For optical designs, the choice of direct or indirect configuration is determined by a number of competing factors and by considering the priorities of the lighting solution, writes Andreas Bielawny. The LED, the solid-state light source of the future, differs in manyaspects from For all, let us consider only one aspect: LEDs are surface emitters, and because of the planar substrates on which they are currently deposited, the die generally exhibits a half-space emissioncharacteristic.
The terms, all LED applications can generally be divided into two groups: direct and indirect (see Fig. 1). The terms direct and indirect describe the relation between the LED and its secondary optic components, or the light target (the main optical axis). Term direct (as for direct light/flux)is also used to emphasize the fact that LEDapplications use the flux from the primaryoptic lens of the emitter to create the lightdistribution.
Direct: A direct optical configuration ischaracterized by the alignment of the optical axis of the emitter(s) with the main opticalaxis of the light. This need not evenbe coaxial. It can also be considered an issue of the direct visibility of the emitter (from a point of Such arangement would be addressed as direct type, but they strongly restrict the visibility angles of the emitter, which is observed only through secondary optics.
Indirect: In contrast to the direct configuration, an indirect optical configuration will always prevent the emitter from being observed directly. Instead, the flow of light will be intact completely by secondary optics, such as free-formreflectors. In the archetypicalrepresentation of an indirect configuration, the optical axis Of the emitter will be antiparallelto the optical axis of the light (the reflector); for example, a perfectreverse orientation. Any semi-direct solutions are also possible.
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This article was published in the Sept/Oct 2009 issue of LEDs Magazine.To read the full version of this article, please visit our magazine page, where you can download FREE electronic PDF versions of all issues of LEDs Magazine.
You can also request a print copy of LEDs Magazine (available by paid subscription) and sign up for our free weekly email newsletter . About the Author Andreas Bielawny ( ) is an Optical Engineer withBrandenburg GmbH ( ), Paderborn , Germany.
The terms, all LED applications can generally be divided into two groups: direct and indirect (see Fig. 1). The terms direct and indirect describe the relation between the LED and its secondary optic components, or the light target (the main optical axis). Term direct (as for direct light/flux)is also used to emphasize the fact that LEDapplications use the flux from the primaryoptic lens of the emitter to create the lightdistribution.
Direct: A direct optical configuration ischaracterized by the alignment of the optical axis of the emitter(s) with the main opticalaxis of the light. This need not evenbe coaxial. It can also be considered an issue of the direct visibility of the emitter (from a point of Such arangement would be addressed as direct type, but they strongly restrict the visibility angles of the emitter, which is observed only through secondary optics.
Indirect: In contrast to the direct configuration, an indirect optical configuration will always prevent the emitter from being observed directly. Instead, the flow of light will be intact completely by secondary optics, such as free-formreflectors. In the archetypicalrepresentation of an indirect configuration, the optical axis Of the emitter will be antiparallelto the optical axis of the light (the reflector); for example, a perfectreverse orientation. Any semi-direct solutions are also possible.
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This article was published in the Sept/Oct 2009 issue of LEDs Magazine.To read the full version of this article, please visit our magazine page, where you can download FREE electronic PDF versions of all issues of LEDs Magazine.
You can also request a print copy of LEDs Magazine (available by paid subscription) and sign up for our free weekly email newsletter . About the Author Andreas Bielawny ( ) is an Optical Engineer withBrandenburg GmbH ( ), Paderborn , Germany.
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