The development of high power white LED has become the priority of most major optoelectronics companies. Germany based OSRAM, LUMILEDS of Philips and Nichia of Japan are the big players in this field. You will discover the detail design and comprehensive ray tracing simulation results of high power LED collimator in this article.
The photo below shows a typical high power LED available in the market.
A typical low power LED could only generate 1~3 lumen when driven at 30mA. A high power LED could be driven at 700mA and generate 60 lumen. Lumen is a unit of luminous flux equal to the amount of light given out through a solid angle of 1 steradian by a point source of 1 candela intensity radiating uniformly in all directions
This article will illustrate the design and simulation of high power LED collimator. A collimator is used to focus the light emitting from LED into a narrow beam or small beam radius. This will normally increase the radiant intensity of the new beam spot .
The Zemax Optics simulation software was utilized to design the high power white led radiant intensity lambertian profile. As shown by the figure below, a high power LED model has been constructed using the Zemax Non-Sequential Components -"Standard LENS" and the source is using "Source Radial".
The advantage of using the "Source Radial" is that we are able to input the radiant intensity profile of the LED by refering to the actual LED datasheet. For example, the lambertian radiation profile from a high power LED datasheet is shown in the figure below.
From here, we could input the data to the "Source Radial" property. For example, at 0 Degree the value is 1, at 10 Degree the value is 0.98, at 20 Degree the value is 0.95, at 30 Degree the value is 0.9, at 40 Degree the value is 0.85 and so forth until we input the value at 90 Degree is close to 0. As the radiant pattern is symmetrical, we just need to input it on the positive axis.
Once we have completed this, we checked the ray tracing results of this newly created high power LED light source. A detector of a size of 20cm x 20cm is place at distance of 20cm from the LED. Then, we begin the ray tracing with the number of analysis ray set as 1 million.
After the ray tracing simulation completed, the detector image will shows the following results. The detector image setting is "Radiant Intensity". This shows the LED light intensity level from high -in red color to low-in blue color.
We also display the radiant intensity in the cross section format as shown below. It is clear that we are able to obtain a close proximity of the lambertian radiant pattern between the datasheet and the simulation results.
Next, we change the detector setting to "Incoherent Irradiance". This will shows the actual flux or light power that fall onto the detector. This is the image when you look at a black color wall being lighted up by this high power LED.
Once we have comfirmed the light source is meeting our design criteria, we will proceed to construct the collimator. The collimator design and dimension is shown on the figure below.
The 3D layout of the collimator is shown on the figure below. There is a hollow tube in the middle of the collimator and a aspheric opening at the bottom of the collimator to house the high power LED.
And next we will place our LED inside the dome portion of the collimator. The figure below shows the ray trace from the power LED to the collimator.
After we have completed this, we checked the ray tracing results of the high power LED light source + the collimator. Again, one detector of a size of 20cm x 20cm is place at distance of 20cm from the LED. Then, we begin the ray tracing with the number of analysis ray set as 1 million. The figure belows shows the irradiance with and without the collimator. The figure with a small beam spot is the irradiance with collimator.
And the figure below is the detector view without the collimator has a wide spread of beam spot.
Next, we would want to compare the peak intensity between the collimated light source and the non collimate light source. This will let us know the increment of light intensity by using the collimator. As shown in the figure below, the peak intensity of the collimated irradiance is 0.0125 W. For the non-collimated irradiance, the peak irradiance is 0.000751 W. The magnification of irradiance is 0.0125 / 0.000751 = 16.6 times.
A high power LED light source with an original 55 Lumen brightness, will be able to achieve the collimated 16.6 x 55 = 913 Lumen brightness !
With the emergence of high power white LED and the proliferation of light guide and collimator, it has opened up a new dimension for future illuminance landscape. Automotive head lamp, mobile phone mini projector, MR11 or MR16 lamp replacement, camera phone flash and LCD backlighting are the major applications that will become the fortress of high power LED. -End-
