Side emitting LED and lens

Details Side emitting LED and lens Side emitting LED and lens

2002-06-24

2004-01-20

Cariaso, Alan (Department: 2875)

Illumination

Light modifier

Refractor

C362S308000, C362S337000

Reexamination Certificate

active

06679621

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to light emitting devices and more particularly to side emitting light emitting diodes (LEDs).
BACKGROUND
FIG. 1A
illustrates a conventional LED package
10
. LED package
10
has a hemispherical lens
12
of a type well-known in the art. Package
10
may also have a reflector cup (not shown), in which an LED chip (not shown) resides, that reflects light emitted from the bottom and sides of the LED chip toward the observer. In other packages, other types of reflectors reflect the LED chip's emitted light in a particular direction.
Lens
12
creates a field of illumination
14
roughly along a longitudinal package axis
16
of LED package
10
. The vast majority of light emitted from an LED package
10
with a hemispherical lens
12
is emitted upwards away from LED package
10
with only a small portion emitted out from the sides of LED package
10
.
FIG. 1B
illustrates a known light emitting diode (LED) package
30
with a longitudinal package axis
26
. LED package
30
includes an LED chip
38
, a lens
32
with straight vertical sidewall
35
and a funnel-shaped top surface
37
. There are two main paths in which the light will travel through package
30
. The first light path P
1
is desirable with the light emitted from chip
38
and traveling to surface
37
where total internal reflection (TIR) causes the light to exit through sidewall
35
at approximately 90 degrees to the longitudinal axis. The second light path P
2
is light emitted from chip
38
towards sidewall
35
at an angle causing TIR or a reflection from sidewall
35
causing the light to exit package
30
at an angle not close to perpendicular to the longitudinal axis. This path is not desirable and limits the efficiency of side extracted light.
FIG. 2
illustrates the conventional LED package
10
of
FIG. 1
coupled along an edge of a portion of a refractive light guide
20
. LED package
10
is positioned on the edge of light guide
20
along the width of light guide
20
. Light rays R
1
, R
2
, R
3
emitted by LED package
10
are propagated along the length of light guide
20
.
FIG. 3
illustrates a plurality of conventional LED packages
10
positioned along the width of light guide
20
of FIG.
2
. These conventional LED/light guide combinations are inefficient as they require a large number of LED packages
10
to illuminate the light guide and result in coupling inefficiencies due to relatively small acceptance angles. These conventional LED packages
10
must be arranged along the entire length of one side of light guide
20
to fully illuminate light guide
20
.
A need exists for an LED package to couple efficiently to shallow reflectors and thin light guides. A need also exists for an LED package to allow these secondary optical elements to have relatively large illuminated areas.
SUMMARY
In accordance with one embodiment, a lens comprises a bottom surface, a reflecting surface, a first refracting surface obliquely angled with respect to a central axis of the lens, and a second refracting surface extending as a smooth curve from the bottom surface to the first refracting surface. Light entering the lens through the bottom surface and directly incident on the reflecting surface is reflected from the reflecting surface to the first refracting surface and refracted by the first refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens. Light entering the lens through the bottom surface and directly incident on the second refracting surface is refracted by the second refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens.
The inventive lens may be advantageously employed to provide side-emitting light-emitting devices that may be used with light guides and reflectors that have very thin profiles and/or large illuminated areas.
In accordance with another embodiment, a light-emitting device comprises a light-emitting semiconductor device and a lens. The lens comprises a bottom surface, a reflecting surface, a first refracting surface obliquely angled with respect to a central axis of the lens, and a second refracting surface extending as a smooth curve from the bottom surface to the first refracting surface. Light emitted by the semiconductor device, entering the lens through the bottom surface, and directly incident on the reflecting surface is reflected from the reflecting surface to the first refracting surface and refracted by the first refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens. Light emitted by the semiconductor device, entering the lens through the bottom surface, and directly incident on the second refracting surface is refracted by the second refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens.
The inventive light-emitting device may be efficiently coupled to shallow reflectors and to thin light guides. Secondary optics employed with the inventive light-emitting device may have relatively large illuminated areas.
In accordance with another embodiment, a lens cap comprises a bottom surface attachable to a lens, a reflecting surface, a first refracting surface obliquely angled with respect to a central axis of the lens cap, and a second refracting surface extending as a smooth curve from the bottom surface to the first refracting surface. Light entering the lens cap through the bottom surface and directly incident on the reflecting surface is reflected from the reflecting surface to the first refracting surface and refracted by the first refracting surface to exit the lens cap in a direction substantially perpendicular to the central axis of the lens. Light entering the lens cap through the bottom surface and directly incident on the second refracting surface is refracted by the second refracting surface to exit the lens cap in a direction substantially perpendicular to the central axis of the lens cap. The inventive lens cap may provide advantages similar to or the same as those described above.


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Parkyn et al., The Black Hole™: Cuspated waveguide-injectors and illuminators for LEDs; Part of the SPIE Conference on Nonimaging Optics: Maximum Efficiency Light Transfer V, Denver, CO, Jul. 1999.

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