**5. Conclusions**

The length of internodes and petioles increased under low BPFD, similar to the shade response under low PPFD, whereas the limited response of SLA and internode diameter indicated that the shade responses of these might not be regulated by cryptochrome. Further studies could investigate alternative regulation of these together with extended photosynthetic measurements over time to increase the understanding of carbon assimilation and translocation under different BPFD levels. Several aspects of the exact spectral effects on morphology and physiology should be further investigated, both for narrow peaks independent and the interactions with broader spectra.

Internode length dependent on perceived BPFD was well simulated in the FSP model and the simulations gave an increased insight into the response of the second and third internode based on the perceived BPFD. The model was a useful tool to determine the minimum necessary BPFD within an alternative chamber environment. Modelling with an FSP can be applied for further optimizations of indoor plant production implementing advances in knowledge of spectral effects on plant morphology and physiology.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2223-7747/9/12/1757/s1, Figure S1: Plant height (A), biomass (B) and leaf area (C) per plant and under different blue photosynthetic flux densities (BPFD). Error bars indicate standard error of the mean (day 9–20: *n* = 4, day 23: *n* = 8), Figure S2: Simulated (line) and measured (points) length of petioles, internodes and leaf laminas under the treatments B310 and B60, Figure S3: The absorption, reflection and transmission of radiation (%, relative to the incident radiation) from 400–700 nm by a soybean leaf used for the optical properties of the simulated soybean leaves. Data taken from Kasperbauer (1987), Figure S4: The simulated spectra (total PFFD of 400 µmol m−<sup>2</sup> s −1 ) of the six treatments with a simulated BPFD of 60, 110, 160, 210, 260 and 310 µmol m−<sup>2</sup> s −1 , Figure S5: Visualizations of the simulated unfolding (A, B) and fully developed (C) trifoliate leaf, Table S1: The spread of the six treatments within three chambers over time, Table S2: Model inputs to determine ratios and angles of organs.

**Author Contributions:** Conceptualization, T.H. and S.M.; methodology, T.H. and S.M.; software, T.H.; validation, T.H.; formal analysis, T.H.; investigation, T.H.; data curation, T.H.; writing—original draft preparation, T.H.; writing—review and editing, T.H., S.M. and S.G.-H.; visualization, T.H.; supervision, S.M. and S.G.-H.; project administration, T.H., S.M. and S.G.-H.; funding acquisition, S.M. and S.G.-H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the German Federal Ministry for Economic Affairs and Energy according to a decision of the German Federal Parliament within the Central Innovation Program for SMEs (ZF4279901CR6).

**Conflicts of Interest:** The authors declare no conflict of interest and the funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
