The High-brightness (HB) LED which have
more advantages than traditional lighting solutions is become increasingly
popular. One of the advantages of high brightness LED is its ability to produce
different colors. The essence of the color mixture is to mixing the base
primary color in appropriate proportions to generate the secondary color. This
article will explain the science behind color mixing, including those involving
mathematical formulas and how to apply them effectively.
Color mixture
and multi-point excitation space principle
The
basic properties of light are not primary colors, but often involve
psychological reaction when the eyes receive light. Color model can be
expressed in different ways. Modeling goal is to minimize the complexity of the
formulas and the number of variables, while maximizing the essence and
coverage. Traditionally, no matter what the meaning assigned to the variable,
which is sufficient to describe all three colors: RGB, Hue - Saturation -
Brightness (HSB). Other based on shades - saturation model, as Lab and XYZ.
Their common feature is a variable quantity or dimension.
In
the multi-point excitation space, color excitation is
mark by letter R, Q, G, B, and A. Q refers to excitation of any color, the
letter R, G, B and A, are expressed the selected basic fixed excitation for
color blending. Red, green, blue and amber are fundamental excitation. Color
matching means for a given excitation Q determined by a variety of basic
excitation R, G, B and A with appropriate quantities obtained additional
mixture color which is available expressed as vector equation.
Q=RqR+GqG+BqB+……+AqA
(equation (1))
In
the multi-dimensional space, color excitation Q is expressed by
multiple-support excitation vector Q. Scalar
multiplier RQ, GQ, BQ and AQ are excited by a given basic excitation R, G, B
and A which are in units of measure by convention. Unit
vectors R, G, B, and A represents a fundamental excitation, which define the
space. They have a common starting point to four different directions.
Figure
1: multi-dimensional color space
The
origin of vector Q is the same as R, G, B and A. It located by the R, G, B and
A defined axes, lengths equal to Q multi-stimulus values RQ, GQ, BQ and AQ.
We can obtain the direction and length by a defined
formula equation (1). The space which defined by R, G, B and A is called a
multi-excitation.
Color
Mixture
Figure
2 shows the CIE 1932 chromaticity diagram. There are three colors in the figure
2: Red, Green, Blue. Through three
colors mixed in appropriate proportions, we can get all the colors on the
connection. This area is called the color
gamut. However, in the CIE 1931 standard, the
color distribution is uneven and discontinuous. For calculated ratio of primary
color in determining to form the desired secondary color, the linear transformation can’t be used.
Blending
algorithm
In mixing colors
applications, the firmware in accordance with CIE chromaticity coordinates input values. For each LED channel,
it converted coordinate into values of the appropriate dimming. In laymen's terms, dimming value is the LED dimming range that must have the corresponding
maximum flux. If intelligently and
quickly turned off the LED bulb current, can be implemented to control the LED
luminous flux output. The firmware will let the coordinate combines with LED
knowledge in the pre-programmed system. Then, it will be necessary to finish the chromaticity coordinates
correctly converted into a luminance value of each LED.
