Many of the products and services we use or consume have a unit of measurement. Kilograms, litters, meters, kilowatts, gigabytes and...lumens.
All except lumens have one important thing in common: interested people have easy access to devices of measurement. Crucial for quality control or fairness of a transaction.
Weighted scale, tape measure, a hand watch, plug in energy meters or a simple piece of software. All can be purchased by most people, even with a few dollars and a trip to a store nearby.
Lighting is one of the few markets where consumers can find it difficult to measure the lumens and other relevant units (candela, degrees kelvin, lux, nanometers). To do the most basic quality control. It gets even more complicated with CRI, TM-30, CQS scores, CIE1931 or spectrometer graphs.
Many of the above measurements are made in a photo metric laboratory with measurement apparatus worth tens of thousands of € and qualified professionals.
The lamp or lamps to be measured must be physically shipped to such a laboratory, a process that has shipping costs and that can take days or weeks to complete. The measurement results, a digital file with numbers and graphs, can cost hundreds or thousands of euros.
To set up such a laboratory is also not as simple as buying the equipment and finding the staff to operate it. Measurements standards must be implemented, and an international accreditation has to be obtained. Without these, the measurements obtained might be seen with the same trust as a Word document with data invented from someone's imagination. Thus, a good accredited laboratory might not even present in your own country, adding a language barrier to the set of already exists hurdles for a measurement of lighting.
With this situation, manufacturers of LED lighting should provide complete and trustworthy technical information of their products and professionals & sellers should come to the aid when the above is missing or unclear.
Without professionals & sellers to help, the consumer is left only with simple questions such as:
Does the manufacturer seem trustworthy?
Is the exhibition booth looking professional?
Isn't the product to low cost for the advertised specifications it has?
Do I like the website I am viewing the product on?
Are those pictures in the seller portfolio actually his own projects? If they are, should I trust the other customer's decisions?...
... Where is my portable lie detector?
There must be a better way...
Professionals & sellers should invest time and energy to build up the knowledge base required to buy lighting products in the optimum way and share as much as this info as possible.
They should also invest in the ability to measure lighting with a portable measuring device.
First, let's review briefly what should be needed to measure. The many units related to lighting can be classified in three categories:
Brightness:
Total light emitted by a light source = Luminous Flux, measured in lumen.
Light where you need it = Illuminance which is the total luminous flux that reaches a surface (for example your desk), per unit area. It is measured in lux.
Total lighting from flat, diffuse surfaces = Luminance, measured in candela per square metre (cd/m2). The most common use of this measurement is for the LCD/OLED displays found in all electronic devices, from smartphones to computers
Total light emitted by a focused light source in a particular direction per unit solid angle = Luminous Intenstiy, measured in candela (cd). This is a useful measurement for directive lighting elements such as reflectors.
Spectrum:
Can the light source match natural light in terms of the ability to reproduce colors? Answered with a score up to 100 (the best) by methods such as CRI and TM-30-15
Natural daylight is dynamic, based on the time of day, location on earth and weather patterns. This is quantified in the form of color temperature, with an example below.
Most artificial light sources have a fixed color temperature. Choosing the one for an indoor or outdoor space is determined by many factors, from activity to mood.
Does the light flicker?
Light flicker refers to rapid, repeated changes in light intensity - light that appears to flutter and be unsteady. It is caused when the voltage supplied to a light source changes or when the power line voltage itself fluctuates. Sever flicker can cause headaches, eye strain and general eye discomfort. In many cases, people that have such symptoms do not attribute them to the lighting used.
With a hand held spectrometer, measurement and quality control of light sources of finally possible and accessible. For the optimum way to buy lighting.
CRI, Color temperature, Flicker (Quality) for comparison with manufacturer presented data and industry standards.
Spectrum diagram, Peak Wavelength (λp), CIE 1931 and CIE 1976 (Research related) for comparison with manufacturer data or for special research or design purposes.
A hand held spectrometer is similar to a smartphone, with the added sensor and special software. It will measure and display most of the quality, quantity and research related data of the analyzed light source and can even offer an export function to the PC for more detailed analysis and record keeping.
Everything is done on location, wherever the spectrometer is placed. Control is made via an app that runs on the device, usually with a user-friendly design easy to understand by most.
The measurement results can be simple numbers, or charts & graphs in various standard formats. Common are the spectrum diagram, Peak Wavelength (λp), CIE 1931 and CIE 1976.
Luminous Flux (lumen) measurement
Total light emitted by a light source = Luminous Flux, measured in lumen, is not possible to measure outside a laboratory for most lamps. It requires an integrated sphere or goniometer that cannot be miniaturized or easily made portable.
However, including Illuminance data with every lamp or luminaire data sheet will help independent quality testing via a hand held spectrometer.
For larger scale lighting you can use the free software Dialux to design, calculate and visualize light professionally - single rooms whole floors, buildings and outdoor scenes. You can then compare the simulations results with actual measurements from your handheld device.
However, in some cases the lighting manufacturer does not provide the files for Dialux to use for its calculations.
A simple, free to use app with the basic space design, measurement functions of Dialux and generic models of luminaries (with user editable values for luminous flux, color temperature and view angle) could make possible further independent quality testing, especially for luminaries at the low price end of the market that have come with very little data.
