The advent of technology advances in LED lighting has brought enormous choice in terms of light quality, control and energy efficiency. However, LED lighting is a very different light source compared with traditional lighting. Facility Managers, lighting installers, specifiers and lighting designers alike are now faced with spending more time in product selection and validation. The Asensetek Lighting Passport, a commercial lighting spectrometer is a convenient, affordable, reliable scientific tool to make accurate measurements of lighting performance.
The Asensetek Lighting Passport spectrometer combined with the SGM APP is a powerful tool capable of making a broad array of lighting measurements. These core metrics are indispensable to anyone wishing to obtain a definitive understanding of any light source.
Illuminance is a measure of how much luminous flux is spread over a given area. One can think of luminous flux (measured in lumens) as a measure of the total “amount” of visible light present. Illuminance is a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area. Illuminance is inversely proportional to area when the luminous flux is held constant.
The CCT or Correlated Colour Temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. Colour temperature is conventionally expressed in degrees Kelvin (K). The higher the colour temperature, the “cooler”the light will appear.
Chromaticity is an objective specification of the quality of a colour regardless of its luminance. Chromaticity consists of two independent parameters, often specified as hue (h) and saturation (s) or “colourfulness”. The CIE 1931 xy chromaticity space is shown here depicting the chromaticities of black-body light sources of various temperatures, and lines of constant correlated colour temperature
Colour rendering index (CRI)
is a quantitative measure of the ability of a light source to reveal the colours of various objects faithfully in comparison with an ideal or natural light source. Light sources with a high CRI are desirable in colour-critical applications.
Lux, CRI, CCT and Chromaticity are fundamental light source attributes. Knowledge of these parameters are critical considerations when designing a lighting installation or verifying performance. This is especially helpful after installation as well as in years to come; for example, when assessing compliance to lighting manufacturers’ performance guarantees.
The CIE1931 System
Colour as described in the CIE1931 system can be plotted on a chromaticity diagram as a plot of the chromaticity coordinates x and y. The black line indicates the locus of an ideal “black-body” radiator. Points along the black body curve are at different colour temperatures (CCT) but at the same “chromaticity” as an ideal or natural source.
Colour variation and SDCM
The colour variation of a source can be measured by the number of standard deviations of colour matching (SDCM). A colour difference of 1 SD is not visible to human observers and 2 to 4 SD is barely visible. However, if light sources differ by 5 or more SD the difference is readily noticeable. SDCM is a powerful tool for quantifing colour differences in light sources that are allegedly supplied as having the “same” colour as well as checking light sources over time to quantify any shift in colour.
R1-R15 provides a quantifiable metric (0-100) to describe the colour rendering ability of a light source to reveal the colour appearance of objects faithfully when compared with an ideal reference or natural light source. In this example, R9 = 45, which indicates that red tones will be rendered very inaccurately when illuminated by this light source.
R1-R15 can be plotted either as histogram or a radar chart.
TM-30 is a new way to measure colour rendering that is set to replace the traditional CRI method which has come under increased criticism for its inability to accurately describe how well LEDs render colours. For example, an LED can have a relatively high CRI but render red badly. TM-30 is based on a reference set of colour samples that is more representative of objects in the real world than the pastel samples used for the CRI method.
Taking a measurement
Measurement takes between 6 to 16 seconds, after which the user is presented with a list of their pre-selected metrics in a clear, easy to read format.
accessing the data plots is achieved simply by swiping.