APOGEE

Frequently Asked Questions
Topics
 CONVERSION: PPF to Foot-candles
  
PPF (µmol m-2 s-1)
TO FOOT-CANDLES
Sunlight
5.01
Cool White
Fluorescent
Lamps
6.87
High Pressure
Sodium Lamps
7.62
High Pressure
Metal Halide Lamps
6.60
Low Pressure
Sodium Lamps
9.85
FOOT-CANDLES
TO PPF (µmol m-2 s-1)
Sunlight
0.200
Cool White
Fluorescent
Lamps
0.146
High Pressure
Sodium Lamps
0.131
High Pressure
Metal Halide Lamps
0.152
Low Pressure
Sodium Lamps
0.102

Multiply the PPF by the conversion factor to get foot-candles. For example, full sunlight is 2000 µmol m-2 s-1 or 10,020 foot-candles (2000 * 5.01).

Multiply the foot-candles by the conversion factor to get PPF. For example, full sunlight is 10,020 foot-candles or 2000 µmol m-2 s-1 (10,020 * 0.2).
   
 PPF TO FOOT-CANDLE REFERENCE TABLE
 
SUNLIGHT
If PPF is:
then, fc is:
10
50.1
100
501
200
1,002
300
1,503
600
3,006
1,000
5,010
*2,000
*10,020
 
COOL WHITE FLUORESCENT
If PPF is:
then, fc is:
10
68.7
100
687
200
1,374
300 
2,061
600
4,122
1,000
6,870
2,000
13,740

* Full sunlight at solar noon on a clear summer day.
 DEFINITIONS
PHOTOMETRIC UNITS, ILLUMINANCE:
FOOT-CANDLE = one lumen per square foot.  The 16th General Conference on Weights an Measures (CGPM), Oct. 1979, decided that the candela is the luminous intensity of a source emitting monochromatic radiation of frequency 540 x 1012 Hz and radiant intensity 1/683 watt per steradian.  This corresponds to 683 lumens per watt of radiation at approximately 555 nm wavelength, which is near the maximum of the standard photopic spectral luminous efficiency curve.

LUX = one lumen per square meter; differs from foot-candle by about a factor of 10.
QUANTUM UNITS, PHOTON FLUX DENSITY:
MICROEINSTEIN per second and square meter  (µE m-2 s-1).  The einstein has been used to represent the quantity of radiant energy in Avogadro's number of photons and also Avogadro's number of photons.  The second definition has the einstein equal a mole of photons. While commonly used as a unit for photosynthetically active radiation (PAR), the einstein is not an SI unit.

MICROMOLE per second and square meter (µmol m-2 s-1).  This term is based on the number of photons in a certain waveband incident per unit time (s) on a unit area (m2) divided by the Avogadro constant (6.022 x 1023 mol-1).  It is used commonly to describe PAR in the 400-700 nm waveband.
DEFINITIONS FROM:
Thimijan, Richard W., and Royal D. Heins. 1982. Photometric, Radiometric, and Quantum Light Units of Measure:  A Review of Procedures for Interconversion. HortScience 18:818-822.