LED collimation optics with improved performance and reduced size

DETAILED DESCRIPTION This invention represents an improvement in the performance of the Flat top Tulip Collimator disclosed and claimed in our co-pending application Ser.
No.
09/415,833 referred to above in terms of reduced size, beam divergence, beam uniformity, and to some degree efficiency.
Moreover, it allows a wider variety of choices in optimizing various performance characteristics at the expense of others.
This in turn allows more flexibility in the design process, leading to improvements in the various applications that employ the LEDs and collimation optics.
According to the invention, the various optical surfaces of the collimation optics are defined according to one or more constructive rules in order to reduce the angular errors, which result from the finite (i.
e.
non-infinitesimal) LED source size.
The advantages of the present invention are described in the description that follows in terms of five main characteristics: (1) the beam divergence angle, (2) the exit aperture diameter d.
sub.
e, (3) the overall height h, (4) the spatial uniformity of the exit beam, and (5) the efficiency .
eta.
.
Since .
theta.
and d.
sub.
e are ultimately related by a fundamental theorem--the conservation of etendue, the initial description is geared to one fixed value of d.
sub.
e, namely 30 mm.
This is arbitrary and for illustrative convenience only, and in no way limits the generality of possible design choices.
In the discussion that follows, performance will be described in relation to a 30 mm flat top tulip collimator with a 1 mm square LED chip in the standard LED package with a 2.
75 mm radius hemispheric dome lens.
This will be referred to hereinafter as the "Reference Collimator 20" and is illustrated in FIG.
1A.
Additionally, we take as the "beam divergence angle" the cone half-angle that envelopes 90% of the beam, and we refer to this angle hereinafter as angle .
theta.
.
sub.
90 %.
An object of this invention is to gain improvements in one or more desirable characteristics of a flat top tulip collimator without sacrificing performance in other areas