Step 1: Select Sources

Select from the dropdown menus and use the keyword search bar (optional) below to access the sources that are currently loaded in the calculator. Sources meeting the selected criteria will appear under the Available Sources heading. Press the Reset Filters button to return Step 1 to the default setting.


Below are the list of sources available to be used. Click on a source below to view additional information and have the opportunity to add the source to the calculation area. When the page is first loaded, all preloaded sources will be listed. Use the tools in the Sort Available Sources section to only display sources with the selected metrics. Use the Add Custom Source button to load in additional sources.

Step 2: Edit Variables

Biological input variables are listed below, by name and current setting. All variables default to average values. Click on each variable for additional information and to change the value.

Biological Input Variables Value
Macular Pigment Optical Density: 0.5

Macular Pigment Optical Density: The human retina is not a uniform neural tissue. The highest density of cone photoreceptors in the retina is in the foveal pit, which is used for such visual tasks a reading, threading needles, and identification of distant objects. The macula is a circular region of the retina that extends radially from the fovea with a much higher density of cones than the peripheral retina which is dominated by rods. Most of the visual cortex is devoted to processing images focused in the macula. Therefore, for human conscious perception, the macula is particularly important.

Interlaced among the photoreceptors and the other retinal neurons in the macula is a yellow screening pigment, the macula lutea, that is believed to protect the retina from damage by short wavelengths. The spatial extent of this circular screening pigment is approximately 6-10o with the highest pigment density in the foveal region. Since the macular pigment preferentially filters short wavelengths and since the most effective rays entering the eye are along the optical axis, the spectral sensitivity of the central retina will be influenced by the optical density of the macular pigment.

Importantly, individuals differ quite substantially in the optical density of their macular pigment. The optical density of the macular pigment for different people can range from 0.3 to 0.7; the original model by Rea et al. (2005) assumes a single optical density of 0.5 for all individuals. A new feature of the CS calculator enables users to change macular pigment density for 0.3 to 0.7 in steps of 0.05 to determine how individuals might differ in their effective CS for a given spectral power distribution.

The sources currently selected for measurement are shown below. When an illuminance value (in lux) is entered in the pane to the right of each source, the combined spectral power distribution is automatically updated in the results graph on the far right. If no illuminance value is entered, the source’s illuminance is set at zero.

Enter a vertical illuminance value in lux to determine a CS value based on your chosen SPD.

Source Vertical Photopic Illuminance (lx) Remove Source

No Sources Selected

Step 3: View Results

Below are the output plots displaying information about the combined attributes of light sources that have been selected. Both the graphs and the associated legends will be modified automatically as new sources are added and illuminance values are adjusted.

Spectral Power Distribution


Color Rendering Metrics

The output measurements calculated for the selected sources and their corresponding values are listed below. The output measurements are shown on the left, and the values are shown on the right. Click on the individual outcome measurements for more information.

Measurement Value
CS: 0

Circadian Stimulus (CS) is the calculated effectiveness of the spectrally weighted irradiance at the cornea from threshold (CS = 0.1) to saturation (CS = 0.7), assuming a fixed duration of exposure of 1 hour.

CLA: 0

Circadian Light (CLA) is the irradiance at the cornea weighted to reflect the spectral sensitivity of the human circadian system as measured by acute melatonin suppression after a 1-hour exposure.

Illuminance (lx): 0

Illuminance (lx) is the amount of light (luminous flux) incident on a surface area. Illuminance is measured in footcandles (lumens/square foot) or lux (lx, lumens/square meter). One footcandle equals 10.76 lx, although for convenience 10 lx commonly is used as the equivalent.

Irradiance (W·m-2): 0

Irradiance (W·m-2) is the irradiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The two forms have different dimensions: spectral irradiance of a frequency spectrum is measured in watts per square metre per hertz (W·m−2·Hz−1), while spectral irradiance of a wavelength spectrum is measured in watts per square metre per metre (W·m−3), or more commonly watts per square metre per nanometre (W·m−2·nm−1).

Photon Flux (Photons·m-2·s-1): 0

Photon Flux (Photons·m-2·s-1) is defined as the number of photons per second per unit area


Correlated Color Temperature (CCT, Tcp) is a specification for white light sources used to describe the dominant color tone along the dimension from warm (yellows and reds) to cool (blue). Lamps with a CCT rating below 3200 K are usually considered warm sources, whereas those with a CCT above 4000 K usually considered cool in appearance. Temperatures in between are considered neutral in appearance. Technically, CCT extends the practice of using temperature, in kelvins (K), for specifying the spectrum of light sources other than blackbody radiators. Incandescent lamps and daylight closely approximate the spectra of black body radiators at different temperatures and can be designated by the corresponding temperature of a blackbody radiator. The spectra of fluorescent and LED sources, however, differ substantially from black body radiators yet they can have a color appearance similar to a blackbody radiator of a particular temperature as given by CCT.

Duv: NaN

Duv is a metric defined by American National Standard Institute (ANSI) that quantifies the distance between the chromaticity of a given light source and a blackbody radiator of equal CCT. A negative Duv indicates that the source is “below” the blackbody locus, having a purplish tint, whereas a positive Duv indicates that the source is “above” the blackbody locus, having a greenish tint.


Color Rendering Index (CRI) is a rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural.


Gamut Area Index (GAI) is a measure of color rendering based upon volume in color space. It is the range of colors achievable on a given color reproduction medium (or present in an image on that medium) under a given set of viewing conditions.

Color Coordinates (x,y): NaN, NaN

Chromaticity: The dominant or complementary wavelength and purity aspects of the color taken together, or of the aspects specified by the chromaticity coordinates of the color taken together. It describes the properties of light related to hue and saturation, but not luminance (brightness).

Relative Spectral Power Distribution: (SPD)
Wavelength (nm) Value
Absolute Spectral Power Distribution: (SPD)
Wavelength (nm) Spectral Irradiance (W·m-2·nm-1)