This article is also published on Lighting Management & Maintenance's site.
Written by George McIntyre, Energy Solutions Manager, Acuity Brands
It’s no secret that commercial electricity rates continue to rise. A combination of energy usage and increased demand charges has caused a sharp rise in commercial energy bills. Lighting can often be the largest user of electrical energy, accounting for up to 40 percent in a commercial building. That’s why there’s been a hyper-focus within the commercial and industrial sectors on pursuing energy efficient lighting solutions. This has been especially evident with the advent over the past decade of LED lighting and digital controls, which have proven to deliver significant energy savings compared to conventional lighting.
The good news is today’s lighting solutions deliver exceptional energy efficiency. The not-so good news is, during this aggressive pursuit to maximize energy savings, some key lighting fundamentals, especially around lighting quality, have unnecessarily taken a back seat. However, this does not have to be the case. Lighting solutions can realize both energy efficiency and lighting quality in areas such as visual comfort without making compromises. Here, we will explore how to provide high-quality lighting for a retrofit project while still obtaining exceptional lighting efficiency.
What is Lighting Quality?
Where lighting efficiency refers to the amount of light produced by a lighting system in relation to the amount of energy it consumes, lighting quality refers to the overall appearance and functionality of the lighting system. It takes into consideration factors such as color rendering, color temperature, glare, flicker, and uniformity. A lighting system that factors in quality of lighting can enhance the visual appeal of a space, help improve productivity, and even impact the mood of the occupants in a space.
When specifying a lighting system for a retrofit project, the factors impacting lighting efficiency are often well known and adopted. Efficiency is often measured in lumens per watt (lm/w). The higher the lumens-per-watt rating, the more efficient the lighting system. LED lighting, for instance, is one of the most energy-efficient lighting technologies available, with some models producing up to 200 lumens per watt. The savings are impressive, but the specification process should not stop there when you can extract more value from your lighting system by factoring in lighting quality.
Factors Affecting Lighting Quality
Before jumping into the fundamentals of specifying for lighting and efficiency, here are some key factors in evaluating lighting quality when reviewing fixture specifications. Your lighting fixture manufacturer or representative can assist in determining which factors are most important for a project based on the application and intended occupancy.
- Color temperature: The color temperature of light can affect the mood and atmosphere of a space. For example, warmer color temperatures (around 2700K) can create a cozy and inviting atmosphere, while cooler color temperatures (around 5000K) can create a more energizing and productive atmosphere.
- Color rendering index (CRI): The CRI measures how well a light source renders colors compared to a reference light source of the same color temperature. A higher CRI means that colors will appear more accurate and vibrant. The CRI is calculated based on the performance of the light source across eight color samples (R1-R8) that cover a range of hues, and the R9 value specifically measures the rendering of a saturated red sample. CRI considerations come into play, for example, in a retail environment when displaying color-rich or visually attractive products such as food, clothing, jewelry and so forth, and even in distribution centers when associates need to distinguish product colors when picking discrete items off a shelf.
- Color consistency (binning): Binning refers to the practice of sorting LEDs (light-emitting diodes) into groups based on their spectral characteristics, particularly their color temperature and color rendering index (CRI). A reliable LED manufacturer will often bin their LEDs based on their spectral characteristics. LEDs that fall into the same bin have very similar spectral characteristics, which helps ensure color consistency and quality lighting when the LEDs are used in products like light bulbs, fixtures, or displays.
- Ceiling luminance: Luminance is the measurable quality of light that most closely corresponds to brightness and can be desired in some applications and not in others. For example, a retail store may desire increased ceiling luminance (brightness) so it appears “open” from outside the store. On the (other) hand, in a high-end amenity space, it may be desirable to have zero luminance at the ceiling plane because the focus is on the architecture or other features in the space.
- Glare: Glare can occur when there is a significant contrast between the brightness of the light source and the surrounding environment. Glare can cause general discomfort or even make it difficult for occupants to see properly in a space.
- Uniformity and Light Distribution: Uniformity is how “uniform” or even the light levels are in a space with an objective to avoid variations between darker and lighter areas. Light distribution is the distribution pattern of the light emanating from the fixture. Direct lighting, if not properly specified, can create harsh shadows and hot spots, while indirect lighting can create a more diffused and even distribution of light. Uniformity and light distribution are factors for lighting throughout the space including ceilings, walls, vertical surfaces (such as tables and desks), and hallways/corridors.
- Flicker: Flicker occurs when the light source rapidly turns on and off. This can cause eye strain, headaches, and even seizures in some individuals. To find low flicker fixtures, customers can look for products that have been certified or tested for flicker by reputable third-party organizations (see Federal Projects UFC/P100 and the IEEE’s P1789 Standard.)
- Maintenance: Proper maintenance of lighting fixtures is important to ensure that they are functioning at their best. Dirty, dusty, or damaged fixtures can decrease lighting quality and efficiency.
Focus on Lighting Fundamentals
When specifying a lighting solution, there are several key lighting fundamentals – including data about energy usage and lighting quality – to focus on when selecting lighting fixtures and related technology. These fundamentals help keep the objectives of lighting a space in the forefront and help in obtaining lighting efficiency without sacrificing lighting quality.
Deliver the correct amount of light for the space and task.
The amount of light required for each space and task in a commercial setting depends on various factors such as the nature of the work being done, the age of the occupants, the size of the space, and the type of lighting fixtures being used. Here are some general guidelines based on foot candle recommendations as listed by the Illuminating Engineering Society:
- General lighting: For general lighting in offices, schools, warehouses, industrial spaces and other commercial spaces, a lighting level of around 30 to 50 footcandle is recommended. Footcandle is the unit of measurement for the amount of light that falls on a surface. The exact amount of light needed may vary based on factors such as the age of the occupants and the size of the space.
- Task lighting: For tasks within a space that require more focused lighting, such as reading or detailed work, a lighting level of around 75 - 100 footcandle is recommended. This can be achieved using task lamps or fixtures that are specifically designed for task lighting.
- Conference rooms and presentation areas: These spaces may require higher levels of lighting to accommodate visual aids such as projectors or whiteboards. A lighting level of around 50 - 75 footcandle is recommended for these spaces.
- Restrooms and hallways: These areas typically require lower levels of lighting, around 10 - 20 footcandle.
- Retail spaces: Retail spaces may require higher levels of lighting to showcase merchandise. Lighting levels of around 75 - 150 footcandle are recommended for these spaces.
It's important to note that lighting levels can also be affected by factors such as the color of walls and surfaces, the amount of natural light in a space, and the type of lighting fixtures being used. A lighting designer or a qualified electrician can help determine the appropriate lighting levels for each space in a commercial setting.
Distribute the light evenly where and when it is needed.
Distributing light evenly where and when it is needed involves designing and positioning lighting fixtures in a way that provides the appropriate amount of light to the intended space or task. Here are some key factors to consider when aiming for even light distribution:
- Task and space requirements: Different spaces and tasks require different levels and types of lighting. Understanding the needs of the space or task is important in determining the appropriate lighting design.
- Lighting layout: The layout of lighting fixtures is important in achieving even light distribution. The fixtures should be positioned in a way that ensures the light is evenly distributed throughout a space.
- Lighting intensity: The intensity of the light should be appropriate for the space and task. Too much or too little light can create problems such as glare, eye strain, or inadequate illumination.
- Light color temperature: The color temperature of the light can affect the ambiance of the space and the visibility of objects. Choosing the appropriate color temperature can help to achieve the desired effect.
- Control systems: Lighting control systems such as dimmers or timers can be used to adjust to the proper lighting level where the light is required or desired based on the needs of the space or task. This is in addition to what control systems can do to improve lighting efficiency.
In summary, achieving uniform, even light distribution requires careful planning and consideration of the needs of the space or task, as well as the appropriate lighting layout, intensity, color temperature, and control systems. Again, a lighting designer or a qualified electrician can help to create a lighting plan that achieves the proper light level when and where it is needed in a commercial setting.
Evaluate lighting fixture service life
The service life of a lighting fixture can vary depending on various factors such as the quality of the fixture, the frequency of use, and the environment in which it is used. With proper selection and maintenance, a lighting fixture can typically last anywhere from 10-20 years.
Periodic maintenance is important to ensure that the lighting fixture continues to operate at optimal performance and to extend its service life. Maintenance tasks may include cleaning the fixture, replacing drivers, inspecting for damage or wear and tear, and confirming controls operations are still in line with current user application.
Lumen Maintenance (in contrast to initial lumens often stated at installation) is about how a long a fixture maintains the desired lumens and light output to provide the correct amount of light over the life of the system efficiently, which is key factor when evaluating lighting fixtures. L70 and L90 are terms used to describe the lifespan of a lighting fixture, and they refer to the amount of time it takes for the light output of the fixture to degrade to a certain percentage of its initial brightness. For example, L70 of 100K to 150K means a fixture will maintain a minimum of 70% of the luminous flux for a defined period (in this case, 100,000 to 150,000 hours) before degrading below that percentage.
When comparing a lighting fixture with an L70 of 100K to 150K from a reliable manufacturer vs. 50K hours (which is often seen with replacement LED tubes) means that fixture will have less degradation over the same period allowing for either reduced wattage, increased service life, or both. Selecting fixtures with poor lumen maintenance forces a customer to re-do an installation sooner than planned or endure lower than expected light levels until the fixture eventually needs to be replaced.
Focus Equally on Lighting Efficiency and Quality
The concept of lighting efficiency and lighting quality are two crucial aspects to be considered in lighting design. A focus on both aspects is necessary if the objective is to create an optimal lighting environment that is efficient, comfortable, and aesthetically pleasing.
Using the right lighting and control solution can enhance the comfort, productivity, safety, and security of a given building or facility space. The right LED technology and enhanced controls can help meet code compliance and deliver energy efficiency and reduce operating budgets while offering visual comfort and lighting quality for occupants over the expected life of the system.
For more information on Acuity Brands Retrofit products, tools and resources, please visit the Retrofit Solutions website: www.acuitybrands.com/retrofit
