The wise pick up on the details here Sunlight conditions the immune system, tanning beds just tan skin UV-A and blue light in the morning from the sun boost T-cell motility and immune surveillance through nitric oxide release and specific photoreceptor pathways in the skin This effect is spectrally coordinated along with circadian timing UV-A rises after dawn, alongside visible light and IR, priming immune cells to patrol tissues more effectively Tanning beds, on the other hand, blast narrow UV spectra in isolation, nearly always without the proper timing, visible light balance, or infrared context that drives this immune activation So while they may pigment the skin or raise Vitamin D with repeated use, they don’t replicate the immune tuning role of sunlight.. no sunrise gradient, no nitric oxide surge, no circadian signaling The devil is in the details here