gindex

The gindex function calculates the spectral G-index, a scalar unit corresponding to the energy contribution of the blue part of a given spectral power distribution (SPD). Higher G-index values correspond to lower spectral power distribution in the blue region of the spectrum.

Formula:

G = -2.5\cdot\log_{10}\left( \dfrac{\sum_{\lambda=380~\textrm{nm}}^{\lambda=500~\textrm{nm}} \left( E(\lambda) \right) }{\sum_{\lambda=380~\textrm{nm}}^{\lambda=780~\textrm{nm}} \left( E(\lambda)\cdot V(\lambda) \right)}\right)

Usage:

[G,ratio] = gindex(lam,spec,threshold)

Where:

Parameter	Description
G	Returns the spectral G-index.
ratio	Optional: returns the actual percentage of the blue part of the spectral power distribution compared to the total power distribution.
lam	Is a vector specifying the spectral wavelengths steps.
spec	Is a vector or row-wise matrix containing the spectral power distribution(s).
threshold	Optional: defines the upper threshold for the calculation, default: 500 nm

Examples:

G-index of CIE LED Illuminant LED-V1:

lam = 380:780;
spec = ciespec(lam,'LED-V1');

G = gindex(lam,spec)

See also: ciespec

Result:

G = 0.8537

G-index of CIE LED illuminants LED-B1 and LED-B5:

lam = 380:780;
spec = ciespec(lam,{'LED-B1','LED-B5'});

G = gindex(lam,spec)

See also: ciespec

Result:

G =

    1.5304
    0.3102

Reference:

Donatello, S., Rodriguez Quintero, R., De Oliveira Gama Caldas, M., Wolf, O., Van Tichelen, P., Van Hoof, V. and Geerken, T., Revision of the EU Green Public Procurement Criteria for Road Lighting and traffic signals, EUR 29631 EN, Publications Office of the European Union, Luxembourg, 2019, ISBN 978-92-79-99077-9, DOI:10.2760/372897, JRC115406.

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