FIELD OF THE INVENTION

The invention relates to the field of lighting arrangements. More precisely, the invention relates to a circadian lighting arrangement. BACKGROUND OF THE INVENTION

Light received by the eyes is one of the main influences on the circadian system which regulates physiological rhythms in the body, including hormone levels and the sleep-wake cycle. Light which influences the circadian system is referred to as "circadian light". The biological effects of light on humans can be measured in Equivalent Melanopic Lux (EML). A numerical ratio can be used to calculate the equivalent EML for light of a given type (with a given spectrum), so that the EML can be obtained by multiplying the measured visual lux with the numerical ratio. For example, the ratio for incandescent light is 0.54, while the ratio for daylight is 1.10.

The effects of such "circadian light" is governed by several factors. For example, circadian light is only effective when applied at a specific time, and light has to be applied during a certain amount of time depending on the intensity. The most effective circadian light is white and/or blue light that has an effect in melatonin suppression. Also, the angle with which light is projected towards the eye is very important.

The recently updated WELL Building Standard ® provides guidance for EML in various types of buildings. For work areas, the WELL standard stipulates that for 75% or more of workstations, at least 200 EML is present, measured on the vertical plane facing forward, 1.2 m [4 ft] above finished floor (to simulate the view of the occupant). This light level may incorporate daylight, and is present for at least the hours between 9:00 AM and 1 :00 PM for every day of the year.

US 2012/0259392 describes LED ceiling lights for emitting light influencing the state of the user. A light controller selectively controls the emission of the light including at least one of; the spectrum of the light; the duration of the light; the distribution of the light; the intensity of the light; and the timing of the light. An analysis engine capable of providing a signal to the light controller indicating a desired emission of the light based upon selectively illuminating one or more of a plurality of different blue light sources, each of which having a different peak spectrum.

A drawback of this solution is however that this lighting solution does not necessarily provide a lighting in different contexts for a subject that is similar to a natural illumination. For example, the color rendering of the skin and other objects under this light may not look natural.

WO2013153495A1 discloses a lighting apparatus comprising a first lighting device for providing task lighting on a horizontal surface and second lighting device for providing therapeutic light configured to illuminate an expected position of a face of a user.

US6021613A discloses an office screen with an integrated lighting feature especially at the crown of the office screen.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome this problem, and to provide improved circadian lighting, e.g. for workstations.

According to a first aspect of the invention, this and other objects are achieved by a lighting arrangement comprising a first lighting device for providing task lighting for illuminating a substantially horizontal surface, characterized in that the lighting arrangement further comprises a second lighting device for providing circadian lighting, wherein the second lighting device is integrated into a vertically extending office screen and wherein said second lighting device is configured to issue circadian lighting along a beam axis extending at an angle a with a normal to the office screen, with -15° <= a <= 30° for illuminating an expected position of a face (the eyes) of a user. Preferably 0° <= a <= 30°, for example a = 20°.

Task lighting is here to be understood as lighting for the purpose of enabling the carrying out of some kind of task mainly measured in the horizontal plane on the desk. By providing a lighting arrangement with circadian lighting that illuminates a user of for instance a workstation in a direction from the front will enable for the face of the user to be illuminated substantially vertically even when the person is sitting in an office and leaning slightly forward when reading, writing or working on his or her computer.

In the present applications, references to "horizontal" and "vertical" are made with respect to the direction of gravity. Vertical is thus a direction parallel to gravity, and horizontal is a direction normal to gravity. Similarly, "upper" should be understood as more distant in the vertical direction. The lighting arrangement may further comprise an office screen, wherein the second lighting device is integrated into the office screen. By having the second lighting device integrated into, or attached to the top of an office screen will enable for the lighting device to illuminate the face of the user in a desired direction.

The office screen may be connected to a desk with adjustable height, wherein the second lighting device is configured to illuminate the expected position of a face of a user in a horizontal direction at a predetermined height above the desk to establish a vertical illuminance level at the height of the face. By illuminating a predetermined height above the desk a solution with adjustable desk height can be used without having to adjust the height of the lighting arrangement, as the face of the user can be assumed to have a height over the desk that is substantially constant whether working while sitting or standing. Individual settings can also be used depending on the height of the user.

The second lighting device may be recessed into the top of an office screen, wherein the lighting arrangement further comprises a reflector above the office screen to distribute the light emitted from the second lighting device to one or both sides of the office screen depending if workers are working only on one side of the screen or on both sides in case of facing desks. An advantage of using reflectors is that the brightness of the reflective plane is, due to the size, relatively low, which will add to the visual comfort of the users.

The lighting arrangement may further comprise a detector for detecting a present user. The detector may be further configured to do an identification of the present user. The lighting arrangement may further comprise a control unit for activating the second lighting device based on data from the detector.

By controlling the lighting arrangement based on the presence of a user more efficient use of the lighting arrangement can be achieved. The identification of the user also enables for individual settings, such as light and EML exposure, to be used.

The control unit may be configured to limit the amount of circadian light that each user is subjected to during a day or other period of time. The lighting arrangement may then be set to turn off or lower the circadian lighting when a predetermined time of exposure is achieved for an individual or for a workstation.

The lighting arrangement may further comprise a user interface for communicating desired values of circadian light for a user. By using such an interface customized values of desired exposure times and/or intensities can be used depending on the individual and on recorded exposure from the past. The lighting arrangement may further comprise a sensor configured to detect the light emitted by the second lighting device and send information to the control unit. By using a sensor, the actual output of the lighting device can be logged and adjusted according to desired values.

The color temperature, or correlated color temperature (CCT) of the light emitted by the second lighting device may be between 3000 K and 6500 K. Lower color temperatures can also be used but in that case the ratios to calculate the EML are lower which will ask for higher illumination levels to be applied. By having a correlated color temperature of the circadian light between 3000 K and 6500 K the WELL standard can be easier met for EML illumination levels. Throughout the description the expression

"correlated color temperature" for devices is to be understood as to comprise both black body radiators, also referred to as Planckian radiators, having a specific color temperature, and to comprise nearly Planckian light sources having a correlated color temperature, i.e. the color temperature of the Planckian radiator that best approaches said nearly Planckian light sources.

The lighting arrangement may further comprise a third lighting device for providing ambient lighting generally upwards. Ambient lighting is here to be understood as general lighting or background lighting in the room. By providing ambient lighting in the same lighting arrangement the general feeling of the lighting in and around a workstation can be improved.

According to a second aspect of the invention, there is provided a lighting system comprising a number of lighting arrangements according to the first aspect of the invention, the lighting system further comprising a database for storing illumination (EML) data for a plurality of users and wherein the control unit of each lighting arrangement in the lighting system is configured to receive and send illumination data of the present user.

By connecting a plurality of lighting arrangements in a system for instance a whole workplace can be set up as a system wherein the lighting arrangements identify which user is at a workstation and accesses information about the user to provide a desired (EML) illumination profile and duration. It also ensures that no user is subjected to excessive amounts of circadian light and that optimization of illumination is enabled for users and workstations. As mentioned above, a user should typically be exposed for EML at least four daytime hours every day of the year, preferably in the morning, with at least two of these hours between 8-11 AM. The control units may be configured to adjust the intensity and/or correlated color temperature of the light emitted by the second lighting devices based on recorded amount of circadian light for the user.

The control units may be configured to adjust the intensity and/or correlated color temperature of the light emitted by the second lighting devices based on historical and/or expected user patterns of the user.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

Fig. 1 shows a lighting arrangement according to an embodiment of the present invention.

Fig. 2 shows a lighting arrangement according to a further embodiment of the present invention.

Fig. 3 shows a lighting arrangements according to a further embodiment of the present invention.

Fig. 4 shows lighting arrangements according to a further embodiment of the present invention.

Fig. 5 shows lighting arrangements according to an embodiment of the present invention, installed around the top edge of office screens around a workstation.

Fig. 6 shows a lighting arrangement according to another embodiment of the present invention, installed around the top edge of office screens around a workstation.

Fig. 7 shows a lighting system including a plurality of lighting arrangements according to an embodiment of the invention.

As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of

embodiments of the present invention. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

In the here illustrated example a special light giving desk divider is described which enables to make circadian lighting with the needed equivalent melanopic lux (EML) level with the desired spectrum in the vertical plane, preferably at around 1.2 m or (personal) vertical position of the eyes. By a vertical plane is meant that the light is sent in a

substantially horizontal direction. The circadian lighting can be adapted regarding the intensity of the light, and the time it is produced. Depending on the lighting device, also the correlated color temperature may be adapted. The expression "time" here refers both to the time of day and the duration of the EML illumination. For this a special user interface can be made which can be set manually or with help of an app, for instance on a PC or a

smartphone. At the same time, the light giving desk divider can, according to one

embodiment, add to the acoustic qualities in the space and the privacy feeling of the workers. By using illumination in the vertical screen it is also possible to improve the visual comfort for the worker. In this case the contrast between a (computer) screen and the surrounding back ground is reduced. It is also an option to provide a set circadian lighting in a building with EML levels which can be adapted over the time of the day. This will make it possible to ensure that people do not receive the wrong amount of circadian light. This can for example regulate that one does not receive too much blue light at the end of the working day. So when people take place at a desk with presence detection automatic the right circadian lighting is switched on.

The circadian light will have a given correlated color temperature (Tc). This Tc of the light can vary between for example 3000 K to 6500 K. When the color temperature is lower, the amount of light required to trigger the same body effects is higher (lower EML ratio). In general, the dose of EML is based on the duration of illumination, the intensity level of the illumination level and the color temperature or correlated color temperature (CCT). It may also be possible to use light with a specially designed spectrum helping to increase the EML.

In an embodiment according to the invention the light can be aimed into the eyes of the worker from a special light emitting desk divider or office screen. The height of the dividing screen might be adjustable so that people can adapt the height of the light emitting screen according to their personal body requirements. The EML light can be provided by directional light sources, which however may have the disadvantage that it results in disturbing glare, or with diffuse light radiating surfaces like opaque materials or back lighted textiles. Another option is to have an indirect lighting solution in which case the light is aimed to a reflective plane which reflects the light into the direction of the eyes of the worker. This has the advantage that the brightness of the reflective plane is, due to the size, relatively low which will add to the visual comfort of the users. This light should fall straight into the eye of the observer. Also an indirect light distribution version is described below.

Fig. 1 shows a lighting arrangement for a workstation according to an embodiment of the invention. Here two desks are divided by an office screen 9 in the form of a desk divider. Attached to a rod 6 on top of the office screen 9 is a first lighting device 1 for providing task lighting 2 to the office desk 3 on one side of the office screen 9. There is also provided a second lighting device 4 for providing circadian lighting 5, that is lighting with desired EML levels, to the user of the workstation on this side of the office screen 9. Even if the lighting devices are here attached to a rod 6 from the office screen, they can also be suspended in the roof above the office screen, attached directly to the office screen or integrated into the office screen. In figure 1 , only one lighting arrangement is illustrated (on the left side of the office screen 9) but another lighting arrangement may of course be arranged to illuminate the right side.

The second lighting device 4 here emits light at an angle around the horizontal plane, preferably at a height between 1 m and 1.4 m, e.g. 1.2 m, or a height corresponding to the eyes of a (sitting) person occupying the workstation. The EML levels may be provided per side individually so that each person can be measured independently and receive a personal EML level. The light may be made by lambertian light distribution surfaces like opaque or back- lighted textiles aimed at a height of 1.2 m or at the height of the face of the user. When textiles (or other soft translucent materials) are used in combination with the lighting arrangement it can also add to the acoustic quality of the space.

The lighting arrangement here also has a third lighting device 7 for providing further (indirect) ambient lighting 8. The circadian lighting 5, the ambient lighting 8 and the task lighting 1 here come from substantially the same position but illuminate different angles to illuminate mutually different areas in the office space.

The lighting arrangement here also comprise a fourth lighting device 10 for providing grazing lighting 11 for illuminating the office screen 9. The grazing light (ambi- light) here illuminates the office screen at a small angle from the surface of the office screen. The grazing lighting 11 provides a nice lighting detail to the workstation and also provides improvements to the general impression of ambient lighting. This ambi-light can also be realized with back lighting in the screen. By introducing RGB LEDs color effects can be made which can be linked to the computer screen (like applied with Philips ambi-light televisions) but also personal favorite color scenes can be set by the user offering to make the workplace more personal.

The lighting arrangement is here installed on a desk divider 9 between two office desks 3, however the invention is applicable to any workstations or positions occupied by a person. In other words, an individual desk can also be provided with a one sided lighting installation. Furthermore, the invention is not limited to dividers between workstations, but can also be used for instance in combination with a back plate of a desk against a wall.

The first, second and third lighting devices 1, 4, 7 may for instance be independent light emitting diodes (LEDs) installed next to each other. Alternatively, any combination of the first, second and third light emitting devices might use the same light source, wherein shading is used to create the circadian lighting, task lighting and/or ambient and ambi-lighting.

An indirect solution, i.e. where light from a light source is reflected by a surface into the desired direction, is illustrated in Fig. 2. Here, the second lighting device 41, e.g. in the form of a LED, is placed on the desk 3 with an indirect reflector 13 located above the LED. Each desk has a separate LED and reflector, to enable individual control. To avoid dis-comfort glare due to direct view the desk placed LED can be shielded of by means of a louvre or snoot. The reflector 13 itself here forms the office screen 9 and is covered with diffuse white material to avoid one to look into the light sources or a reflection of the light source in the screen, which would otherwise cause disturbing glare. On the left desk the reflected circadian lighting beam 5 has a beam axis 18 at an angle a, represented by ai, of 15 degrees with the vertical part of the office screen, on the right desk the beam axis 18 of the reflected circadian lighting is at an angle a, represented by a ₂ , of -6 degrees with the vertical part of the office screen.

Fig. 3 shows suspended indirect reflectors 131 where one single second lighting device 42 provides light for both desks, by means of one reflector 131 reflecting the EML light to both workplaces. The reflector 131 can for instance be suspended from the ceiling. A potential disadvantage here is that if one of the work places is not occupied the light is not used resulting in a less energy efficient solution.

Fig. 4 shows a system including two lighting arrangement similar to that in Fig. 1, and with individual control of the lighting arrangements. A sensor 14 is here arranged to detect a user occupying the desk and the second lighting unit 4 (light beam 5) can be turned ON and OFF based on input from the sensor 14. This also enables recording of illumination durations (in combination with the color temperature and the light intensity) at the workstation. In the time slot needed the circadian lighting can be provided. The lighting can be set with a special intensity and color temperature, for instance in given time intervals. As an example between 10.00-11.00 o'clock in the morning the screen circadian light will become active. Another option might be that a person activates the circadian lighting manually and makes himself known to a registration system. Another option could be here to activate the anti-jet leg therapy.

As will be discussed below, by further identifying the present user individual illumination data can also be accessed to make sure that the user is subjected to proper amount of illumination.

Fig. 5 shows how the lighting arrangement can be installed around the top edge of office screens 9 around a workstation. However the lighting arrangement could also be installed at single or multiple positions on or above the edges of an office screen 9.

Fig. 6 shows a solution with the lighting devices 1, 4, 7 installed as point sources on the corners office cubes. Also here there is a split between ambient lighting 8, circadian lighting 5 and task lighting 1. The advantage of this solution is that one receives light from two sides. For instance, when one of the office cubes is not occupied ¼ of the light distribution is switched off.

Fig. 7 schematically shows a system comprising a plurality of lighting arrangements according to an embodiment of the invention. In addition to a second lighting device 4, each arrangement includes a sensor 14 for detecting the presence of a user and identifying the user (see also figure 4) and possibly a light sensor 12 for measuring the light emitted by the second lighting device 4. A controller 15 is connected to receive information from the sensor 14 and light sensor 12, and connected to control the second light source 4. The system further includes a database 16 and central controller 17 connected to each controller 15.

The control unit 15 is configured to, when a user is detected, access information about recorded and desired illumination levels / color temperature combination for the specific user and to adjust the light emitted by the second lighting device 4

accordingly. As an alternative to the light sensor 12, emitted EML may be estimated by recording the duration during which the light source 4 is activated, together with information about the intensity and color settings during this time.

On possible way to identify the user is to use radio frequency (RF) tag recognition or identification in the sensor 14. Another option would be to use a camera with face recognition to find out the identity of the person sitting in front of the dividing screen and then get the personal data from the system. It can also be an option to use the camera of a PC screen or laptop for this function.

Personal identification will enable personal user settings related e.g. to the height of the person and age. The automatic the light emitting device can then be raised to fit the eye height of the observer or user. Personal identification also helps the system to log the illumination and to gather personal information about the EML levels received that day from a central data storage, as well as to access that information when deciding duration and intensity for the circadian lighting. This will also open the way to add extra personal information which could for example help to activate a therapy setting to reduce the effects of a jet leg after a (business) trip abroad.

The idea can furthermore work with a software program or an app to be installed on a PC or a smartphone which registers the time you are working at the desk. In addition to being useful in the context of the present invention, such information can also be used in a system which enables workers to find a free desk, or for directing cleaning services to a desk which has been used for a predetermined amount of time.

It is also an option to build in a light measuring sensor 12, as seen in Fig. 1, on the vertical plane of the desk divider. This will in combination with the color temperature measure how much EML is falling on 1.2 m height coming from the ambient and day light falling on the sensor. This light will be almost equal to the EML level falling on the face of the worker. The missing amount of circadian lighting can then be added to the existing measured available circadian lighting. This will enable energy savings due to EML day light harvesting.

From test the EML levels falling into the eye of the person sitting in front of the desk divider can be measured. As long as you stay active behind the desk the registration program will continuous update and count the EML doses a person is receiving during the specific hours, which comes from a combination of timing, intensity and color temperature, by sitting in front of the desk divider. By counting the time in combination with the color temperature and the intensity level of the illumination it is possible to measure if a person gets the minimum EML levels during the hours it should be provided.

For instance when people start relatively late with their EML light therapy the EML level can be increased. This can be done by increasing the color temperature, which results in a more bluish color, and/or the intensity of the emitted light. This so that one is able to receive the right EML dose in less than the 4 hours normally needed to receive the minimal EML level.

The simple registration system keeps track of which EML levels you have received that day. The system can calculate and then adapt the intensity levels of the illumination or the color temperature to make sure the worker gets the right minimal EML levels. When the minimum, or asked for, EML level is reached or the time in which this light should be given is over the system switches off the circadian desk divider light. In this way it is possible to give office workers the right EML level in the right time intervals. The desk divider can still radiate light but the intensity level and color temperature will be adjusted to the esthetical and/or visual needs. Even more saturated light color effects can be set then or the desk divider can be used for ambi-scene, linked to the settings to enhance your workplace experience.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, any combination of task lighting and ambient lighting can be used in combination with the circadian lighting.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Additionally the here described method can also be applied in other application segments like in hospitality environments, airports (for jet-leg therapy), workplaces in industry especially there where workers are working in shifts, educational centers, special environments like in sub marines etc.