The amount of light that actually reaches the retina depends not only on the luminaire but also on the optical properties of the eye itself. The human lens gradually yellows with age due to the accumulation of chromophores—products of protein oxidation and glycation in the lens. This process increases absorption of short wavelengths and reduces lens transmission, especially in the blue and cyan regions of the spectrum. Transmission for red light remains relatively stable with age.
The extent of this attenuation depends on the specific wavelength, age, and individual condition of the lens. In a healthy lens without cataracts, the decrease in transmission in the cyan region (around 480 nm) is gradual—more significant changes are typical for advanced nuclear cataracts rather than normal aging. Exact values in the literature vary depending on measurement methodology, and this variability should be considered.
From a practical perspective, this means that older adults require higher lighting intensity than younger individuals to achieve the same level of retinal stimulation—especially in wavelengths relevant for circadian regulation. This fact has been well-known and discussed in gerontological photobiology and lighting design for seniors at least since the early 2000s.
Luminaires with conventional LED spectra have lower output in the cyan region (see the cyan gap described above). In older users, this spectral deficit combines with the natural lens attenuation—so the resulting stimulation of melanopsin cells may be lower than the nominal intensity of the luminaire would suggest. This is a valid argument for Spectrasol pro-cognitive lighting with stronger representation of the cyan region, especially in environments such as senior homes or hospitals, where sleep quality and circadian rhythm are clinically relevant.
It is important to add, however, that sleep disorders and circadian desynchronization in older adults have multiple causes—changes in the intrinsic period of biological clocks, decreased amplitude of melatonin secretion, comorbidities, and medications affecting sleep. Lighting is one factor, not the only one, and its optimization should be part of a broader approach, not an isolated solution.
