Lighting and filters identification

Introduction:

The advent of LEDs has been a game-changer for the lighting industry. Indeed LEDs have already deeply penetrated the automotive and indoor lighting sector and are spreading across various outdoor lighting applications for highways, roadways, bridges, and tunnels. LEDs are slowly but surely replacing sodium lamps, costly metal halides, and halogen lights owing to various advantages such as high efficiency, low maintenance cost, and high lumen output. This paradigm shift calls for new tools for the characterization of such light sources.

 

GoSpectro as a measurement tool for lighting

GoSpectro (Figure 1) is a simple device that can turn any smartphone or tablet equipped with a camera into a compact light spectrometer. In fact this tool enables spectral analysis of light sources, optical filters and various colored objects. This, by measuring emission, absorption, reflection and transmission spectra with unmatched compactness and ease of use. It is the ideal companion for light characterization in the fields or in the lab.

In this application note, we tested GoSpectro on various lamps (LED, halogen, fluocompact, etc) and on optical filters. Sometimes we used the measured spectra to determine the Correlated Color Temperature (CCT) of lights sources and the transmission curve of optical filters.

Figure 1: Picture of the GoSpectro, the ultra-compact
smartphone-based light spectrometer

Light source characterization

We can use GoSpectro to measure the emission spectrum of different types of light sources. The Figure 2 illustrates such emission spectra.

Figure 2: Emission spectra for four
different lighting sources
measured with the GoSpectro

These spectra emission are very specific and we can use it to clearly identify the type of lamp under investigation, even at a far distance. This is particularly useful for the maintenance of street and roadway lighting.

We carried out the tests on halogen lamp and a “cool LED” to try and determine their Correlated Color Temperature (CCT). Using the intensity calibration function available on the GoSpectro application we acquired spectra. Then, from the measured spectra we calculated the CCT :

Figure 3: Determination of the Correlated Color Temperature of a halogen and “cool” LED light

The calculated CCTs are in good agreement with the theoretical values and the spectra show the typical features expected from a halogen lamp (black body) and from an LED light source.

Optical filter characterization

We also used the GoSpectro to measure the optical transmission of three different colored filters. The results were then compared to their reference spectra. The Figure 4 represents the results.

Figure 4: Measurements of three filters optical transmission and comparison to their reference spectra

We obtained good accordance between the experimental spectrum measured on each filter with GoSpectro and the reference spectrum. This confirms we can use GoSpectro for the determination of the optical transmission of optical filters.

Conclusion

GoSpectro enables the identification and characterization of various light sources. Moreover, it can easily measure the spectral response of optical filters in the visible range.

GoSpectro could be a powerful diagnostic tool for the replacement of HID lamps by LEDs lights for various outdoor lighting.