Re: How to convert microeinstiens to lux

Light measurements can be complicated but illuminating...

Photometric units, illuminance:
    Footcandle = 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.

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. 
          Therefore: microEinsteins per m2 per second is identical to
          micromoles per m2 per second. 
          (1000 µE m-2 s-1 = 1000 µmol m-2 s-1)
    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 10e23 mol-1).  It is used commonly to 
          describe PAR in the 400-700 nm waveband.

The approximate conversion factors given below will help to 
convert absolute energy units or irradiance units (PAR) 
as recommended by the plant scientist into illuminance 
or photometric values (lux).

                         Radiometric      PAR        - Photometric
        Source*             W m-2        µE m-2 s-1     fc      lux

        HP Sodium            1               5         33.5     360
        (400 w)              1              6.7        72.3
                             1             10.8

        Metal Halide         1              4.6        29.6     319
        (400 w)              1              6.5        69.5
                             1             10.8

        Mercury              1              4.7        30.8     332
        (400 w)              1              6.5        70.0
                             1             10.8

        CW Fluorescent       1              4.6        34.2     367
          (215 W)            1              7.44       80.0
                             1             10.8

To convert from either W m-2 or µE m-2 s-1 to photometric units, multiply
by the appropriate factor.