That may depend on the plant species you are working with.  I found that with Chenopodium album lowered red to far-red light ratio delayed flowering contrary to other work with other species.

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Thank you for your answer

You may take a general info from George Bernier http://www.ncbi.nlm.nih.gov/pmc/articles/PMC160348/pdf/051147.pdf. As far light dependent quantitative flowering  you should take different units (and instruments) as lux is calibrated on human photopic response and has little far red and red in it. A radiometer with extended spectral response (320-1100 nm, like Hamamtsu  S 1087-01) is the correct choice. Photoperiodic plants are sensitive to day legth for induction,but expression rates may depend on fluence rate. Red -far red ratios in the open field havre a limited effect.You may see specific infos according to your application, but several olants require a thermoperiod for induction.

I suggest to use a ratio equal to 1 for red: red far ratio, meaning red = red far for your purposes.

Regards

In soybean, red : far red ratio causes the different photoperiod reaction depending on genotype. E loci which are responsibe for daylength reaction interact with R:FR ratio.

See: Cober E.R., Tanner J.W., Voldeng H.D. Soybean photoperiod-sensitivity loci respond differentially to light quality // Crop Sci. 1996, 36: 606-610.

Thank you so much for your responding. I got lots of information with your help.