INTRODUCTION TO EVALUATING LIGHTING SOLUTIONS
This brief overview document is intended to provide a high-level summary of the key aspects of an interior lighting solution that need to be considered when evaluating technologies and outcomes. A glossary of common terms is also provided for reference.
LIGHTING PERFORMANCE CONSIDERATIONS
Beginning this overview with lighting performance considerations is done quite deliberately – lighting is a service which allows us to be productive in our built environments, and as such, the most important consideration is that the light has the correct properties to support our day-to-day activities. These requirements obviously vary from environment to environment and depend on the specific tasks being undertaken, so the first step in this process is always to define the task.
The most effective and efficient lighting solution is one that delivers the right amount of the right type of light at the right time and in the right place.
Examining each of these points in more detail points us to a number of guiding principles or regulatory frameworks:
- The right amount… indicates that there is a certain quantity of illuminance required to effectively and safely complete any given task. The guiding standard in this sense is the AS/NZS 1680 series, and specifically the sub-sections of Part 2 which specify the minimum illuminance requirements for interior and workplace environments and the tasks undertaken in those environments.
- The right type… indicates that the light needs to have certain properties to suit the given task, such as appearance and colour properties. Again, the sub-sections of Part 2 of AS/NZS 1680 provide guidance on these requirements across the spectrum of normal tasks/environments.
- The right time… indicates that lighting requirements are very rarely static, and therefore some level of control will be required to tailor the amount and/or type of light to varying needs at different times. At the simplest, this is a matter of being able to switch lighting on and off depending on whether a space is occupied or vacant. At the most complex, this can extend to varying not only the quantity of illuminance (i.e. dimming) but also other factors like the colour properties. Guidance on these considerations is typically found in energy efficiency guidelines or rating frameworks such as GreenStar.
- The right place… indicates that these requirements are specific to definable task areas, but also acknowledges that there are requirements for non-task areas which support good visual comfort and general well-being. Wall and ceiling illumination can be as important for some tasks as the illumination of the task area itself. Implicit in the concept of a ‘right place’ for light is the understanding that there is also a ‘wrong place’ for light as well – this could be in the form of light pollution (unwanted spill of light into the night sky or beyond property boundaries) or glare (obtrusive light being emitted in directions where it causes discomfort or impairs vision).
Best-practice design requires careful consideration of all of these factors, and where applicable, demonstrating compliance with established standards. A summary of some key standards and guidelines is provided in the following section – while it is not exhaustive by any means, it should provide a useful base for reference.
While new technologies have caused considerable disruption in the lighting industry in the past five or so years, it is important to keep in mind that our fundamental requirements from any artificial lighting system have not changed. The technological advances have opened up new possibilities for designers and manufacturers to address a wider spectrum of requirements in a more comprehensive and more efficient manner (as well as opening up new avenues which were previously impossible or impractical), but our needs are still effectively the same.
Standards & Guidelines
While there are several standards relating to lighting and luminaires, it is safe to say that the key reference standard relating to interior lighting is the AS/NZS 1680 series, which contains the following parts and sub-sections:
- Part 0 – Safe movement
- Part 1 – General principals and recommendations
- Part 2 – Specific applications
- 2.1 Circulation spaces and other general areas
- 2.2 Offices and screen-based tasks
- 2.3 Educational and training facilities
- 2.4 Industrial tasks and processes
- 2.5 Hospital and medical tasks
- Part 3 – Measurement, calculation and presentation of photometric data
- Part 4 – Maintenance of electric lighting systems
The table below presents an extract from a few of these sub-sections with recommended illuminance levels for some common interior/office tasks and spaces:
General office tasks involving typing,reading, writing; Computer equipment rooms; Meeting, training rooms etc
|Photocopying and printing rooms; Filing areas etc||240|
|Entrances; Entrance halls, lobbies, foyers, waiting rooms||160|
|Corridors, passageways, ramps||40|
|Staff canteens, cafeteria, dining rooms; Genera||160|
|Kitchens; Food preparation, cooking, washing up||240|
|Storerooms; Medium or fine material requiring care (‘active’ storage)||160|
In terms of overall system performance and efficiency, the GreenStar tool administered by the New Zealand Green Building Council provides targets for best-practice lighting outcomes and awards credits where benchmarks are achieved. These fall under the ‘Indoor Environment Quality’ and ‘Energy’ categories of the GreenStar assessment framework, and relate to specific targets for…
- IEQ11 Electric Lighting Levels - provides target lighting design benchmarks to be achieved
- IEQ-12 Electronic Ballasts - provides some strict requirements on the types of power supply/control components used (with the intention of minimising flicker and ‘hum’ of conventional lighting).
- ENE-4 Lighting - goes hand-in-hand with IEQ11 and focuses on the efficiency of the lighting while still maintaining appropriate lighting performance/service levels.
- ENE-5 Lighting Control - gives increasing levels of credit to lighting control arrangements or systems that can deliver increasing levels of efficiency.
The lighting industry is quickly becoming a technology industry, and the enormous ranges of product offered in the market along with different approaches to presenting data and specifications makes evaluating solutions a complex and time-consuming task, even for industry professionals.
However, a general platform can be established by focusing on several key performance measures and specifications, and that platform can then be used for application specific evaluation and comparison. The following sections outline the basis for that platform (refer to the Terminology section later in the document for more detailed descriptions of the terms).
PERFORMANCE & LONGEVITY
- Luminaire flux - this is the measure of how much light a luminaire produces.
- Luminaire power - this is the measure of how much power is consumed by the luminaire when it is operating.
- Luminaire efficacy - this is the measure of how effective the luminaire is in converting electrical power into useable light.
- Light distribution - this describes the shape/pattern of the light emitted by the luminaire.
- Colour specifications - a combination of factors which describe the appearance of the light (colour temperature), the ability of the light to show colours (colour rendering) and how consistent the colour is from luminaire to luminaire (colour tolerance).
- Lumen maintenance - this describes the rate at which luminous flux reduces over time, and it is expressed in terms of the proportion of flux remaining after a specific period of operation.
- Materials – the materials used in a luminaire’s construction will determine how it will react to certain agents within its environment (i.e. when exposed to UV, chemicals, gasses, marine air etc.)
- Ingress protection – this rating classifies the degree of protection the luminaire has against both solids and liquids trying to enter the enclosure.
- Impact protection – this rating classifies the degree of protection the luminaire has against impact from external objects.
These are the basic specifications for consideration when assessing the technical capabilities of a luminaire and determining whether it will be fit-for-purpose or not. Of course, there are also a number of typical commercial considerations as well – pricing, warranty, track record of the supplier, added-value services etc. – but those are typically specific to each purchaser’s needs, budgets and risk profiles.
For any large commercial or public facility anywhere in New Zealand, a considerable amount of resource is invested every year in operating and maintaining facilities. Depending on the nature of the facility, the costs of operating and maintaining the lighting can be a significant portion of the total costs of operating the facility. To get maximum value from any building asset, the whole life cycle cost from initial capital investment right through to the end of an asset’s service life must be considered.
It is therefore recommended that a total-cost-of-ownership approach is taken to assessing lighting solutions, whether it be in a new-build, refurbishment or retrofit context. Considering that the costs of operating a lighting system (electricity costs and maintenance costs) normally outweigh the purchase cost by a considerable margin, it follows that the best purchasing decisions are normally not the cheapest (up-front) options.
The following ‘glossary’ provides a little extra detail on the specific terms used when discussing lighting and luminaires.
- Illuminance – expressed in lux (lx); describes the amount of luminous flux falling on to (illuminating) a specific surface. One lux is equal to one lumen spread over one square meter (i.e. 1 lm/m2 = 1 lux).
- Uniformity – expressed as a ratio between the average illuminance on a task area/plane and either the maximum or minimum illuminance value on that same area/plane. The most common reference to uniformity is in terms of average (Eavg) and minimum (Emin) illuminances, and this describes how evenly the illuminance is distributed across a discrete area.
- Glare – the presence of bright light (in high contrast to its surrounds) which can either cause discomfort or simply impair vision. In a lighting context, glare is quantified by the Unified Glare Rating (UGR) which is a dimensionless scale with a lower figure indicating less glare. Ratings typically fall within the range of 13 (just perceivable) through to 28 (uncomfortable for extended periods). Office lighting standards typically require a UGR value of 19 or less.
- Luminaire – a complete lighting unit, which typically consists of a light source, some means of
- directing/distributing light, a power supply or converter and connection to a power source, and various mechanical components for mounting and protecting the electrical and optical parts.
- Lamp – refers to a removable/replaceable light source for a conventional luminaire (i.e. incandescent, halogen fluorescent etc.)
- Optic/s – refers in general to the components in a luminaire used to direct and/or distribute light. These can be simple reflectors or diffusers right through to complex micro-lens arrays, and they are typically formed from various types of metals or plastics. As these components modify the raw flux emitted by the light source, their design and the materials used influence the proportion of light lost in reflection and/or refraction, and therefore influence the efficacy of the luminaire as well as the light distribution.
- Driver – refers in general to a power supply/converter unit which receives mains-voltage alternating current power (230-240V AC in New Zealand) and outputs direct current (DC) power at a specified voltage and current suitable for powering LED components. Drivers can be fixed output (meaning the LEDs always operate at full power) or dimmable (meaning the flux from the LEDs can be adjusted). As the power regulator of the luminaire system, the driver is a particularly important component and its reliability is a key factor in overall luminaire service life. Note that the equivalent component in a conventional fluorescent or discharge luminaire was referred to as a ‘ballast’, of which there are two kinds; magnetic and electronic.
- Dimming – refers in general to the capability of adjusting a luminaire’s flux across a range from full power down to a specified minimum (often 10%, but sometimes lower). Dimming can be controlled in a number of ways, but the typical methods used in commercial lighting are DALI (a digital communication protocol), 1-10V (uses a low-voltage analogue signal) or phase/mains dimming (regulates the supply voltage to the luminaire).
- Luminous flux – expressed in lumens (lm); describes the quantity of light (energy) emitted from a light source.
- Luminaire flux – specifically describes the total ‘net’ system luminous flux (including any light losses resulting from reflectors, diffusers and/or lenses), rather than just the gross flux from the light source within that luminaire.
- Input power – expressed in watts (W); describes the total amount of electrical power drawn by the luminaire (which therefore includes any electrical losses/inefficiencies in the luminaire power system).
- Luminaire efficacy – expressed in lumens-per-watt (lm/W); describes the overall effectiveness of the luminaire system in converting electrical power into useable light. It is calculated by dividing the luminaire flux (lm) by the input power (W).
- Luminous intensity distribution – described by intensity distribution curves, which show the luminous intensity of light emitted from the luminaire at various polar angles in all three dimensions. These curves are typically documented by 2D polar plots showing distribution in planes both longitudinal and transverse to the axis of the luminaire.
- Colour temperature – expressed by Correlated Colour Temperature (CCT, in K); describes the colour appearance of light emitted by a light source, relating its colour to the colour of light from a reference source when heated to a particular temperature, measured in degrees Kelvin (K). The CCT rating for a lamp is a general "warmth" or "coolness" measure of its appearance. However, opposite to the temperature scale, lamps with a CCT rating below 3200 K are usually considered "warm" sources, while those with a CCT above 4000 K are usually considered "cool" in appearance. Most commercial lighting is specified as 4000K.
- Colour rendering – expressed by Colour Rendering Index (Ra); describes the degree of colour shift objects undergo when illuminated by the light source as compared with the colour of those same objects when illuminated by a reference source, of comparable colour temperature. The index is a scale between 1 (effectively monochromatic light) and 100 (perfect rendition of all colours). Most commercial lighting requires a CRI of Ra>80.
- Colour tolerance – expressed by MacAdam Ellipses or Standard Deviation of Colour Matching (SDCM); describes the differences in light colour from one LED to another (or one luminaire to another). When LED chips are manufactured, tolerances occur which can result, among other things, in differences in light colour. LEDs are therefore tested after they are manufactured and sorted into tolerance classes. If the colour (chromaticity) coordinates of a set of LEDs all fall within 1 SDCM (or a “1-step MacAdam ellipse”), most people would fail to see any difference in colour. If the colour variation is such that the variation in chromaticity extends to a zone that is twice as big (2 SDCM or a 2-step MacAdam ellipse), you will start to see some colour difference. It is typically accepted that a colour tolerance of 4 SDCM or less for commercial lighting will result in minimal noticeable variations for a casual observer.
- Lumen maintenance – expressed by an ‘Lxx Byy @ zz,000 hours’ rating; defines the rate at which luminous flux depreciates over time. The xx digits refer to the amount of flux ‘maintained’, which is simply 100% minus the proportion of initial flux that has depreciated. The yy digits refer to the proportion of luminaires/light sources within a nominal population that would not meet the xx target flux-specification. So, a luminaire wit a lumen maintenance specification of L80 B10 @ 50,000 hours refers to 20% depreciation (i.e. 80% maintenance) of flux over that 50,000 hours and clarifies that at least 90% of those luminaires would achieve that 80% or greater maintenance specification (i.e. 10% would depreciate by more than 20%). Lumen maintenance specifications must be derived by the industry-standard TM-21 projection method, which uses data from long-term LED testing (LM-80 report, with a minimum of 6,000 hours testing) and in-situ luminaire temperature testing.
- Ingress protection – expressed by an ‘IP##’ rating, where the first digit (from 1 to 6) indicates increasing protection against the ingress of solids/bodies and the second digit (from 1 to 8) indicates increasing protection against the ingress of moisture/water. Simple ‘enclosed’ (i.e. IP20-rated) luminaires are typically adequate for most commercial interior environments, although dust-proof (i.e. IP5X) luminaires typically require less frequent cleaning. Luminaires being used in damp locations (i.e. bathrooms, showers) normally require IP44 ratings or greater, while luminaires in exterior environments normally require IP54 ratings if installed in sheltered locations or IP65 or greater if installed in exposed locations.
- Impact protection – expressed by an ‘IK’ rating from 0 to 10; defines the amount of protection the luminaire has against mechanical impact with varying levels of energy. IK02-rated luminaires are typically adequate for most commercial interior environments, whereas IK08 to IK10 ratings are typically required if there is a possibility of vandalism or likelihood of collision with objects.
- Emergency lighting – refers to lighting that operates in the event of an interruption to the mains power in or around a large building. Requirements for emergency lighting (and the closely associated exit signage) are specified in clauses F6 and F8 of the New Zealand Building Code. Power for emergency lighting can be supplied by either by a centralised battery/UPS, and quick-response generator or individual back-up batteries. The latter is most common in modern fit-outs and is generally regarded as the most cost-effective arrangement to operate and maintain in the long term. Emergency lighting can be provided either by dedicated emergency lighting devices or the capability can be integrated into general lighting luminaires.
Please contact Ecopoint if you require any further information or guidance regarding lighting technologies, design processes and compliance. Ecopoint can assist with assessing lighting requirements, developing fit-for-purpose solutions which minimise total-cost-of-ownership, and building business cases for investment.