DESIGN PRINCIPLES FOR LIGHTED MIRRORS

Transcription

1 DESIGN PRINCIPLES FOR LIGHTED MIRRORS Author: George Wahlgren

2 Design Principles for LIGHTED MIRRORS AUTHOR GEORGE WAHLGREN Director of Product Development Robern In this paper, we will detail critical factors in selecting and specifying bathroom mirror lighting, focusing on lighted mirrors that integrate LED lighting. By the end of this paper, you will understand light output and brightness, color rendering and temperature, aesthetics, the LED source, dimming, and exciting new options such as color control and touch interfaces. You will be able to select a lighted mirror with a full understanding of its performance, which may result in more satisfied clients. 1 / Design Principles for Lighted Mirrors

3 ROBERN TOPICS 1 INTRODUCTION Whether in a home or commercial building, the bathroom serves as both grooming station and refuge. Much of the time we see ourselves is in front of bathroom mirrors. A 2014 Today/AOL Ideal to Real body image survey found that adult female respondents spent an average 55 minutes per day on their appearance while adult male respondents spent an average 39 minutes. The lighting, therefore, should: Produce sufficient illumination (light level) for tasks Produce sufficient brightness for visibility without glare; Make users look their best, properly modeling (visually rendering) the face without unflattering shadows; and Enhance the space appearance Achieving the above necessitates task lighting dedicated to the bathroom vanity. The primary factors involved in selecting mirror lighting include: Physical: light source, form factor, placement, and aesthetics Light: light output and emission pattern Color: color temperature and rendering Control: ON/OFF, intensity, and color temperature (tuning) Energy: energy efficiency TRADITIONAL MIRROR LIGHTING Traditionally, dedicated mirror lighting used incandescent and halogen lamps, typically necessitating installation of the mirror and its lighting as separate items. Today, these lamps may be replaced with more-efficient compact fluorescent or LED lamps, though the form factors are similar. A typical design scheme for small mirrors might include decorative wall-mounted luminaires (light fixtures) placed on each side, providing even and shadow-free facial lighting. The American Lighting Association recommends mounting these luminaires at least 28 inches apart and 60 inches off the floor. For large mirrors, a typical design scheme might include a horizontal strip of vanity lights mounted above the mirror, about 78 inches off the floor. The lamps (bulbs) should be highly diffuse, such as decorative globes, or shaded. Adding a dimmer allows users to control visual comfort and ambiance. Design Principles for Lighted Mirrors / 2

4 INTEGRATED LED MIRROR LIGHTING The advent of the light-emitting diode (LED) light source offers extraordinary design potential for mirror task lighting. LEDs are bright, directional, and long-life light sources that emit very little radiated heat and are relatively resistant to shock and vibration. They are also highly compact, providing manufacturers greater design freedom to produce fully integrated, aesthetically pleasing mirrors and mirrored cabinets. Lighted mirrors are available in various configurations. A popular approach is to etch a pattern in the glass from the reverse side, which makes the front easier to clean, and integrate a diffuser backlit by an LED assembly. While decorative and even customized etchings are available, the most popular designs are classic lines and circles constituting perimeter light borders or inset light bands or borders, as shown in Figures 1.1 and 1.2. This approach delivers an upscale and pleasing aesthetic defined by clean bands or circles of light, integrated with no visible lamps or lighting hardware. Additional edge lighting, either white or colored, can accent the mirror. The selected product should provide this integrated functionality while maintaining a slim profile. Manufacturers typically rate lighted mirrors at 50,000 hours of service life. This value is an estimate for an average product based on a combination of standardized testing and manufacturer experience. It expresses a point in operating life at which light output has Figure 1.1 Figure 1.2 Bulb Comparison INCANDESCENT 1,000 hours FLUORESCENT 3,000 hours HALOGEN 8,000 hours LED 50,500 hours 3 / Design Principles for Lighted Mirrors

5 ROBERN TOPICS 1 gradually declined to 70 percent of its original light output, lumen depreciation being considered the primary failure mode. As another failure mode is driver failure, which may occur before 50,000 hours, designers should confirm the lighted mirror uses a high-quality driver as well as ensure that the driver is serviceable. LIGHT OUTPUT AND BRIGHTNESS A luminaire s light output defines the quantity of light exiting it, measured in lumens. An example 40-inch light band in a lighted mirror may emit 800 lumens, approximating the output of a 60W incandescent lamp (860 lumens). Manufacturers offer a range of light output to satisfy different applications. With bathroom task lighting, the task is relatively fixed. The user typically stands 18 inches from the mirror s center. The lighted mirror should produce satisfactory illumination on the user s face at this distance. In residential applications, the designer may provide a higher level, which users can adjust to their visual needs using a dimmer. This offers a choice of soft ambient or bright task lighting achieved via smooth, continuous dimming. Light should strike the face from at least two directions ideally, from the sides which provides even illumination and proper modeling with minimal shadows. The face should become bright enough for good visibility, while the light source should be soft and diffuse to avoid discomfort caused by glare, particularly if the source is within the user s cone of vision (about 60 degrees). Color temperature WARM LIGHTING COOL LIGHTING Design Principles for Lighted Mirrors / 4

6 COLOR TEMPERATURE AND RENDERING The lighting industry relies on metrics to describe the color characteristics of light sources. The most popular are correlated color temperature (CCT) and color rendering index (CRI). CCT, measured in kelvins, describes the color appearance of light relative to an ideal reference light source. Common for incandescent lamps, a 2700K CCT is visually warm, enhancing reds and oranges while connoting a more intimate atmosphere. A 4000K CCT is warm-white, enhancing blues and greens while connoting a more public atmosphere. The right choice depends entirely on user preference. Residential bathroom lighting is typically warm in color appearance. As many people transition from home to workplaces lighted using fluorescent and other cooler-cct light sources, ideally, LED lighted mirrors will provide flexibility to examine one s appearance under both warm- and neutralwhite CCTs. New control methods take advantage of LED color characteristics to offer users the ability to adjust CCT either using a wall controller or, depending on the product, via an interface integrated with the lighted mirror itself. Another popular metric is color rendering index (CRI), which describes how closely the light source renders colors compared to an ideal reference source with the same CCT. It averages color rendering for eight color samples (R1 through R8) that are light in saturation. Manufacturers may test another six colors, including R9 through R12, which are saturated colors. These don t contribute to CRI, though some manufacturers report R9, which is a saturated red, to demonstrate their source effectively renders skin tones and reds commonly found in retail and similar applications. The CRI scale has a maximum value of 100; halogen lamps and daylight have a CRI of 100, while incandescent lamps are near 100 CRI. For bathroom lighting, a higher CRI is particularly desirable to bring out skin tones and enable users to match makeup closely to skin tone. For LED lighting, CRI should be 90+ to render colors as effectively as possible and make users look their best, with an R9 value of 50 or higher. Figure K Warm White 5600K Cloudy Sky 4000K Cool White 10000K Bright Sun/ Blue Sky 5 / Design Principles for Lighted Mirrors

7 ROBERN TOPICS 1 CRI (Color Rendring Index) 90 CRI 50 CRI CONTROLS Lighting controls provide the functions of ON/OFF, dimming, and CCT control. ON/OFF: In many residences, a simple manual switch is sufficient for ON/OFF control, though California s Title 24 energy code requires at least one luminaire in bathrooms to be controlled by a vacancy sensor. In this case, users activate the lights using a manual switch. The sensor automatically turns the lights OFF based on occupancy. In commercial buildings, meanwhile, the majority of energy codes require vacancy or partial- ON occupancy sensors in lavatories to reduce energy consumption. Dimming: In residential bathrooms, dimmer-switches can provide both an amenity and means of saving energy. A dimmer allows users to adjust lighting intensity to preference across a wide range. The effect should be smooth continuous dimming without: Flicker: visible light modulation Shimmer: small fluctuation in light output Pop ON: the lights fail to turn ON until the dimmer reaches a higher setting, at which point they turn ON at the higher light level Drop out or OFF: the lights turn OFF before the dimmer reaches its lowest setting A line-voltage (phase-cut) dimmer may prove sufficient, though the designer should confirm specific compatibility between any LED lighting product and the dimmer to minimize potential for performance issues. One method of ensuring compatibility is to specify LED products and wallbox dimmers that are compliant with the NEMA SSL-7A standard. An alternative is to specify a lighted mirror featuring an onboard dimmer- Design Principles for Lighted Mirrors / 6

8 switch. This premium feature allows the user to access smooth continuous dimming using a capacitive touch point, as shown in Figure 1.4. Because the manufacturer packages and tests the dimmer and light source as a system, the user is assured of smooth continuous dimming with no performance issues. Besides ON/OFF and intensity, CCT control is now becoming increasingly available with LED products. With the majority of products, independent dimming of dual arrays of warm-and cool-white LEDs produce a choice of warm (e.g., 2700k) and cool (e.g., 5600K) CCTs. This provides flexibility to adapt vanity lighting to different uses and an attractive amenity. Implementing CCT control often requires system integration but can also be accomplished with a specialized controller packaged with the lighted mirror. If the manufacturer requires low-voltage wiring to communicate between a wall controller and the controller at the mirror, wiring installation must be factored into the cost. Some manufacturers accomplish this through wireless communication and apps. Figure 1.4 CALIFORNIA TITLE 24 California s Title is the most robust commercial and residential energy code in the country. Relevant residential code requirements include: All lighting must be high-efficacy (>45 lumens/w). At least one luminaire in bathrooms must be controlled by a vacancy sensor and otherwise all LED luminaires controlled by a vacancy sensor or dimmer. Wallbox dimmers intended to control LED lighting must be SSL-7A compliant. All LED lighting must be >90 CRI (with an R9 of >50) and capable of producing a CCT of <4000K. CIRCADIAN LIGHTING Light is foundational to vision but can also influence well-being, notably nonvisual effects on the body s circadian system via the daily change from light to dark. The circadian system produces and regulates bodily functions such as the sleep-wake cycle based on circadian rhythms, or 24-hour cycles. According to the Lighting Research Center, four primary factors affect how light influences the circadian system. These include quantity of light falling on the eye s photoreceptors (vertical illumination), spectrum (spectral power distribution), timing, and duration. Lighted mirrors are potentially influential by enabling adjustment of both light output and CCT at influential times of the day. In the morning, the lighted mirror can be adjusted to its maximum 7 / Design Principles for Lighted Mirrors

9 ROBERN TOPICS 1 Circadian rhythms (24-hour cycles) High alertness 10:00 Highest testosterone secretion 09:00 Bowel movement likely 08:30 Melatonin secretion stops 07:45 Sharpest rise in blood pressure 06:45 06:00 Lowest body temperature 04:30 12:00 14:30 Best coordination 15:30 Fastest reaction time 17:00 Greatest cardiovascular efficiency and muscle strength 18:00 18:30 Highest blood pressure 19:00 Highest body temperature Deepest sleep 02:00 24:00 21:00 Melatonin secretion starts 23:30 Bowel movements suppressed intensity setting and a cooler CCT. This produces footcandles of vertical illumination heavier in short (blue) wavelengths, which is more effective at producing a circadian response. In the evening, the lighted mirror can be adjusted to its lowest intensity and a warmer CCT. Though specific outcomes vary by individual, schedule, overall light exposure during the day, use of electronic devices before bed, and other factors, lighted mirrors are potentially supportive of circadian lighting strategies. ENERGY AND MAINTENANCE LED lighting, vacancy sensors, and dimmers all combine to minimize energy consumption and costs. LED energy efficiency is often evaluated based on efficacy. Analogous to miles per gallon metric for vehicle fuel efficiency, it expresses lumens of light output per watt of electrical input. Manufacturers may report efficacy for bare LEDs or the complete luminaire integrating the LEDs. Luminaire efficacy is generally lower than source efficacy, as the luminaire adds optical elements to distribute the light and control glare. Ask the manufacturer for efficacy for their products and whether it is based on source or luminaire. By adding dimming to the lighted mirror, additional energy is saved as the lighting element operates at a reduced level of power during dimming. Maintenance is another area where LEDs shine. Manufacturers typically rate lighted mirrors at 50,000 hours of source service life, at which point the lighting element will be visibly dimmer and may require replacement. If the driver is not high quality, it may fail before that point. For that reason, the driver should be serviceable; ask the manufacturer whether they intend to stock the required driver and for how long. Otherwise, throughout its life, a quality lighted mirror typically requires no maintenance, though periodic cleaning of the lens will maintain maximum light output. This may occur at the same time as cleaning Design Principles for Lighted Mirrors / 8

10 the mirror surface. ENERGY CODES In a commercial building, an energy code may regulate design building efficiency. LED vanity lighting offers lower wattage than traditional incandescent and more-efficient compact fluorescent lamps. A vacancy sensor generally completes code compliance. Some states also regulate residential lighting design. Residential building energy codes based on 2009 and later version of the International Energy Conservation Code (IECC) require that at least 50 to 75 percent of the lamps in permanently installed luminaires be high-efficacy. California s Title 24 energy code contains extensive requirements (see sidebar). Consult your local energy code for more information about specific requirements. Audio USB 9 / Design Principles for Lighted Mirrors

11 ROBERN TOPICS 1 ADDITIONAL OPTIONS Theoretically, a lighted mirror provides a platform for integrating a wide range of extended features. Two popular examples today include USB charging and audio. The audio option enables users to connect a smart phone to the mirror s speakers using Bluetooth and play music, podcasts, etc. These features offer very attractive amenities for users. CONCLUSIONS This paper recognizes lighted mirrors as a high-efficiency and highly aesthetic option for residential and high-end commercial bathrooms. It then identifies key points of evaluation to help ensure selection of an appropriate solution. Form factor, light output, glare control, color tone and rendering, controls, and additional optional features are all critical to evaluating, comparing, and selecting an appropriate lighted mirror solution. ABOUT THE AUTHOR GEORGE WAHLGREN is the Director of Product Development for Robern, Inc., A Kohler Company, headquartered in Bristol, Pennsylvania. Mr. Wahlgren leads Advanced Development, Industrial Design and Engineering, creating State of the Art Styling Spaces with cutting edge technology and precision design. He has also held the roles of Principal Engineer and Senior Product Development Engineer. Prior to these roles at Robern, he held roles at Stylex Seating, Inc., Metal Textile Corporation, AIL Research and National Tool & Manufacturing Co. Mr. Wahlgren earned his BS in Mechanical Engineering from Rutgers University. Design Principles for Lighted Mirrors / 10

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