Converting lux to RGB color space to run in PsychoPy

I am coding stimuli in PsychoPy that was previously done in Inquisit. The authors note the luminance values in lux units. As far as I can see, my best option is to determine this in DKG or RGB color space. However, I cannot seem to find the best method to get from a single value in lux to the three value coordinates of RGB or DKG.

Example: the authors report a lux of 5.2. How can this be converted to work within PsychoPy?

Does anyone have experience with this?

It can’t be done: any illuminance value in lux could be achieved by any combination of colours. It’s the equivalent of trying to work out the frequency content of a sound after only being given a measure of that sound’s volume. A loud sound can be of any pitch, just as a bright light can be of any colour.

Illuminance is weighted by wavelength, but it is still just a unitary summed value across the range of wavelengths.

Lastly, let’s say you find out the desired colour values. The achieved illuminance value can’t be determined in software: it must be measured empirically, using appropriate hardware. It depends on the characteristics of the display device.

Hi Michael,
Many thanks for your answer. I did not think of it this way. But this of course makes sense.

So, since the color is not really what matters for changing the luminance, how would one go about this to adjust the luminance of a stimuli over 5 intervals?

For example, if I wanted to the luminance of the stimuli to double at each interval. Would this be possible in PsychoPy, regardless of the color chosen?