Office task lights are used to illuminate localized tasks that take place at desks or workstations. Office work is visually demanding and has always challenged lighting to create visual conditions supportive of task performance, environmental and job satisfaction, social interactions, organizational productivity, and general health. Office lighting is often orchestrated in layers that work harmoniously to achieve an optimal luminous environment. Ambient and task layers of lighting, the two basic layers, are each fundamental to the functionality of an office space. A layer of ambient light creates a cohesive environment to make spaces appear more visually consistent and composed. A layer of task light creates visibility for specific areas where work needs to be performed. It provides focused, localized, and glare-free illumination with the right amount of illuminance and sufficient coverage of the task area. High quality task lighting lays the foundation for consistent concentration and productive work.
Office lighting is dynamic
Today’s offices are filled with dynamics. They are often designed with the flexibility to serve the changing layouts and diversified needs. In composing an office environment that contributes to long hours of uninterrupted concentration, efficiency and accuracy without fatigue, exclusivity must be injected into the lighting design in order to create private zones for undisturbed mindset and contemplation. Task lighting is intended to fill this need. It provides tailored lighting at each workplace to foster the critical individuality needed for creative, innovative and productive work to be delivered at a desk. While modern office lighting is generally orientated to horizontal visual tasks on desks, vertical lighting is also needed because computer-based tasks have become ubiquitous.
The dynamic nature of modern offices deems it necessary for task lighting to be flexibly adaptable to personal needs and the complexity of the task being performed. Addressing the requirements of such a diverse space is possible only with the use of positionable task lights which are located within convenient reach of the user. Overhead light fixtures are deficient in maneuverability, and consequently the flexibility to provide targeted illumination for relocated tasks. Also, ceiling-mounted task lights consume far more energy to illuminate a work area than localized task lights. Office lighting must comply with energy codes. A resource-efficient lighting solution therefore should prioritize the use of localized task lighting.
Office task lights
Office task lights designed for localized illumination include self-standing desk lamps, clamp-on desk lamps and floor-standing lights. Because they are located in proximity to the task plane, these lights are very effective in addressing the visual requirements of desktop tasks. Task lighting is an integral part of workspace ergonomics which attempts to reduce strain, discomfort, stresses, and fatigue by improving product design and workspace arrangements. Tilt adjustment of the light head is among the basic requirements of an ergonomically designed lights. The use of flexible gooseneck arms allows light heads to be twisted, turned and/or rotated effortlessly to desired directions. A task light of more sophisticated design uses a rotating light head and a fully adjustable, articulated arm structure, which provide an infinite number of positions and angles as well as extended reach for maximum light coverage. As an absolute minimum, localized task lighting should be provided with adjustability which ensures that the body does not need to compensate for poor lighting. Products of premium build quality come with a sturdy metal construction, which is needed to provide strength, stability and durability for dependable operation.
The enormous advantages of LED technology made it the logical choice for task lighting applications. An LED emits light through recombination of electrons and holes in its active region which is sandwiched between two oppositely doped layers of InGaN semiconductor material. This architecture allows to create white LEDs with a luminous efficacy far ahead of other types of light sources. The technology offers the new capability of precisely controlling the color characteristics of the light source by delivering a tailored spectrum that is achieved through phosphor conversion or additive color mixing. LEDs can be dimmed to produce a light output that is variable in full range. The ability to deliver the right amount of light on demand allows task lighting to be adapted to suit the needs of the user. The technology’s compatibility with semiconductor electronics (e.g., processors, wireless communication modules, sensors) has facilitated the implementation of sophisticated lighting control algorithms, which can be conveniently programmed or triggered with a smartphone app.
With LED technology, all essential characteristics of localized task lighting, including effectiveness, functionality and flexibility, are effortlessly delivered.
All LED system components must work in unison
In general, a holistic approach is taken in installing LEDs in a task luminaire. The performance and lifespan of LEDs are critically dependent on thermal management and drive current regulation. A high capacity thermal path must be constructed to dissipate thermal energy generated at the LED junction into the surrounding ambient air. Failure to effectively transfer heat away from the semiconductor devices may result in overheating the device package, which leads to accelerated lumen depreciation and eventually a shortened useful life. The drive current needs to be tightly regulated such that the LEDs are not electrically and thermally overstressed. The bulb-based configuration, which is used by traditional desk and floor lamps, failed to address the operational complexity of LEDs. Light bulbs create physical constraints to install a high capacity heat sink and a fully functional driver.
The holistic approach to system integration transforms the luminaire housing into a heat sink, which effectively increases the surface area of the thermal path. The LED module, which is typically an assembly of discrete SMD LEDs mounted on a metal core printed circuit board (MCPCB), is seamlessly affixed to the heat sink (in some cases via a thermal interface material). Heat generated by the LEDs is transferred to the heat sink via the shortest and largest possible thermal path. The critical junction temperature can therefore be kept low to maintain high efficacy and high color stability lighting over the product’s rated life.
Luminance and light distribution
The preference for an integrated LED system is also endorsed by the need to create a product with high photometric performance and visual comfort. In addition to illuminance level and color quality, effective visibility with task lighting depends on the control of luminance and uniformity. The output from LEDs is highly concentrated. Direct view of the LEDs, depending on their intensities, can lead to visual disability or discomfort. Exposure to high intensity cool white light for an extended duration may cause photochemical damage to the retina, which is referred to as blue light hazard (BLH).
Uniform distribution of illuminance across the task plane is equally important for visual comfort and task visibility. The human eye responds to luminance, which is the function of the surface illuminance and the reflective properties of the surface. It functions more efficiently when the luminances within over the task plane are fairly uniform. Luminance variations that are too great will create adaptation difficulties for the eye and the consequent eye fatigue and workplace dissatisfaction.
LED task lights either adopts a backlit or edge-lit optical architecture. In backlit systems, the LEDs project light through an opal diffuser or an optical lens that carries a diffusion mechanism. In edge-lit systems, the LEDs are arranged along the side of the luminaire. Light emitted by these LEDs is transmitted through a light guide panel (LGP) by means of total internal reflection (TIR). The LGP includes escape routes which direct the beams down towards an opal diffuser. The compound optical system creates a surface emission device that distributes light homogeneously with soft luminance.
The spectral power distribution (SPD) of the light source is designed with creating an atmosphere that has a positive impact on motivation, efficiency and productivity in mind. The spectrum is usually rich in short wavelengths of visible light. The emitted light appears cool white that exhibits a correlated color temperature (CCT) in the 4000 K to 5500 K range. Cool white light with a high percentage of bioactive blue light promotes the release of serotonin and cortisol while at the same time suppressing melatonin production, which causes the body to simulate a daytime physiological response for alertness, concentration, motivation and commitment. However, cool white light may be felt too harsh by some populations and in certain applications. Warmer sources such as those with a CCT around 3500K (which commonly referred to as having a “neutral white”) find their use when flattering light is desired.
Tunable white technology is trending. A tunable white task light is equipped with an LED module that integrates a number of controllable LED channels. Light output from LED channels is individually controlled to create a mixture of light, which provides the infinite variability to deliver a continuously adjustable range of color temperatures from warm white to daylight white. Dynamic tuning of the white light spectrum allows task lighting to be tailored to user needs and preferences.
Correct perception of the colors of objects is an important part of office task lighting. The wavelength distribution of the light generated by an LED determines how object colors are rendered. The SPD of light emitted by office task lights should be designed to achieve the required color rendering quality which is commonly characterized by the color rendering index (CRI). Products with a CRI of at least 85 should be employed for task lighting applications. When performing color sensitive tasks such as painting and art appraisal, a CRI of 90 and an R9 value of 50 are the minimums.
To deliver faithful color reproduction, the LEDs must deliver balanced amounts of radiant power across the visible spectrum. For phosphor-converted LEDs, the color rendering ability is a function of the semiconductor chips and the phosphor (wavelength conversion material) composition. Currently, the most frequently used white LEDs are blue-pump LEDs which utilizes a blue LED chip to pump phosphors within the device package. These LEDs are known for their high efficacy usually do not exhibit a balanced spectrum. Violet-pump LEDs which use violet-producing LEDs to pump red, green and blue phosphors are capable of distributing a sufficient amount of spectral content at every wavelength. They are used when the color rendering requirement is extremely demanding.
LED driving and dimming
An LED task light has an integral LED driver which regulates the power to the LED load. The constant current LED driver is required to supply a predetermined magnitude of DC power regardless of fluctuations in the supply voltage or LED forward voltage. The effects of flicker from light sources powered by an alternating current (AC) source have been a persistent problem. The various adverse effects of flicker include eye strain, distraction, blurred vision, fatigue, headache, migraine, as well as photosensitive epilepsy in sensitive individuals. An additional problem that is associated with flicker is that banding lines or “aliasing” show up during video conferencing.
The nearly instantaneous response of LEDs to changing current imposes special considerations on the flicker removal. Typically, the LED driver is designed as a switched mode power supply (SMPS) that delivers to its load a precisely regulated load with the current ripple value controlled within ±5%.
Task lights need to provide illumination that is highly controllable. To make lighting adaptive to task needs or to enable color mixing for tunable white lighting, the LED driver is required to allow dimming of the connected LEDs. An LED driver accomplishes this task usually through constant-current reduction (CCR) or pulse-width modulation (PWM).
OLED task lights
Task lights built on the OLED technology platform are capable of delivering high quality task lighting but come at a high price premium. The compelling benefits of OLED technology include high uniformity light distribution, soft luminance (naturally diffused light), high color rendition, ultra-thin profiles and the ability to be made in rigid or flexible forms. An OLED is a surface-emitting device composed of multiple organic layers sandwiched between an anode and a cathode. These organic layers are separately optimized for charge injection, charge transport and light emission. An OLED generates white light typically through additive color mixing of red, green and blue emitters. As with their inorganic cousins, OLEDs are also current driven devices that require tight drive current regulation.