The effects of lighting have a significant impact on human productivity, psychology, and mood. The challenge in lighting design is to create an illuminated environment that supports human activity while being equal parts ergonomic, aesthetic, and energy efficient. Some of these characteristics are more important than others in a given environment. The design priority for each lighting application is guided predominantly by the type of activity that is expected to occur in the environment, with the goal of enhancing the efficiency of this activity. For instance, lighting for manufacturing facilities is primarily driven at saving cost for the owning business or property manager, while lighting for a medical lab has an ergonomic goal of providing enough light to perform critical visual tasks. Where aesthetic is a primary concern for enhancing human experience and mood – as in hotels, museums, and entertainment facilities – lighting geometries and colors may be less geared toward ergonomics and focus on overall sensory impact. A blend of these objectives tends to occur in office environments, where visibility is necessary for productivity (requiring ergonomic lighting), which may also be affected by human mood (requiring aesthetic lighting), but the building lessee is also concerned with cost-savings (requiring energy-efficient lighting).
Achieving the desired effect through lighting design requires extensive measurement of lamps, luminaires, and other light sources to adjust for the photometric characteristics of each light, which differ for incandescent lamps to fluorescents to LEDs. Understanding these characteristics enables the design to meet the desired emission angles, colors, reflections, contrast, and patterns for a given space.
Radiant solutions for lighting include photometric light and color measurement technology—from goniometric systems, which measure light as a factor of angle, to non-goniometric systems, which measure overall illumination patterns. These systems can be applied in lighting design and quality control to accomplish all phases of lighting development from light source characterization to production. Radiant’s measurement solutions for lighting design capture complete and precise three-dimensional spatial measurements of a light source’s output (creating standard IES, EULUMDAT (LDT), and Radiant Source Model™ (RSM) files), which can be exported for use within lighting design software. Radiant’s solutions for quality control of light sources during production include ProMetric® Imaging Colorimeters and Photometers to ensure manufactured lighting meets design specifications.
Lighting for Ergonomic Purposes
Fundamentally, electric lighting has a practical purpose – it is meant to enable human activity at all times, regardless of the ambient or daylight conditions. In some environments, ergonomics is the most important aspect of lighting design. For instance, lighting in an airplane cockpit must be sufficiently bright and correctly distributed to allow a pilot to see important instruments as he flies. Commercial lighting must evenly illuminate an office space and reduce glare to allow workers to easily accomplish their tasks. Radiant offers both near-field and far-field methods for measuring luminous intensity and illuminance distribution, as well as a light source’s Unified Glare Rating (UGR), to ensure that brightness, beam patterns, and glare are accurately defined for the optimal ergonomic design.
Beyond brightness and illuminance distribution, color also plays an unsung but critical role in lighting ergonomics. In an operating room, bright light is imperative for visibility during surgical operations. However, the color of light is equally important in this space. The color rendering of organs and tissues under various lighting colors and temperatures can affect a surgeon’s ability to visually distinguish color differences that indicate tissues types and tissue health. Radiant light measurement systems measure a light’s Correlated Color Temperature (CCT) over angle to determine a source’s temperature from cool to warm, which may innately enhance object colors when viewed under the light. Based on the configuration, Radiant systems can also extrapolate Color Rendering Index (CRI) values (as well as CIELAB values) which can help to determine how natural colors appear under the light source.
Lighting for Aesthetic Purposes
Lighting design for aesthetics focuses on patterns and colors that enhance an environment, even regardless of ergonomic impact. Hotels, restaurants, entertainment spaces, and retail environments employ lighting designs that attract their clientele through the use of warm and engaging angles and colors. Luminance, chromaticity, luminance distribution patterns, as well as a light’s CCT and CRI, can be varied artistically and strategically to create an environment that evokes the desired mood. Lighting designers may also employ layers of lighting, each having their own unique photometric features, from ambient room lighting to accent and decorative lighting, which require different measurement criteria.
Radiant’s goniometric and non-goniometric systems can be used to measure lamps and luminaires for aesthetic lighting design. For each layer of lighting, there may be an ideal measurement method to acquire the necessary data. In accent lighting, luminance (Lv), chromaticity (Cx ,Cy or u’,v’), and luminous intensity are often the primary focus of design—since the light source will produce more targeted, intense illumination patterns. When designing ambient lighting, the goal shifts to measuring the illuminance distribution of light to ensure the intended illumination against a surface or large area, while ensuring low glare. In these applications, a near-field goniometric measurement system may be employed to achieve all required measurements of the source.
Lighting for Energy Efficiency
When conserving cost and energy is a priority, there are several approaches that can be taken to increase efficiency in lighting design. Primarily, a designer should consider the lamp that is used, whether incandescent, fluorescent, or LED. The light-output-to-energy-usage ratio varies between lamps, and each must be measured accordingly. Beyond lamp type, designers may use layering techniques to optimize energy efficiency while maintaining adequate light levels within a space. Illuminance (measured in lux or foot-candles) is measures the appearance of light on a surface.
In a layered lighting design, designers can save energy by varying the level of illuminance produced by the different layers of light – from ambient lighting (usually 300-500 lux, or roughly 30-50 foot-candles) to accent lighting (1500-5500 lux, or roughly 150-500 foot-candles) to task lighting (500-2000 lux, or roughly 50-200 foot-candles—depending on the task). Radiant’s light measurement systems capture illuminance using far-field measurement techniques that employ a ProMetric Imaging Colorimeter or Photometer. In this type of application, the ProMetric imaging system is mounted on a tripod and positioned facing an illuminated surface to measure light cast on a wall or through a diffuser. This allows the imaging system to capture both the illuminance distribution as well as calculate the luminous intensity of the light source from a single measurement. This measurement technique can be applied in the lab or during production within a designated measurement space on the line.
Radiant Solutions for Light Source Characterization
Radiant light measurement systems include goniometric and non-goniometric systems for modeling light sources for design and measuring for quality control. The choice to perform light measurement using either a goniometric or non-goniometric system comes down to restrictions on measurement space, and the scope of the measurement data to be acquired. Radiant’s goniometric and non-goniometric solutions are outlined below.
Goniometric: Near-Field Measurement
Radiant goniometric solutions employ a goniometer (SIG-400 for LEDs and small luminaires, or PM-NFMS™ for small to large luminaires) to model a light source using near-field measurement methods. These systems measure the luminance (Lv) and intensity distribution (candela) of the source, accounting for the spatial origin and angle at which the light is emitting—providing a complete understanding of the light source’s output as seen at any distance. Because these imaging systems measure the precise spatial position and angle of the light source, the dimensions of the light source (for instance, an LED strip) influence the illumination pattern and therefore affect the measurement data.
Goniometric systems generate ray set data to quickly output IES, EULUMDAT (LDT), and Radiant Source Model™ (RSM) files (or, luminance data for measuring glare). Beneficial for lighting design, IES, LDT, and RSM files can be exported into common optical design ray-tracing software (such as ASAP®, FRED ®, LightTools®, LucidShape®, Opticad®, OSLO®, OpticStudio™ (ZEMAX), SimuLux®, SPEOS®, TracePro®, Photopia™, and IES TM-25).
Features of a near-field measurement system:
- Combines a goniometric system (such as a Radiant goniometer) with an imaging colorimeter or photometer (such as a Radiant ProMetric imaging system)
- Models the complete spatial and angular output of a light source
- Takes approximately 1,500 measurements to output a complete characterization
- Requires limited measurement space (<5m)
- Can be used to extrapolate far-field distribution (or ray-traced) data from Radiant Source Model (RSM) files
An example of a goniometric system employing the PM-NFMS near-field measurement system and a ProMetric Imaging Colorimeter to measure the complete spatial output of a large light source at a given angle.
Non-Goniometric: Far-Field Measurement
Radiant’s non-goniometric solutions employ an imaging colorimeter or photometer to measure a source using far-field measurement methods. These systems measure luminous intensity (cd), which is the luminous flux (lm) in a given direction. A far-field measurement system measures the beam pattern cast by a light source, so the dimensions of the luminaire itself (for instance, an LED strip) do not influence the measurement data the way they do in near-field measurement scenarios.
Non-goniometric systems generate IES files for lighting design and bitmap files (captured by imaging systems). Beneficial for lighting design, IES files can be exported into common optical design ray-tracing software (such as ASAP®, FRED ®, LightTools®, LucidShape®, Opticad®, OSLO®, OpticStudio™ (ZEMAX), SimuLux®, SPEOS®, TracePro®, Photopia™, and IES TM-25).
Features of a far-field measurement system:
- Uses only an imaging colorimeter or photometer
- Measures illumination distribution (beam pattern) of any light source (size of the source has no influence on the measurement of the light pattern)
- Takes a single measurement to output a complete characterization of the source
- Can be used for quality assurance in high-volume manufacturing operations
- Light can be cast against a wall or screen to measure light (reflection of the source)
- Measure light through a diffuser (transmission of the source)
Examples of non-goniometric measurement methods using an imaging colorimeter to measure the beam pattern of a light source reflected off a wall or screen (left), or through a diffuser (right).
Radiant Solution Comparison: Light Source Measurement Systems
|Near- or Far-Field||Solution||Measurement Method||Data Sets||File Output||Typical Space Required||Typical Measurement Time||Typical Applications|
|Goniometric||Near-Field||SIG-400 (Source Imaging Goniometer™)||The imaging system is rotated relative to the light source, capturing measurements of the source at all angles.||< 2 m||1-4 hours||Light source modeling for lab and R&D applications.|
|PM-NFMS™ (ProMetric® Near-Field Measurement System)||The light source is rotated relative to the imaging system, capturing measurements of the source at all angles.||< 7 m|
|Non-Goniometric||Far-Field||ProMetric® Imaging System||Light from the source is cast on a wall or screen and measured by an imaging colorimeter or photometer||~10X size of the light source||1-2 sec||Qualification of small to large light sources, either in the lab or in production settings|
Radiant Solutions for Production-Level Testing
Light sources and luminaires are manufactured to precisely replicate the design specifications for color, luminance, luminous intensity, and other measurements of the original lighting design. Radiant ProMetric Imaging Colorimeters and Photometers combine the accuracy of sophisticated optical filters with patented ProMetric calibration technology to provide complete measurement data in a single image. These systems leverage the speed and space-efficiency of a compact CCD-based system, ideal for high-volume production lines and are capable of measuring hundreds or thousands of small light sources (such as LEDs) simultaneously.
Radiant TrueTest™ Software measures an LED array for intensity and color during in-line quality inspection.
For large lamps and luminaires, a ProMetric imaging system can be employed in-line to measure light from each source that is cast onto a wall or through a diffuser as the light source passes. This far-field (non-goniometric) method ensures accurate luminance, chromaticity, and illuminance distribution data for each manufactured device without delaying production to take each measurement.
Webinar: Creating IES Files for Luminaires and Lighting Fixtures
Webinar: Improving Color Measurement Accuracy for LED, Luminaire, and Display Imaging
Presentation: Near-Field Testing of Luminaires
White Paper: Efficient Measurement of Large Light Source Near-Field Color and Luminance Distributions for Optical Design and Simulation