EP2255125A1

EP2255125A1 - Led lighting device

Info

Publication number: EP2255125A1
Application number: EP08734631A
Authority: EP
Inventors: David Dussault
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2008-03-17
Filing date: 2008-03-17
Publication date: 2010-12-01
Also published as: US20110019433A1; WO2009115095A1; CN101978211A

Abstract

The invention relates to a LED lighting device equipped with multiple light emitting diodes, LEDs, which are fastened to a flexible substrate, wherein the flexible substrate is applied onto an arched surface of a carrier.

Description

description

LED lighting device

The invention relates to an LED lighting device with a plurality of mounted on a flexible substrate LEDs, LED, a set of several such LED lighting devices and a corresponding LED light.

It has hitherto been known to mount a flexible printed circuit board ('flexboard') equipped with LEDs flat on a support and then align the support in the desired direction of radiation. For this purpose, in particular equipped with LEDs flexible bands ('flex bands) are known, which are divisible and equipped with a self-adhesive back, z. B. the LINEARlight Flex series from. OSRAM, z. B. LMlOA with LEDs, which have a perpendicular to the mounting surface directed emission direction of the LEDs or LMIlA with LEDs, which have a parallel to the mounting surface directed direction of emission of the LEDs. Other LED-equipped flexbands include particularly high-performance LEDs (LM10P series from OSRAM) and flexbands with multicolor LEDs (series LM10L from OSRAM). However, this is constructively quickly consuming in lighting devices that are to radiate in a larger solid angle.

It is therefore the object of the present invention to provide a simple and inexpensive possibility for more homogeneous light emission in a larger solid angle, in particular in a circumferential solid angle of 360 °.

This object is achieved by means of an LED lighting device according to claim 1, a set of a plurality of LED lighting devices according to claim 20 and an LED lamp according to claim 23. Advantageous embodiments are in particular the dependent claims. The LED lighting device is equipped with several mounted on a flexible substrate LEDs, LED. The flexible substrate in turn is applied to a surface of a rod-shaped carrier.

As a result, it is possible to achieve a radiation of the LEDs of up to 360 ° revolving around a longitudinal axis by a simple and inexpensive design of the carrier, while the use of the flexible substrate results in a production-technically simple and inexpensive mounting solution of the LEDs on the substrate.

The flexible substrate may, for. B. as a flexboard or 'Flexfo lie' or 'Flexband' present, z. B. based on polyimide film substrates. In particular, the flex bands of the series LM-XX from OSRAM are suitable for this purpose. Typically, the substrate has electrical supply lines and optionally electrical components for the LEDs mounted thereon.

The carrier can then be present as at least partially straight or curved rod.

For spatially particularly homogeneous light emission of the carrier is preferably designed as a round rod-shaped carrier. Its cross section perpendicular to the longitudinal axis can then have, for example, a round or oval surface contour.

However, it may also be preferred for the particularly secure, especially flat mounting of the LEDs if the carrier is designed as a rod-shaped carrier, for example with a surface contour that is angular in cross-section perpendicular to the longitudinal axis, eg. B. quadrangular, hexagonal or octagonal. The LEDs then preferably lie on or over the flat segments of the carrier. For easy application and flexible arrangement of the light emitting diodes, an LED lighting device is preferred in which the flexible substrate is a belt-shaped substrate which is wound around the carrier.

For this purpose, it is particularly preferred if the LEDs are helically wound (helically) around the carrier, in particular with a constant pitch. In this case, the arrangement of the LEDs on the carrier can be controlled particularly easily, for. By adjusting the size and / or shape of the outer circumference of the carrier, the slope of the band on the carrier, and the LED density on the band.

For generating a homogeneous luminous flux, an LED lighting device is preferred, in which the LEDs are arranged in the longitudinal direction of the band at a uniform spacing.

For easy generation of a homogeneous luminous flux only in a subsector around the longitudinal axis around, z. B. in the range of 90 ° to 180 °, the LEDs in the longitudinal direction of the tape only in groups or sections are arranged at the same distance. Ie. in particular, that successive groups or sections of LEDs show the same LED arrangement pattern, but which does not have a uniform LED spacing. This allows the tape to be easily wound on the carrier and the LEDs concentrated in one or more angular sectors. For example, it may be advantageous for use in area lights.

For cooling the LED lighting device, it is preferred if the carrier is a tubular carrier. Then, the carrier which heats up due to the operation of the LEDs can cool down by means of a draft through the interior of the tube. The draft can be passive (chimney effect ¹ ) or active.

To increase the cooling power, an LED lighting device is preferred in which an inner wall of the tubular carrier At least one cooling rib is mounted, in particular a cooling rib extending in the direction of the draft (eg in the longitudinal direction). Preferably, a plurality of cooling fins are present.

To further increase the cooling capacity, an LED lighting device with active cooling is preferred. For this purpose, it is particularly preferred if the LED lighting device, a fan, for. B. a fan, for blowing air through the cavity or interior of the carrier.

For good heat dissipation and distribution, any good heat-conducting material can be used as support material, a material having a heat conductivity λ of more than 10 W / (mK), in particular more than 100 W, being under a good heat-conducting material / (mK), especially of more than 250 W / (mK). For example, stainless steel, low alloy steel, brass, etc. can be used. However, it is particularly preferred if the support comprises copper, aluminum or an alloy of copper, aluminum or both.

It is further preferred for ease of attachment when the substrate is secured to the carrier by means of an adhesive, in particular a double-sided adhesive tape or a liquid and then curing adhesive. Preferably, the curing adhesive cures due to heat development during operation.

It may be advantageous if a plurality of flexible substrates are arranged on a carrier. For example, several bands can be wound in parallel around a support, for. B. several bands, each with the same color, but between the bands differently colored LEDs. So z. B. three bands are used in the colors red, green and blue. But it can be accommodated per band and more LED strands with its own power supply line, z. In to the longitudinal direction of the tape parallel arrangement, z. B. three LED strands with in the colors red, green or blue.

In order to achieve a high light output, it may be preferred if the LEDs of a substrate comprise LEDs of the same color.

In order to make the LED lighting device shine in different colors, it may be preferred if the LEDs are color tunable. These can be provided externally or - preferably - arranged on the carrier drive electronics, z. B. comprises a sequencer.

Particularly preferred may be an LED lighting device in which the LEDs of a substrate comprise white LEDs, for. B. with a blue LED chip with downstream, from blue to yellow Wellenlängenumwandelndem phosphor, z. B. in surface mounting technology, z. In thin-GaN technology. Then an LED or an LED module can also have a plurality of white single chips, for. B. on a common submount, which can also achieve a simple scalability of the luminous flux.

It may be preferred if the LEDs of one or more substrates comprise differently colored LEDs. Then it is particularly preferred if the differently colored LEDs are combined to be emitted into white mixed light clusters, z. B. each as an LED module on a common submount.

Generally, instead of or in addition to inorganic light-emitting diodes, for. B. based on InGaN or AlInGaP, and organic LEDs (OLEDs) can be used.

The LEDs or LED groups (clusters) may be followed by suitable optics, for. B. a scattering lens or a wide radiating lens whose maximum light flux is not on its optical axis.

For large-area radiation and / or radiation with high light intensity, it may be preferred if a plurality of LED lighting devices are combined to form a set (a group).

For easy assembly and disassembly, the LED lighting devices are preferably detachably connected to each other.

It is particularly preferred if at least two LED lighting devices of the set are releasably connected to each other by means of a bayonet closure, wherein at least one flex band of one of the two LED lighting devices with at least one flex band of the other of the two LED lighting devices via an electrical connection unit, for. B. a plug, is electrically connected.

The LED lamp has at least one such LED lighting device or at least one set of a plurality of such composite LED lighting devices.

For further homogenization of the luminous flux, an LED luminaire is preferred in which the luminous devices are at least partially covered by a light-transmitting light scattering device, for. B. a diffuser (litter layer), z. B. a frosted glass, are surrounded or have such.

The LED luminaire can preferably be used as a decorative luminaire, as a signaling luminaire, in particular a hand-held signaling luminaire, or as a flat luminaire, for example. B. ceiling or wall sconce.

The LED light can also be accessible, especially for architectural applications. For this purpose, their inner diameter is configured correspondingly large. In the following figures, the invention will be described schematically by means of exemplary embodiments. The same or similar elements can be provided with the same reference numerals for better clarity.

1 shows a sketch in side view of an LED lighting device and a section thereof in an end region;

2 shows an oblique view of two LED lighting devices to be connected in the connection area;

FIG. 3 shows in a further oblique view the two now connected LED lighting devices from FIG. 2 in the connection area;

FIG. 4 shows, in yet another oblique view, the connected LED lighting devices from FIG. 3 in the connection region with an electrical connecting element;

5 shows a sectional view in oblique view a

LED lighting device with a fan;

6 shows a sketch in side view of a table lamp with an LED lighting device;

7 shows a sketch in side view of a decorative light with an LED lighting device;

8 shows a sketch in side view of a signaling light with an LED lighting device;

9 shows a sketch in an oblique view of a pedestrian tunnel; FIG. 10 shows an exploded view in oblique view of a surface light;

11 shows an exploded perspective view of a retrofit lamp with an LED lighting device.

1 shows an LED lighting device 1 with a round rod-shaped carrier 2, around the outer surface of which an LED flex belt 3 is wound in a helical manner. As shown in a cutaway shape in the right-hand circle, the flex belt 3 comprises a band-shaped flexible polyimide-based substrate 3a. At the side of the flexible strip 3 facing away from the carrier 2, light-emitting diodes (LEDs) 5 are arranged at regular intervals in the longitudinal direction of the strip. The flexible strip 3 or the substrate 3a also has here for the sake of clarity not shown - single or multiple - electrical lines and possibly electrical components for power supply and control of the LEDs mounted thereon.

The LEDs 5 are arranged so that their optical

Axis corresponds to the normal vector of lying below it outer O- surface of the support 2 substantially. The light-emitting diodes 5 are embodied here as white-light-emitting light-emitting diodes and can have one or more optics for shaping the luminous flux (not shown).

This LED lighting device 1 is easy to produce, results in a highly homogeneous light distribution about the longitudinal axis L of the carrier 2 and is easily adapted to desired requirements, eg. B. with respect to the light intensity, homogeneity of the luminous flux o- the radiation characteristic, adaptable. For example, the light intensity can be adjusted simply by the pitch of the helical line of the band-shaped substrate 3 and / or by the diameter of the carrier 2. Also, the light intensity can be increased by shortening distances between the LEDs 5. By means of suitable, not equal distances between the LEDs 5 can also be a targeted reach the inhomogeneous emission characteristic of the LED lighting device 1, as long as the distribution Wmkel about the longitudinal axis L. The flex band 3 is attached to the carrier 2 by means of an adhesive in the form of a self-hardening adhesive.

The power supply of the LEDs 5 can be done by means of a mains supply or a rechargeable battery, which are not shown here for better Ü bersichtlichkeit. A driver electronics for driving the LEDs 5 can be integrated on or in the carrier 2 or can be arranged externally, eg. In or on a power supply (not shown).

The electrical line is here designed multi-core, wherein the LEDs 5 are connected in parallel to each other between the individual supply lines or -wheels. As a result, open ends do not need to be treated further to carry the current. Especially with multi-colored LEDs (in particular LEDs with several individually controllable, differently colored LED chips) more than two wires can be used, for. B. one vein per color and a common Masseader. Alternatively, however, the LEDs or LEDs of the same color can also be connected in series, in which case a suitable electrical connection to the power supply must be ensured on an LED lighting device 1 serving as a single piece or end piece, eg. B. by connecting the open end of the strangled with the LEDs vein with a zuruckraufenden for power supply wire or by connecting the guttered with the LEDs vein with serving as a mass carrier.

In an alternative embodiment, differently colored LEDs can be used instead of the white LEDs 5. Among other things, it is possible to use color-tunable LEDs or a plurality of groups of LEDs in which the light-emitting diodes of different groups radiate in a different color. As a result, let the radiated by the LED lighting device color change. In this case, a sequencer (or other control device) may be used for the production of tion of these color effects by a suitable control of the LEDs externally or integrated on or in the carrier 2 be present. For example, it is generally possible to mount more than one flexible substrate on the carrier 2. For a color control of the LED lighting device, it may be useful, for example, to wrap at least three flexbands parallel to the carrier 2, each band having LEDs of a specific color ('LED string'), preferably in colors, which together result in a white mixed light can. Thus, three flex bands with red, green or blue LEDs can be wound in parallel on a support 2. A relative luminosity of the bands can then be adjusted very easily by a respective distance of the LEDs. If it is desired, for example, a lower luminous intensity of a certain type of light-emitting diodes, z. As the green LEDs, compensate by a higher number or density, the green LEDs of the corresponding flex band are set accordingly narrower. In general, use of the Flexband series LM XX from Osram is possible and preferred.

It is also possible, instead of an LED with a single chip, to use an LED which has a cluster with a plurality of individual chips, which are applied particularly advantageously on a common submount. These individual chips may have suitable colors, z. B. white or a combination of red, green and blue (possibly with an admixture of amber ("amber") to produce a warm-white white color) to give a white mixed light together, the common by a cluster downstream optics is decoupled. Of course, a single-chip LED can be provided with one or more optics. The optics are then preferably designed to obtain a homogeneous light distribution so that they "smear" or widen the luminous flux of the respective LED. For further homogenization of the luminous flux, it may also be suitable to use

To assign scattering element of each of the LEDs (for example, a scattering film), or it may be a scattering element, for. B. a frosted or milky translucent hood to the LED lighting device 1 and a part thereof are placed.

2 shows a possibility of a detachable connection between two LED lighting devices 1 according to FIG. 1 in the form of a bayonet closure, in order to achieve high design flexibility through a modular construction. For this purpose, each of the tubular supports 2 has a longitudinal slot 6 at one end in a basically known manner, at the end of which a short transverse slot 7 attaches at right angles. At its other end, the carrier also has a knob 8, which is also basically known, and which is inserted into the transverse slot 7 of the respective other carrier 2 to be connected. The arrows illustrate sketchy the required relative movement of the two carriers. The resulting set of LED light-emitting devices 1 can basically be extended as desired, taking into account possible limit values, for example a power consumption or mechanical strength limit values.

Alternatively, a simple plug-in closure can be used in which, similar to the bayonet closure, the outer diameter at one end of a tube corresponds to the inner diameter of the second tube, possibly with a locking device. It can, for. B. but also a screw cap can be used.

FIG. 3 shows the set of the two LED lighting devices 1

2, in which the respective carriers 2 have now been mechanically coupled to one another via the bayonet closure.

FIG. 4 shows the two connected LED lighting devices 1 from FIG. 3, wherein a plug 9 is provided for the electrical connection of the electrical leads of the respective substrates or flexbands 3. The plug 9 can be designed, for example, when using the LM XX-Flexbandreihe the Fa. OSRAM as a matching, so-called CONNECTSystem connector LM-XX Flex. A plug 9 can also be used as a feeder in the flex band 3, in addition to being a connector between two flex bands 3 (LM-CONN-IO Flex) (eg LM-2PIN with 2 connections for single-color LEDs or LM-4PIN with four Connectors for RGB LEDs with three different colored single LED chips) and then to the operating device (eg the power supply with driver electronics). Here, a tool-free installation is possible. For the electrical coupling of a flexbands or substrate but also other connection methods can be used, for. As a soldering or bonding with electrically conductive adhesive.

FIG. 5 shows a possibility of heat removal from an LED lighting apparatus 10. For this purpose, the lighting apparatus 10, as in FIG. 1 to FIG. 4, is provided with a tubular or tubular support 11, which hollow extends over the length of the support 11 Interior 12 has, which is open on both sides. During operation of the LED lighting device 10, the light emitting diodes (not shown) heat up and thereby also heat the carrier 11. The carrier 11 is for heat dissipation from the light emitting diodes and for good heat distribution of a highly conductive material, here: copper produced. The heating of the pipe 11 results in a chimney effect, in particular in the case of a vertical or substantially vertical position of the pipe 11, in which the air heated by the pipe 11 is removed upwards in the interior 12. In the embodiment shown, a fan 13 is placed to reinforce an air flow S through the interior 12 at the lower end of the carrier 11, which pushes cool ambient air into the interior 12 and thus achieves improved heat convection. The fan 13 is fastened here to a carrier 11 designed especially as an end piece, wherein the carrier terminates at its one, here lower end, with a foot 14. The foot 14 has corresponding fastening elements, here a screw hole 15 for receiving a screw 14 connected to the fan. However, the LED lighting device is not on one Such fan mounting limited, rather, the fan can be attached, for example, with a Baj onettverschluss analogous to Figures 2 to 4 on the carrier, and on the Baj onettverschluss other end pieces can be attached to a uniform carrier, for. As a foot or base or other elements, for. B. a handle.

FIG 6 shows a sketch of a standard lamp 16, in which an LED lighting device 1 is vertically mounted in a Lampenenso- disgust 17, z. B. by means of a bayonet lock, a plug closure or a screw cap. In the base 17, a power supply and a driver electronics for the LEDs 5 of the LED lighting device 1 can be accommodated. For homogenizing the light emitted by the LED lighting device 1, it is surrounded laterally and at the top by a dome-like translucent and diffusely scattering cover 18. The cover 18 may for example consist of frosted glass (opaque white glass) or frosted glass.

7 shows an LED lighting device 1, which is fixed vertically to a base 19, wherein the LED lighting device 1 is surrounded by a decorative element 20 in the form of a milky white translucent vase-shaped body. The power supply and control of this decorative light 21 is done via a combined supply device 22 with power supply and driver electronics.

FIG. 8 shows a portable signaling light 23, in which, similar to the light from FIG. 6, an upright LED lighting device 1 is covered by a milky-white, opaque cover hood 24. In a handle 25 is an accumulator (not shown) to power the LEDs 5 of the LED lighting device 1. By means of a switch 26, the signaling light 23 is switched on and off. Furthermore, the color emitted by the LEDs 5 can be set on the signaling light 23, either by a speaking operation of the switch 26 or another, not shown, switch. For example, the lamp 23 can be switched between a milky-green light emission and a milky-red light emission. Of course, the setting of other colors or mixed colors, eg. B. white, possible.

9 shows an embodiment of an LED device 27 in the field of architecture. The LED lighting device is in turn designed tube-shaped with an inner diameter which is large enough to allow walking on the LED lighting device 27. For this purpose, a catwalk 28 is guided by the LED lighting device 27. The flex band 3 with the diodes attached thereto (not shown) is now arranged helically on the inner wall of the LED lighting device 27. This creates a corresponding tunnel lighting. Of course, the flex band 3 need not be arranged helically.

10 shows a surface light 29 (wall or ceiling light) with a holder 30, a power supply 31 with integrated LED driver electronics, two end contacts 32, a cover plate 33, an LED lighting device 34 and a cover 35. The LED lighting device 34 has not shown terminal contacts in electrical connection with the electrical lead of the LED lighting device. In this sense, the LED lighting device 34 can also be viewed as a festoon lamp. The LEDs 5 emit white (cold white or warm white) light. In the illustrated embodiment, the LEDs 5 are arranged substantially uniformly about the longitudinal axis of the LED lighting device 34; light emitted to the sheet 33 can be emitted outside, for example, by reflection through the milky-white cover 35. However, it is also possible to enforce the distances of the LEDs 5 so that they are arranged substantially laterally and downwardly, but not upwardly in the direction of the sheet 33. This results Alternatively, however, the LED lighting device can also have contacts only on one side, in which case there are preferably several connections.

FIG. 11 shows an LED fluorescent tube retrofit lamp 36 with the LED lighting device 1. In this case, the LED lighting device 1 is surrounded by a light-diffusing translucent diffuser tube or diffuser hood 37. As a result, the Lichtab- radiation is further homogenized. The electrical contacts 38 are provided only at one of the two ends, for. B. with two terminals for single-chip LEDs) or z. For example, four ports for RGB multiple LEDs. For installation in a conventional fluorescent tube housing the lamp 36 is equipped with an integrated therein, not shown here operating device.

Of course, the present invention is not limited to the embodiments shown. Thus, instead of a helical winding a plurality of flex strips can be used in an arrangement in which they are arranged in a straight line in the longitudinal direction of the carrier and parallel to each other; However, this is not preferred due to the increased connection costs.

LIST OF REFERENCE NUMBERS

1 LED lighting device

2 straps 3 Flexband

4 substrate

5 LED

6 longitudinal slot

7 transverse slot 8 button

9 plugs

10 LED lighting device

11 carriers

12 interior 13 fans

14 sockets

15 screw hole

16 floor lamp

17 Lamp base 18 Cover

19 sockets

20 decorative element

21 decorative light

22 Supply device 23 Signaling light

24 cover

25 handle

26 switches

27 LED device 28 Catwalk 28

29 ceiling light

30 bracket

31 power supply

32 end contact 33 sheet

34 LED lighting device

35 cover 36 LED lamp

37 Diffuser hood

38 electrical contact

39 wire

L longitudinal axis S airflow

Claims

claims

An LED lighting device (1; 10; 27; 34) having a plurality of LEDs (5) mounted on a flexible substrate (4), the flexible substrate (4) being mounted on a surface of a rod-shaped carrier (2).

2. LED lighting device (1; 10; 27; 34) according to claim 1, wherein the carrier is a round rod-shaped carrier (2) or kantstabförmiger carrier.

The LED lighting device (1; 10; 27; 34) according to claim 1 or 2, wherein the flexible substrate (4) is a belt-shaped substrate wound around the carrier (2).

An LED lighting device (1; 10; 27; 34) according to claim 3, wherein the LEDs (5) are helically wound around the constant pitch support (2)

5. LED lighting device (1; 10; 27; 34) according to claim 3 or 4, wherein the LEDs (5) in the longitudinal direction of the band-shaped substrate (4) are arranged at a uniform spacing.

6. LED lighting device according to claim 4 or 5, wherein the LEDs (5) are arranged in the longitudinal direction of the band-shaped substrate (4) in only a group of the same distance.

7. LED lighting device (1; 10; 27; 34) according to one of the preceding claims, in which the carrier (2) is a tubular carrier (2).

8. LED lighting device according to claim 7, wherein at least one cooling fin is attached to an inner wall of the tubular support (2).

9. LED lighting device (10) according to claim 7 or 8, further comprising a blower (13) for blowing air (S) through the cavity (12) of the carrier.

An LED lighting device (1; 10; 27; 34) as claimed in any one of the preceding claims, wherein the substrate (4) is fixed to the support (2) by means of a double sided adhesive tape or a hardening adhesive.

11. LED lighting device (1; 10; 27; 34) according to one of the preceding claims, in which the carrier (2) comprises a highly conductive base material.

The LED lighting device (1; 10; 27; 34) according to claim 11, wherein the support (2) is made of copper and / or aluminum or an alloy thereof.

13. LED lighting device according to one of the preceding claims, wherein a plurality of flexible substrates on a support (2) are arranged.

14. An LED lighting device (1; 10; 27; 34) according to one of the preceding claims, wherein the LEDs of a substrate

(4) include same color LEDs (5).

15. LED lighting device according to claim 14, wherein the LEDs of a substrate (4) are tunable in color.

16. LED lighting device (1; 10; 27; 34) according to one of the claims 14 or 15, in which the LEDs of a substrate (4) comprise white LEDs (5).

17. LED lighting device according to one of claims 1 to 13, wherein the LEDs of a substrate (4) comprise different colored LEDs.

18. LED lighting device according to claim 17, wherein the different colored LEDs are combined to be emitted into white mixed light clusters.

19. LED lighting device according to one of the preceding claims, wherein on the carrier (2) a driver electronics for the LEDs is mounted.

20. Set of a plurality of composite LED lighting devices (1; 10) according to one of the preceding claims.

A kit according to claim 20, wherein the LED lighting devices (1; 10) are detachably connected together.

22. The kit as claimed in claim 21, wherein two LED lighting devices (1; 10) are detachably connected to one another by means of a bayonet closure or plug-in closure, at least the LEDs (5) of a substrate (2) of one of the two LED lighting devices (1; ) are electrically connected to at least the LEDs (5) of a substrate (2) of the other of the two LED lighting devices (1; 10) via an electrical connection unit (9).

23. LED lamp (16; 21; 23; 29; 26) with at least one LED lighting device (1; 34) according to one of claims 1 to 19 or a set of a plurality of composite LED lighting devices (1; Claims 20 to 22.

24. LED light according to claim 23, wherein the Leuchtvorrich- tions at least partially of a translucent

Light scattering device (18; 20; 24; 35; 37) are surrounded.

25. LED light according to claim 23 or 24, which is designed as a decorative light (16; 21).

26. LED luminaire according to claim 23 or 24, which is designed as a signaling light (23), in particular a hand-signaling light.

27. LED light according to claim one of claims 23 to 25, which is designed as a surface light (29).

28. LED light (27) according to claim 23 or 24, which is accessible.