Selecting, implementing and evaluating control and placebo conditions in light therapy and light-based interventions

Figures & data

Table 1. Criteria for selection of conditions, organized by research question.

Research question	Possible active condition	Adequate control condition	Type of control	Note
Is X affected by light?	Bright light with no specific spectral requirements	Dim light Darkness	Absolute	Measurement of parametric dose–response to intermediate light conditions is advised
Is wavelength A more effective in producing X than wavelength B?	Wavelength A	Wavelength B	Relative	Need to establish some criterion by which wavelength A and wavelength B are matched in exposure (e.g. irradiance/radiance, illuminance/luminance)
Is spectrum A more effective in producing X than spectrum B?	Spectrum A	Spectrum B	Relative	Need to establish some criterion by which spectrum A and spectrum B are matched in exposure (e.g. irradiance/radiance, illuminance/luminance)
Does photoreceptor class A contribute to/drive X?	Modulation spectrum targeted to maximize contrast on photoreceptor class A	Background/reference spectrum	Relative	Limited contrast

Figure 1. Examples of stimulus conditions and the quantification of their effects in an α-opic framework. Metameric spectra are from [88]. Code to produce the figure and underlying data can be obtained from https://github.com/tscnlab/Spitschan_AnnMed_2023.

Schöllhorn I, Stefani O, Lucas RJ, et al. Melanopic irradiance defines the impact of evening display light on sleep latency, melatonin and alertness. Commun Biol. 2023;6(1):228.

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Data availability statement

Code to produce the figure and underlying data can be obtained from https://github.com/tscnlab/Spitschan_AnnMed_2023.