What is the light spectrum of different visible light sources ? The visible spectrum is the portion of the electromagnetic spectrum, Visible light comprises only a tiny fraction of the entire electromagnetic radiation spectrum, yet it contains the only region of frequencies to which the rods and cones of the human eye will respond. The wavelengths that humans are typically able to visualize lie in a very narrow range between approximately 400 and 700 nanometers.In terms of frequency, this corresponds to a band in the vicinity of 400–790 THz. Humans can observe and respond to stimuli created by visible light because the eyes contain specialized nerve endings that are sensitive to this range of frequencies. However, the remainder of the electromagnetic spectrum is invisible. These boundaries are not sharply defined and may vary per individual.Under optimal conditions these limits of human perception can extend to 310 nm (UV) and 1100 nm.

1. What is the light spectrum of different visible light sources ?
The visible spectrum is the portion of the electromagnetic spectrum, Visible light comprises only a tiny fraction of the entire electromagnetic
radiation spectrum, yet it contains the only region of frequencies to which the rods and cones of the human eye will respond. The wavelengths
that humans are typically able to visualize lie in a very narrow range between approximately 400 and 700 nanometers.In terms of frequency, this
corresponds to a band in the vicinity of 400–790 THz. Humans can observe and respond to stimuli created by visible light because the eyes
contain specialized nerve endings that are sensitive to this range of frequencies. However, the remainder of the electromagnetic spectrum is
invisible. These boundaries are not sharply defined and may vary per individual.Under optimal conditions these limits of human perception can
extend to 310 nm (UV) and 1100 nm.

2. Visible light wavelength and perceived colors

3. Visible light sources from nature:
During day time, sunlight is enough for outside on earth, there are also some differences in sunlight spectrum at different latitudes and at different
times of day.

4. At night, natural light is produced by celestial bodies, such as the moon, planets, and stars, in addition to the periodic Aurora Borealis (Northern
Lights), and the occasional comet or meteor ("shooting star"). Other natural light sources include meteorological lightning, volcanoes, forest fires,
plus some biochemical sources of visible light (bioluminescence). The biological light sources include the familiar lightning bugs ("fireflies") and
more exotic glows from the sea, including bioluminescent species of bacteria, algae, dinoflagellates, jellyfish, comb-jellies (ctenophores), and
some species of fish.
Moonlight spectrum

5. Light spectrum of artificial visible ligght sources:

6. XED light source
XED(Xenon Energy Discharge Lamp), working principle: Xenon gas with high voltage excitation, the free electrons in the lamp electric field obtain
enough energy to collision atom, so that it releases more free electrons, which cause the gas lamp continuous avalanche discharge, thereby
releasing out of electromagnetic waves, and ultimately achievethe purposeofgasdischarge light.

7. Led light source
A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor
recombine with electron holes, releasing energy in the form of photons. The color of the light (corresponding to the energy of the photons) is
determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple
semiconductors or a layer of light-emitting phosphor on the semiconductor device.

8. Fluorescent light source
A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An
electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of
the lamp to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. The typical
luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable
light output.

9. HPS light source
A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.
Two varieties of such lamps exist: low pressure and high pressure. Low-pressure sodium lamps are highly efficient electrical light sources, but
their yellow light restricts applications to outdoor lighting, such as street lamps, where they are widely used.[1] High-pressure sodium lamps emit a
broader spectrum of light than the low-pressure lamps, but they still have poorer color rendering than other types of lamps.[2] Low-pressure
sodium lamps only give monochromatic yellow light and so inhibit color vision at night.

10. Mercury light source
A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is
generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. The outer bulb may be clear or coated with
a phosphor; in either case, the outer bulb provides thermal insulation, protection from the ultraviolet radiation the light produces, and a convenient
mounting for the fused quartz arc tube

11. Incandescent light source
An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The
filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxidation. Current is supplied to the filament by
terminals or wires embedded in the glass. A bulb socket provides mechanical support and electrical connections.
From above we know that, the visible light both comes from nature and artificial lighting sources, their visible spectrums are different, the human
brain adjusts automatically to the different light sources, and we interpret the colors of most objects around us as hardly changing when they are
viewed under differing conditions of illumination.