It's the scientific concensus (unless you reject all of the evidence that's out there for the past 15 years). We have multiple receptors in our eyes to do sign

It's the scientific concensus (unless you reject all of the evidence that's out there for the past 15 years). We have multiple receptors in our eyes to do signalling, it's likely that only the S cone cell (low wavelength receptor) suppresses melatonin. This study found no melatonin suppression for higher wavelength light: http://www.ncbi.nlm.nih.gov/pubmed/14962066 http://www.ncbi.nlm.nih.gov/pubmed/14962066 This study also showed the wavelength effect (may be the first big publication on the topic?): http://www.ncbi.nlm.nih.gov/pubmed/11763987 http://www.ncbi.nlm.nih.gov/pubmed/11763987 In addition, not only is it an observed effect, but it can be harnessed. This study showed increase in salivary melatonin by using glasses that filtered lower wavelengths of light: http://www.ncbi.nlm.nih.gov/pubmed/15713707 http://www.ncbi.nlm.nih.gov/pubmed/15713707 The effect is such a strong one that it was discovered despite not being one of the measurements in an unrelated experiment on breast cancer. And throughout antiquity, the only light at night we're exposed to has been that of fire, which is a higher wavelength source.