What's the correct term about the colour of lemon juice. Is it bright or light? I am confused between these two terms. When we see any color we can classify it into two main groups: dark or bright /light. Based on Cambridge dictionary the meaning of bright is strong in colour. Does it mean that we can use dark and bright color as synonyms?
There is some overlap and some contrast in the meanings. It matters whether you are talking about paint or light.
If you take a pure yellow colour, such as the yellow colour in the rainbow, or the yellow of the skin of a lemon, this is a bright yellow. Painters use "cadmium yellow paint" for this.
If you take some cadmium yellow paint and mix some white the colour becomes paler, more like the colour of cream. This is a light yellow.
If you take the same yellow paint and add a little black you will get a dark yellow (which quickly becomes brown as you add more black, so "dark yellow" is not actually used very often)
If you have a yellow lamp, there is an ambiguity in the meaning of "bright" as it could refer to the purity of the yellow, or the power of the lamp. A powerful lamp is bright and a weak one is dim. This meaning of "bright" is different from the meaning applied to paint.
Van Gogh used bright yellow paint for his sunflowers paintings.
I used a pale yellow to paint the walls of my bedroom, because the bright yellow was overpowering.
If your urine is a dark yellow, you may be suffering from dehydration. Drink plenty of water!
Light means a color that tends toward white. Dark means a color that tends toward black. Bright means intense in color but not a dark color.
As applied to yellow, in the squares below, the middle center one is bright yellow, the bottom center one is light yellow, and the top left one is dark yellow. Judgment can vary about how to name shades in between.
The difference between lightness and brightness, with respect to color, is a difference in color space used to describe the object. Subjectively some people interchange the usage, and of course conversion from one color space to another is usually possible; that's not always lossless.
HSL (hue, saturation and lightness) is often called the "bi-hexcone model" while HSV (hue, saturation and brightness or value) is often called the "hexcone model".
Wikipedia's webpage HSL and HSB/HSV explains:
The HSB/HSV representation models the way paints of different colors mix together, with the saturation dimension resembling various shades of brightly colored paint, and the value dimension resembling the mixture of those paints with varying amounts of black or white paint.
The HSL model attempts to resemble more perceptual color models such as the Natural Color System (NCS) or Munsell color system, placing fully saturated colors around a circle at a lightness value of 1⁄2, where a lightness value of 0 or 1 is fully black or white, respectively.
Brightness and colorfulness are absolute measures, which usually describe the spectral distribution of light entering the eye, while lightness and chroma are measured relative to some white point, and are thus often used for descriptions of surface colors, remaining roughly constant even as brightness and colorfulness change with different illumination. Saturation can be defined as either the ratio of colorfulness to brightness or that of chroma to lightness.
A simplified and not completely accurate description is to say that lighter objects are whiter while brighter objects are more colorful. In the HSL colorspace an object that is 50% light is equal to an object in the HSB colorspace that is 100% bright. The inaccuracy in such an exact conversion comes from the brain's perception of color.
Referring to lemonade as bright or light yellow is unlikely to spark an argument. Lightness is the perceived reflectance of white. Brightness is how much of the color (not black, grey, or white) is reflected towards your eye (the color intensity, not the white intensity).
Perhaps the easiest way to remember the difference is: Lightness is perceived illumination (assuming white light) while brightness is the luminance, the amount of color (how far from black, with equal amounts of color, furthest away, being white).