University home | Faculty of Life Sciences | Research Laboratories home

Lucas Group

Measuring melanopic illuminance

The concept of melanopic illuminance as introduced in al Enezi et al (2011) has been developed in a more recent publication by Lucas et al (2014). In order to appreciate the theoretical basis for this new way of measuring light and the challenges in quantifying irradiance in biologically meaningful units, we recommend reading both of those publications.

Those wishing to calculate melanopic illuminance for humans are directed to the supplementary online material for Lucas et al (2014) which includes an updated melanopic spectral efficiency function as well as an excel-based toolbox excel-based toolbox and associated user guide to help calculate melanopic illuminance. The major difference between the revised melanopic function and that originally proposed by al Enezi et al (2011) is that the function provided by Lucas et al (2014) has been scaled to ensure that melanopic illuminance is equivalent to photopic illuminance for a theoretical equal energy radiator. Melanopic illuminance calculated according to the al Enezi et al (2011) method can be converted into the updated Lucas et al (2014) version by multiplying by 1/5.4.   

In the case of rodents, differences in pre-receptoral filtering mean that the melanopic spectral efficiency function is quite different at short wavelengths (<420nm) from that of humans. In order to ensure consistency with the function for humans proposed in Lucas et al (2014), the method for calculating rodent melanopic sensitivity function proposed by al Enezi et al (2011) has been updated to meet the criterion that melanopic and photopic illuminance are identical for a theoretical equal energy radiator. An excel spreadsheet comprising the revised spectral efficiency function and a method for calculating melanopic illuminance from measured spectral power distributions can be downloaded by clicking here: rodents.  The spreadsheet also provides methods for calculating illuminance relevant for the other rodent photoreceptors (rods and m- and s-cone opsins) following the guidelines outlined in Lucas et al (2014) for calculating a-opic illuminances. 

Although the method outlined in Lucas et al (2014) should now be used to calculate melanopic illuminance, for those who are interested, the legacy melanopic spectral efficiency functions proposed by al Enezi et al (2011) are available upon request ( 


Al Enezi et al (2011) J Biol Rhythms 26(4) 314-323.

Lucas et al (2014) Trends in Neurosciences 37(1):1-9.


<< Back to Research