Red also became the color of revolution; Soviet Russia adopted a red flag following the Bolshevik Revolution in 1917, later followed by China, Vietnam, and other communist countries.
Since red is the color of blood, it has historically been associated with sacrifice, danger and courage.
The remaining reddened sunlight can also be scattered by cloud droplets and other relatively large particles, which give the sky above the horizon its red glow.
and these two types of lasers were widely used in many scientific applications including holography, and in education.
It is a primary color in the RGB color model and the CMYK color model, and is the complementary color of cyan.
Reds range from the brilliant yellow-tinged scarlet and vermillion to bluish-red crimson, and vary in shade from the pale red pink to the dark red burgundy.
Red, green and blue light combined together makes white light, and these three colors, combined in different mixtures, can produce nearly any other color.
In the language of optics, red is the color evoked by light that stimulates neither the S or the M (short and medium wavelength) cone cells of the retina, combined with a fading stimulation of the L (long-wavelength) cone cells.