The human eye is not equally sensitive to all wavelengths of visible light. The visible spectrum extends from a wavelength of approximately 400nm to 700nm.
Luminosity Function -Legend:
X-Axis Wavelength; y-Axis: Relative Sensitivity
Green Curve: scotopic vision (nighttime)
Black Curve: photopic vision (daytime)
LEDs create a narrowband stream close to the visible, the ultraviolet and the infrared light frequencies.
The color of the emitted light by an LED is defined by the semiconductor material. Possessing a varying ability to conduct electrical current, the semiconductor material influences the dominant wavelength of the emitted light.
The dominant wavelength describes the distance between successive points of equal amplitude and a phase on the wave.
LEDs using AlInGaP compound semiconductor alloys emit light in bands ranging from green to red, while the light emitted by LEDs using AlInGaN compound semiconductor alloys color ranges in the UV-blue-green spectrum. White light can be generated by blending the light of a blue LED with a yellow phosphor. The phosphor converts a part of the blue light into yellow light and, depending on the ratio, different color temperatures can be created.
AIGaAs - Aluminum Gallium Arsenide
Red, Orange, Yellow
AllnGaP - Aluminum Indium Gallium Phosphide
Red, Orange, Yellow
GaAsP - Gallum Arsenide Phosphide
InGaN - Indium Gallium Nitride
Table 1 - Light Emitting Diode - Color variation
Multicolored LED (RGB)
Basically LEDs are monochromatic devices; they generate a single color light depending on the used semiconductor material. By applying different voltages, the color can change slightly, but the actual color spectrum is still strongly limited.
In order to have access to a larger color spectrum, a multicolored LED was developed consisting of three diodes in a single package (SMD) in red, green and blue (RGB). Compared to single-colored LEDs, RGB LEDs generate an almost unlimited color spectrum of up to 16.7 million. Due to their enormous color range, tiny size and environmental friendliness the field of possibilities of LED-lighting ranges from basic illumination to architectural design and renders application such as large video screens or color changing luminaires for lighting of whole buildings possible.
White light produced by environmentally friendly and energy saving LEDs gains more and more attention and aims at replacing conventional light sources already in the near future.
Firstly, white light was only possible by using a group of three LEDs; red, green and blue. By integrating them into one common LED housing and yielding their color to each other, an overall white light output could be created.
Nowadays the industry provides a more homogeneous white light using chip level conversion (CLC), applying a thin phosphor layer on top of the semiconductor. Stimulated by a blue LED, the phosphor begins to emit a yellowish light. Depending on the intensity of the blue LED and type of phosphor, different color temperatures can be created. Traxon Technologies divides white LEDs into three color temperature groups: cold white, warm white and dynamic white.
The CIE Chromaticity system stands for ‘Comission Internationale de l’Eclairage’ and is based on the idea that any color can be generated by the addition of appropriate intensities of light from the three primary colors (red, green and blue).
Correlated Color Temperature (CCT)
In general, colors can be felt as warm or as cold. Because the terms 'warm' and 'cool' are associated with temperature, a more technical description of a lamp's color appearance is color temperature, measured in Kelvin (K). The warmer a light is perceived, the lower is the color temperature; the colder a light appears, the higher is its color temperature.
In order to define the exact shade of white, White Light is measured in color temperature along the Black Body Curve rather than using the CIE Chromaticity Diagram commonly used to describe the wavelengths at which colored light is emitted. The position along the Black Body Curve is equivalent to the color of a black iron body being heated to thousands of degree Kelvin. These ‘color temperatures’ have been defined and can be laid over the Chromaticity Diagram resulting in a Correlated Color Temperature (CCT), referring to the closest point in the diagram to the Black Body Temperature.
Color Rendering Index (CRI)
The extent to which light is capable of making objects appear their true color is known as color rendering. The Color Rendering Index (CRI) is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source measured in Ra. The scale ranges from 0 to 100, with 100 being as good as natural daylight.
Light sources with a high CRI are desirable in color-critical applications such as photography, cinematography – or other areas such as retail environments.
Color Rendering Index (Ra)
Compact Fluorescent Lamp (CFL)
Mercury Vapor High Pressure Discharge Lamp
Tungsten Halogen Lamp
Low Pressure Sodium Lamp
Metal Halide Lamp
Light Emitting Diode
Typical Color Rendering Index (Ra) requirements for certain application areas are, e.g.:
The Illuminance describes the amount of light emitted onto a surface. The measurement unit for illuminance is lumen per square meter (lm/m2), also called lux (lx). The lux level diminishes with the distance to the illuminated surface. The higher the illuminance, the higher is the ability of the eye to distinguish details, small contrasts and color hues. Therefore, different activities require different levels of illuminance.
How much light do you need?
Type of Activity
Illuminance (lx = lm/sqm)
Orientation and simple visual tasks (public spaces)
Common visual tasks (commercial, industrial and residential applications)
Special visual tasks, including those with very small or very low contrast critical elements
Color defines…RGB LED lighting can dynamically phase through any number of colors. This option makes the LED light very attractive for the architainment sector
Color calls attentions…Colors visually enhances and attracts, especially when the colors are placed in unconventional spots. This effect gets all the more intense when a color change is noticed as a movement. In display windows and showrooms, as well as in the advertising industry color is an indispensable eye catcher. With LED light the world is getting more colorful.
Color relaxes…Colored light installations can improve the recreational process; they can be used as part of color therapies, as elements of interior design or to change the ambience of a space, as well as to decrease stress in places such as waiting and treatment rooms.
Color upgrades…Color shapes, calls attention and lightens up – and thus color appreciates the overall ambiance. The aims are imperative to restaurants and bars, which use color changing LED light on walls, ceilings or in appliances such as bar counters.
Color is playful…Color changing LED light also works brilliantly in the entertainment industry – where color can be used in a wider variety of ways. With the aid of incentive programming, fascinating lighting scenarios can be achieved.
Step by step safeness…The risk of stumbling decreases when obstacles are well indicated. Using LED accents such as step lighting, this is easily achieved.
Light plays an important role for the human being. The main percentage of our impressions is based on the human sight, together with a functioning human eye, light therewith builds the basis for the human sight.
Next to its basic function to illuminate the environment, light takes direct effect on people. It does not only influence directly our biological clock (“Circadian rhythm”), rendering us active during the day and helps us recovering during the night, but also provokes physiological responses as well as influences the visual and mental perception of human beings.
On the one side light can contribute and increase the general well-being, task performance, aesthetical impression of the environment or the emotional ambiance. On the other side, however, light can also take negative influence on the human health.
Light plays therefore an important role for the human being, influencing him not just in a visual way, but also in an emotional and biological way.
Light and health
The human body is a complex physiological being, which corresponds to its environment. The light is an important factor which takes considerable influence on the well-being. It has significant biological as well as psychological effects.
Besides its function for human sight and control of the Circadian Rhythm, it also influences directly the human, e.g. productivity, concentration or even mood and health. Negative effects of suboptimal lighting are, amongst others, increase of headache, worker fatigue as well as medically defined stress or increase in anxiety. Furthermore, it can even result in higher blood pressure which can lead to even further diseases.
Light and performance
As light takes direct effect on the human system and body, it can also function as stimulus to the human-being, resulting in an increase of alertness, attention and concentration. Besides the biological effect of light, it also enhances the visual function, resulting in increasing performance and can even create emotional effects such as feelings of comfort and motivation.
Several studies prove the relationship between productivity and lighting. According to the National Lighting Bureau “Light affects performance in two ways: directly and indirectly. The direct effects occur because lighting alters how well we can see, either by changing the stimuli to the visual system or by changing the operating state of the visual system. The indirect effects occur because lighting can gather attention; alter arousal, mood and behavior; and modify the body’s hormone balance.”
Light and perception
Light builds the basis for between 80 to 85 percent of our impressions and can influence the human-being not just in a biological way, but also in an emotional way. How a space is illuminated can form the perception of humans and of how they perceive their surroundings. The perception of the environment is a fundamental factor of the basic mood of a human-being. A space where the human-being does not feel comfortable and unwell does decrease his productivity, motivation and can furthermore take effects on his health as well.