s-1 (PAR)

They also have conversions from Blue sky, light and 400W High Pressure
(Sodium Vapor?) lamp

This latter conversion might be easier.

-Karl

"Rincon-Zachary, Magaly" wrote:
> 
> Dear Plant-Eders
> 
> I am in crunch here for time.  I know this question has come up in the list
> some time ago.  What is the conversion factor from foot candle to moles
> photons/sq. meter/sec?
> 
> Thanks
> 
> Not a shred of evidence exists in favor of this idea that life is serious
> 
>                                                            --Brendan Gill.
> 
> Magaly Rincón-Zachary, Ph.D.
> Associate Professor and Graduate Coordinator
> Biology Program
> Midwestern State University
> 3410 Taft Blvd.
> Wichita Falls, TX 76308
> 
> Phone:  (940) 397-4254
> Fax:    (940) 397-4831
> E-mail: magaly.rincon at mwsu.edu
> 
> ---

-- 
______________________________
Karl Kleiner
Assistant Professor of Biology
Department of Biological Sciences
York College of Pennsylvania
York, PA  17405
(717) 815-1754 - Phone
(717) 849-1653 - FAX
kkleiner at ycp.edu
http://goose.ycp.edu/~kkleiner/index.htm

---




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