Photobiology (non-ionizing radiation)

Note: the study of ionizing radiation on living systems is radiobiology.

UV on plants.

Plants are good absorbers of UV, but plants have their own sunscreen, called sinapate esters (such as sinapoyl malate) as well as flavonoids, to shield UV-B. Plants have evolved ways to shield UV-B when exposed to UV. UV-C has been shown to increase branching on greenhouse ornamental plants.

IR on plants.

For plants, IR can cause certain flowers to bloom. Plants require mostly blue and red light for photosynthesis, but for flowering, IR is needed. Red and IR further is needed for plant growth. Blue light is more controlling for the opening and closing of stomata than other colors, while plants grow more under red light than blue. Blue light can stunt plant growth, even at 6% blue light and 94% red light. However, very few plants have been tested for growth between red light vs. blue light.

UV on bacteria.

Ultraviolet radiation causes detrimental effects on the cell by mutating its DNA. However, Micrococcus luteus and Micrococcus radiophilus are 2 bacterial species known to be able to withstand high levels of UV radiation. Of a study of 75 bacteria screened for UV tolerance, Gram positive Bacillus strains were the most resistant.

IR on bacteria.

Far-IR is also known to kill bacteria, specifically Staphylococcus epidermidis.

From a 2020 study, near-IR of 780 nm and 808 nm have been able to kill over 99% of S. aureus and E. coli within 15 minutes, via a composite coating. The composite coating that was constructed on Ti plates, and MnO₂ and polydopamine for a surface system. The polydopamine improved the light-absorption of the system. This was put as a promising system to kill bacteria on biomedical devices.

However, blue light, specifically at 415 nm, is better at killing bacteria than red light.

Case study: the effect of light on humans.

Did you know that the most dangerous night light to use during sleep is spectral-blue? Followed by green, then violet, and the safest being red, then orange. That's because sleeping with blue-spectral light can cause cancer. Though the spectral light does not directly cause cancer, it disrupts and reduce melatonin production, which can cause cancer. That is because melanopsin, the light-sensitive protein in special retinal cells (ipRGCs) peaks at around 480 nm. Red light does not activate it.

Now, we are strictly talking LED light. Because an incandescent light bulb that is painted blue, is not actual blue nm wavelength. An incandescent light bulb can be painted any color, and still won't be spectral-blue wavelength. Incandescent light bulbs, like the sun, being heat-driven, emit mostly IR light, with the rest being in the red and orange visible range, with only trace amounts in green and blue. This is why incandescent light bulbs are generally painted white.