Visible light. Part I: Properties and cutaneous effects of visible light

Abstract

Approximately 50% of the sunlight reaching the Earth's surface is visible light (400-700 nm). Other sources of visible light include lasers, light-emitting diodes, and flash lamps. Photons from visible light are absorbed by photoreceptive chromophores (e.g., melanin, heme, and opsins), altering skin function by activating and imparting energy to chromophores. Additionally, visible light can penetrate the full thickness of the skin and induce pigmentation and erythema. Clinically, lasers and light devices are used to treat skin conditions by utilizing specific wavelengths and treatment parameters. Red and blue light from light-emitting diodes and intense pulsed light have been studied as antimicrobial and anti-inflammatory treatments for acne. Pulsed dye lasers are used to treat vascular lesions in adults and infants. Further research is necessary to determine the functional significance of visible light on skin health without confounding the influence of ultraviolet and infrared wavelengths.

Keywords: chromophores; lasers; optical radiation; photobiomodulation; photodermatitis; phototherapy; porphyria; visible light.

Figure 1:. Electromagnetic radiation spectrum.

UVR, VL, and IR are optical radiation. VL can be divided by color: blue/violet (400–500 nm), green (500–565 nm), yellow (565–590 nm), orange (590–625 nm), or red (625–700 nm). Similarly, UVR is separated into separate spectra: UVA (320–400 nm), UVB (290–320 nm), UVC (200–290 nm), and extreme (EUV; 10–120 nm). IR can be subdivided into IRA (near-IR; 700–1440 nm), IRB (mid-IR; 1440–3000 nm), and IRC (far-IR; 3000 nm-1 mm) wavelengths. Spectral boundaries are not discrete, and there is an overlap in the biological effects between adjacent forms of EMR.

Figure 2:. Diagram of natural and artificial visible light sources.

Devices are labeled with significant parts. Collimation (i.e., parallel), coherence (i.e., in-phase), and chromaticity are provided for each light source. (A) Sunlight is relatively collimated at the surface of the Earth. (B) Lasers pump energy through a gain medium (e.g., crystal or gas) to generate or amplify light between mirrors in the resonator cavity. The variable attenuator in the resonator cavity of Q-switched lasers allows for beam pulsing. Lasers are highly monochromatic, coherent, and collimated upon emission. (C) Light-emitting diodes (LEDs) pass an electrical current through a semiconductor. LEDs produce light in a narrow range to appear as a single color. Multiples LEDs can be placed in an array to generate white light or higher power densities. (D) Arc and flash lamps (e.g., intense pulsed light [IPL]) arc electricity through a mercury or xenon gas chamber and are optimized for continuous and pulsed operating conditions, respectively. Filters are applied to achieve specific wavelengths. (E) Halogen lamps heat a tungsten filament in a sealed chamber with small amounts of halogen gas. (F) Fluorescent lights excite electricity through mercury gas to produce UVR, which is converted to VL via the phosphorescent coating on the lamp’s inner surface.