LED Flashlight

Light Emitting Diodes, or LEDs, have surpassed incandescent light sources in recent years for most applications. Benefits of the LED include compact size, high power efficiency, and a long lifespan [1]. LEDs also have undesirable qualities that optical engineers must address, such as the need for color mixing and collimation. In this example we look at a simple example of a LED flashlight.

FRED Model

The flashlight modeled in this example consists of three white LEDs. The LED geometry is based on the basic LED sample file provided with the FRED installation. The LEDs are arranged in a triangular configuration. A phosphor-based white light spectrum is created and assigned to the LED source.

The flashlight body is a composite structure consisting of two basic shapes (a rod and a pipe). Eeach shape is created with the desired dimensions and positioned making sure to leave no gaps between the rod and pipe.

Figure 1. Left: Flashlight model in FRED. This model consists of the body, faceted reflector, and arrangement of three white-light LEDs. Right: Schematic ray trace of the flashlight. Rays reflected by the faceted reflector are shown in red.

To increase optical efficiency, a faceted reflector can be placed just behind the LEDs. This reflector is created using a “Custom Element” consisting of two components: a curve and a surface. The segmented curve requires (X,Y,Z) coordinates of each breakpoint and is used to define the radial profile of the reflector This curve has parabolic shape in the X-Z plane, with Z values proportional to X^2. Then this segmented curve is assigned as the Generatrix Curve for the surface of revolution. Exact parameters of the segmented reflector curve and surface are shown in Figure 2, along with a schematic of the finished reflector.

Figure 2a. Left: Breakpoint coordinates for the segmented curve. Right: Parameters for the surface of revolution.

Figure 2b: Faceted reflector modeled in FRED. The segmented curve is shown in red.

Irradiance, intensity, and color image of the flashlight are analyzed at various distances (Figure 3). Collimation of emitted light can be optimized by adjusting the shape of the parabolic faceted reflector.

Figure 3. Color image from flashlight illumination at two different distances: 0.1 m (left) and 0.5 m (right).

The associated FRED file can be downloaded here: led-flashlight.frd

[1] “New Report Explores the Global Industrial and Commercial LED Lighting Market to Be Propelled by Government Prohibition on the Use of Incandescent Lamps.” WhaTech. September 28, 2015. Accessed September 29, 2015. https://www.whatech.com/market-research/consumer/97505-global-industrial-and-commercial-led-lighting-market-to-be-propelled-by-government-prohibition-on-the-use-of-incandescent-lamps.