BACKGROUND OF THE DEVICE — field of technology

This device relates to the field of LED substitution light sources for indoor ambient illumination. The new high-brightness LED light sources are rapidly replacing all prior illumination technology for indoor ambient light. The new LED technology must adhere to the existing infra-structure which, in USA, supports the filament A-series with Edison screw light bulbs , the long, tubular fluorescent lights then also the larger high-pressure gas lamps mercury vapor , metal halide G12 socket , metal halide sports floodlight , sodium lamp and others . The first technology (light bulbs) is the queen of home illumination systems, the second, the long tubular fluorescent, dominates the commercial and educational buildings, while the third group, the high pressure gas lamps, is used mostly for large industrial spaces and outdoor illumination. In Europe there is a substantial use of low-voltage halogen home illumination too. We do not know the existing situation on the rest of the world besides USA and Europe, but expect that the countries that are now or have been in the past dominated by USA follow the same pattern as USA.

The new-technology LED must fit into the existing standards, which is relatively easy to do, including the physical support and the decrease in the electric potential to power the LEDs and the current limiting circuits, both of which can be made with integrated circuit technology then integrated into the devices. Accordingly, several LED-based light sources are in the stores that are plug-compatible with the existing technologies and standards associated with them, as the incandescent lamp substitutes Incandescent-like1 , and Incandescent-like2 , or the fluorescent lamp substitutes with clear glass envelope , and with frost glass envelope . Perhaps because of the speed of introduction of these LED-substitutes there has not yet been time for the people involved in their design to be creative with the adaptation, making the substitutes not only physically and electrically compatible with the existing hardware (say, the Edison-screw for incandescent bulbs) and with the electric standard (120 V in US, 220V in Europe), but, on top of this, modifying what is necessary to take advantage of any possible difference between the LED technology and the older ones . One of the differences is that the LED is fairly forward emitting, while both the incandescent bulb and the fluorescent tubes are quite isotropic, emitting almost the same light intensity along all directions. We are here proposing some modification on the new LED-based devices that take advantage of some of these differences to improve the result, as energy saving, or more light output, or etc.

It seems that the speed of introduction of LEDs caused that no thought has been devoted to the adaptation of the type of light produced by the LEDs to the pre-existing technology, limiting itself to adapting the physical support and the electrical characteristics of the adaptation. This adaptation is the objective of our devices.

BACKGROUND — Discussion of Prior technology

Prior to the current introduction of LEDs for illumination the field has been dominated by three technologies, namely, the home-style light bulbs (figures 1a, 1b and 1c), then the mostly commercial and school use long tubular fluorescent lamps (figure 1d), and finally the larger high-pressure vapour lamps (figure 1e), as shown below


            Figure 1a                             Figure 1b                                 Figure 1c                             Figure 1d                             Figure 1e
      incandescent bulb               incandescent bulb                   incandescent bulb                   fluorescent light         high-pressure metal halide
          visible filament                   visible filament                       frosted glass                           frosted glass                                                

                                                                            Click on any picture for an enlarged view of it

We will concentrate here on the two first types of illumination devices, the incandescent light bulbs and the fluorescent lights, leaving the high-pressure lamps for later. Both the incandescent bulbs and the fluorescent lights emit light on a 4 * pi stereoradians (that is, isotropically, the light is emitted almost the same intensity on all spacial directions). Some devices include a light collector and colimator, as a searchlight or a headlight, but still the initial light emission is isotropic, and most cases of their use are for space illumination, and the objective is an evenly distributed light on all the room. The incandescent light bulb has a problem with this, because the light is emitted from a small filament (see figures 1a and 1b), which is then too bright to be looked at. As a first step to correct for this high brightness, the glass bulb of most incandescent lamps is a frosted glass (see figure 1c), which scatters the light, causing that the light is spread, emanating from the full surface area of the glass enclosure, and not so concentrated from a small filament, being therefore not so much offensive. Moreover, light originating from a small area causes pronounced shades, which is to be avoided for a better psychological, peaceful environment. For the fluorescent light, they all must have a " milky " appearance because the actual gas inside emits much ultraviolet photons, which then must be converted into visible photons (also to get rid of them because they may cause harm to the eye and skin). For this purpose, to down-convert the ultraviolet photons, a phosphorous coating is spread in the inner side of the tube, which is capable of down-converting the photons to several wavalengths, the combined effect producing the known while light which then originates from all the inner surface of the tube, a fairly large area, with the consequence that the fluorescent lamps have a relatively small intrinsic brightness (light energy per unit of area).

Between these two technologies, the incandescent light bulb and the fluorescent light, the fluorescent offers two advantages. Firstly the fluorescent light illuminates from a low enough brightness per unit area that if a person's eyesight passes through the actual lamp the brightness is perfectly tolerable, not bright enough to cause any discomfort on the viewer. Secondly, the fluorescent light being so much larger than the incandescent bulb there is a large enough area emitting light that it produces little shadow, if any shadow at all. It is important to highlight these points here because our proposed improvements for the LEDs is with a similar objective.

As a consequence of the larger intrinsic brightness of the incandescent light bulb, due to the geometry and sizes, even the frosted light bulb , which reemits the same light coming from the tungsten filament but from a larger surface area, is still too bright per unit of light emitting area, so in most cases the incandescent light bulb is inside a second scattering surface, which may be a paper or cloth enclosure (figure 2a) , as for floor lamps in rooms, or glass scttering shades if on the ceiling , or something else. Note here that the floor shades are generally open at their top and bottom, which happens exactly because there is little chance that a person will look directly from either of these directions, so there is no need to protect the eyes of a person, while a diffusive surface there would unnecessarily decrease the intensity of light escaping along these directions, so they are left open, though there is another reason too, which is to facilitate air flow around the light bulb for bulb temperature control. Some fluorescent lamps are also behind some second scattering surface to further spread the light as in figure 2c , or in figure 2d , but because their intrinsic brightness is less than the intrinsic brightness of the light bulbs, this second scatterer is less common in front of fluorescent lights then with the incandescent light bulb.


                                                    Figure 2a                                     Figure 2b                                 Figure 2c                             Figure 2d
                              Some lamp shades for floor lamps           lamp shades for ceiling lamps       flourescent lamp shade         fluorescent lamp                                                                                                                                                                                                                     shade


It is an objective of the device to cause a more evenly spread illumination in the space. It is another object of the device to take advantage of the directionality of the light emitted by the LEDs to allow the elimination of scattering surfaces surrounding the new LED luminaries, because these scattering surfaces also absorb light, and light absorption decreases the overall efficiency of the LEDs as light sources.


This paper discloses several method and means to cause a more isotropic illumination (evenly spread along all directions) originating from LED light sources. A secondary advantage of the method and means is to obviate the need of shades, as here , or here . Shades are used to scatter the light, both to cause that all points in the room receive light from more directions, therefore preventing shadows, but also to prevent too bright a light to reach the eyes of persons in the room. The method and means proposed also increase the efficiency of the device, when compared with existing ones, because it obviates the necessity of scattering shades which also absorbs light, which in turn decreases the illumination efficiency. This is easily seen to be the case when one consider that materials that scatter more, generally also absorb more, so the high scattering shades also absorb quite a lot of the light.


As explained above, the reason for the shades around the light sources is to scatter the light inside it, both to increase the surface from which light propagate into the room in order to decrease shadows (the surface of the shade is larger than the surface of the light source in all cases) and also to prevent a too bright a light source to be seen directly by any person in the surrounding space. Shades would be unnecessary if the light source were already dim per unit of surface area. An example of a relatively dim light source, while of a relatively large surface area, is the fluorescent light, which, accordingly, often is not encased in a scattering surface. We further believe that the cases in which the fluorescent lights are encased in a frosted glass/plastic happen for fashion and not to meet human needs.

Incandescent light bulbs are, in general, a little on the too bright side for direct view, so they are accordingly often encased in a shade, besides being generally of the frosted glass type bulb too.

DETAILED DESCRIPTION — function of the shades and how to avoid them

Shades exist for the dual purpose of firstly increasing the surface area from which light originates (this decreases shadows) and secondly to prevent a too bright a light source to interfere with the vision of people in the room (they are annoying if the eye passes by them). If the shades have eventual decorative function, these are introduced only to increase their appeal, but it is unlikely that the decorative function of the shades was the initial reason for their introduction. There is no reason for the shades to completely cover the light source, but only along such directions as a human may look, and accordingly the shades encasing light bulbs at the eye level only protect along such directions, being open at the top and bottom ( see figure 2a ).

LEDs are by nature very directional light emitters, perhaps the most directional of the existing light sources used for space illumination (lasers are more directional than LEDs but they are not used for space illumination). It follows from this directionality characteristic that if the LEDs were be positioned in such a way as to emit light along such paths that do not intercept human eyes in any of the likely positions the people in the room may be, then the second of the reasons stated above for the shades (to prevent bright beams to hit human eyes) would no longer exist. An example of such a case is shown in figures 3a and 3b, in which the light from a 12W LED source located on top of the bookshelf, just below the ceiling, points to the higher part of a nearby wall. Given the particular location of the furniture, humans are not likely to cross that light beam. Note that the light spot in 3b is not actually brighter than in 3a (it is the same spot within seconds of each other), but it appears to be brighter because the pictures were taken with an automatic camera that averages the illumination, so the darker area at the left of figure 3b causes a longer exposure time and the brighter area becomes super-bright in the picture.

The second reason for a shade is to provide a larger area to be source of the room illumination (to avoid shadows), and a substitute for a shade should perform a similar function. The high LED beam shown in figure 3a and 3b provides such a large bright area, which is the wide spot created on the wall by the LED beam emanating from the top of the bookshelf. In fact, the illuminated area is much larger than the surface area of any lamp shade I have ever seen. It is our contention then that the arrangement shown in figure 3a and 3b provides a good room illumination without the shades that absorb light and therefore contribute for a decrease in the available light, which is not desirable. The LEDs shown in figure 3a and 3b are pointed to diffuse reflective surfaces, the ceiling and high places on the wall, then these diffuse reflective surfaces appear as relatively bright spots but not excessively so, which in turn, scatter the light to all directions in the room, and this light, after the first hemispherical reflection (2 * pi stereoradians) is low enough brightness, when viewed from any direction, as to not disturb anyone in the room at any time. Since the conditions of preventing a too bright beam to impinge on a person's eye and of illuminating the room from a large area to prevent shadows are satisfied, it follows that the shades are not necessary, and with them the loss of illumination caused by their light absorption. Of course that it would still be possible for a person to position himself on purpose in front of the LED beam directed at the higher portions of the wall and then get himself bothered by the bright light, as seen in figure 3c, but the objective here is to prevent this to happen unwilingly, not to happen on purpose.


              Figure 3a                           Figure 3b                       Figure 3c
          Light from LED                 Light on wall           direct view of LED        
              on wall                 also scatters from ceiling     from near wall spot                                                                          
                                                                                        Looking into LED
                                                                                      from just below print

DETAILED DESCRIPTION — proposed LED arrangements for Edison-screw light bulbs

We now propose 2 1/2 types of LEDs to use for home illumination using the Edison screw technology used by the incandescent bulbs (three types, one of which being but a small variation of other, so we count it as a 1/2). Edison screw bulbs are used in one of two main positionings, namely pointing up or pointing down. There exists a small number of cases where the bulb points horizontally, which we leave out here for simplicity but we have proposed solutions for these cases too. Where the fixture is of such a type that the incandescent bulb points up, as in any of the types of the floor lamps shown in figure 2a, we propose 1 1/2 types of LED substitutes which we tentatively call here direct-type and convex-type as shown in figures 4a   4b   and 4c . In each of these options the objective of the design is (1) to keep the direct light from the eyes of people around and (2) to direct the emitted light to diffuse scattering surfaces preferably with a large area. Note that these LED substitutes for the old incandescent bulbs are designed to substitute incandescents that are used in floor or furniture standing luminaries, as in figure 2a. This design precludes direct light into the eyes of people in this case.

Proposed LED configurations physically compatible and intended to be substitutes of Edison-screw incandescent bulbs

For luminaries that hang from the ceiling pointing up, as in figure 5a , figure 5b , figure 5c our preferred LED substitution for the incandescents are 4a   and 4b , while for luminaries that hang from the ceiling pointing down as in figure 5d , out preferred LED substitution for the incandescents is 4d , projecting the light backwards, of course, to avoid the uneasy brightness shown in figure 5d .

                        Figure 4a                                               Figure 4b                                               Figure 4c                                             Figure 4d
                  Flat shape                                               Concave shape                                         Flat shape                                     concave shape
          forward emitting LEDs                               forward emitting LEDs                       forward and backward                     backward emitting LEDs                                                

Luminaries at ceiling, pointing up (5a, 5b and 5c) and pointing down (5d)


                Figure 5a                                 Figure 5b                                   Figure 5c                                       Figure 5d
    LED at ceiling pointing up       LED at ceiling pointing up         LED at ceiling pointing up                 Incandescent bulb
      forward emitting LEDs             forward emitting LEDs             forward emitting LEDs                 at ceiling pointing down
                                                                                                                glass shade out

CASE STUDIES — proposed LED type use




DETAILED DESCRIPTION — proposed LED arrangements for tube-type fluorescent lamps

1. current LED substitutes for fluorescent tubes.

Likewise for the incandescent bulbs, existing substitutes for the tube fluorescent lamps just stick some LEDs in a mechanically compatible support with little consideration of the different intrinsic characteristics of the two technologies. For example figure 6a is an LED in a tube-type fluorescent , and so is figure 6b . When energized from the ceiling such lamps produce several very bright light beams propagating within a few degrees around the vertical down from the ceiling. The bright beam is likely to disturb humans in the space. Accordingly, the LED substitutes for the fluorescent tubular lamps are made with both a clear glass enclosure as in figure 6c , and a frosted glass enclosure as in figure 6d , this latter being preferable.

LED substitutes for tubular fluorescents


                Figure 6a                                           Figure 6b                                           Figure 6c                               Figure 6d
    ← - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LED sources mounted in a - - - - - - - - - - - - - - - - - - - - - - - - - - - - - →
    ← - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - tubular fluorescent -type support - - - - - - - - - - - - - - - - - - - - - - - - - - - - →
    ← - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - clear glass - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - →             frosted glass                                                    

Most of the tube-type fluorescent lamps are used either inbeded into the ceiling as in figure 7a or else hanging from the ceiling as in figure 7b or figure 7c . Accordingly we will propose here one type arrangement with LEDs that is capable of providing a good distributed light from the ceiling and using the existing fluorescent light fixtures. Note, however, that we propose some modifications on the locations of the LEDs on the hardware, in order to take advantage of the directionality of the light emitted by the LEDs. Our example is for the case of embeded fluorescent lights, as in 7a, but it is an easy adaptation for hanging fluorescents as in 7b or 7c.

Figure 7d shows two simplified redentions of one of our proposals for the LED substitution for the fluorescent lights. One of the principles determining our choices is that LED luminaries located in positions higher than people, should not emit light downwards, to avoid annoying bright lights in people's eyes; LED lights originating from higher than 1,80 m (6 feet) should emit vertically and all the way down to a little below the horizontal, from where the light is scattered by the ceiling and by the walls to the rest of the room. For the LEDs substituting the imbeded fluorescents we recommend a dropped LED support, as shown in figure 7d, which consists of a rigid support that has the dimensions of any of the old fluorescent (they come in several lengths and our devices would do so accordingly), this rigid support being also capable of making the necessary electrical connections at its end then carrying the electrical connections down the support cable which runs through a small hole on the false ceiling, to the actual support for the LED at the bottom of the upper part of figure 7d. On this LED support there are a number of LEDs as shown in the bottom part of figure 7d, which is a view of the support from its extremity, looking into the length of it. LEDs exist at the top and sides of the support, with a few LEDs pointing a few degrees below the horizontal, probably no more than 10 dgs. below the horizontal, the actual value depending on the room size, with view of preventing direct LED light into people's eyes. The false ceiling used by our device should never be a frosted glass/plastic, because in the case of our device the light is below the ceiling, so the best is to have a light color (highly reflective) diffuse reflector, capable of spreading the impinging light on all directions in the room.

If, on the other hand, for reasons of fashion it is chosen to have the LED substitution for the fluorescents still embeded into the dropped ceiling, then the LED substitute should be as shown in figure 7e, with LEDs spanning 150 degrees (15 degrees below the horizontal on each side) and pointing downwards, with the prior technology of the frosty glass/plastic as in figure 7a. For this case we add another modification, which is impossible to implement on the fluorescent, which is diverging lenses in front of each LED, which serves the purposes of increasing the light spot on the inner part of the frosty glass/plastic, with concomitant increasing on the area of the surface which spreads the light to the room, causing less bright spots on the frost glass/plastic. This positioning for the LEDs differs from the positioning on the existing LED supporting device as shown in figure 6a and 6b, for example, in that the LEDs as shown in figures 6a and 6b cause a concentration of light spots on the scattering surface (say, the frosted glass/plastic), which in turn become unecessarily too bright.


            Figure 7a                             Figure 7b                           Figure 7c                           Figure 7d                           Figure 7e

    ← - - - - - - - - - - - - - - - - - - - - - Fluorescent light - - - - - - - - - - - - - - - - - - - - - →       ← - - - - Proposed LED placement - - - - - - - - →
  ← - - - - - - - - - - - - - - - all covered with frosted plastic - - - - - - - - - - - - - - - - →         ← - - - - on fluorescent -type support - - - - - - - →
  imbeded into ceiling       ← - - - - - - - - - - hanging from ceiling - - - - - - - - - - →           pointing upwards       pointing downards
                                                                                                                                      on hanging lamps       on imbeded lamps                                                    


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