Understanding Power LED Lifetime Analysis
How intuitive graphical data sets help lighting designers accurately predict power LED
reliability in different operating environments
When designing LED-based lighting systems, engineers need to understand LED lumen
maintenance and mortality in similar terms to those used when designing with conventional light sources. However, comparable data has been nearly impossible to find. In addition, designers need extra information to predict the lifetime of LEDs under a variety of operating conditions. A number of techniques to predict LED lifetimes have been proposed, but these have not been sufficient to generate the clear and unambiguous data that lighting engineers can use easily. This white paper provides lighting designers with an understanding of a new tool introduced by Philips Lumileds Lighting Company that simplifies the process allowing full flexibility in design options. This one tool provides designers with information that they need to make decisions about product lifetimes, driver constraints, number of LEDs required, and thermal management.
Philips Lumileds

Red, Green and Blue LED based White Light Generation: Issues and Control
The recent improvements in high-power light emitting diodes (LED) technology with 100+ lumens per LED chip and efficacy exceeding that of incandescent lamps, brings the solid-state lighting close to a reality. An LED light source made of Red, Green and Blue (RGB) LEDs can provide a compact light source with unique features such as instant color variability. However, the white light generation using many compact, discrete RGB light sources has the following issues: uniform spatial light mixing and distribution, white color point maintenance and thermal management. Specifically, the white color point maintenance is a stringent requirement in many applications. Meeting this requirement is a severe challenge due to the variation in the optical characteristics of the RGB-LEDs with temperature, time and forward current and the spread in the LED performance. This results in 1) an unacceptably high variability in white light color point and 2) difficulties in manufacturing reproducible LED lamps.
In this paper, we highlight the issues that introduce the variability in the color point and present feedback control schemes to overcome these problems. We also show the results of experiments and theoretical modeling for practical control systems.
Advance Transformer

Red, Green and Blue LED-based White Light Source: Implementation Challenges and Control Design
The recent improvements in high power light emitting diode (LED) technology with 100+ lumens per LED chip bring solid-state lighting close to reality. Combining red, green and blue (RGB) LEDs can provide a compact white light source with unique features such as instant color variability. However, the implementation of an RGB-LED light source has numerous practical issues such as sensor placement, LED driving, control design and stability with temperature and time. This can result in lamp operation that may not meet the spatial, color maintenance and perception requirements of many applications.
In this paper, we highlight the practical issues and present solutions using an RGB-LED light engine as an example. The spatial mixing, sensor placement, and control system design for
the light engine are discussed and experimental results are provided.
Advance Transformer

Red, Green and Blue LEDs for White Light Illumination
The rapid improvement of the white light efficacy achievable with light-emitting diodes (LEDs) opens up new opportunities in the general illumination market. An LED light source made of red, green, and blue LEDs (RGB-LEDs) can provide the unique feature of color variability, allowing the user to select the desired color point of the lamp. The white light color accuracy required in the general illumination market is a challenge for LEDs. The variation in lumen output and wavelength for nominally identical LEDs and the change in these parameters with temperature and time result in an unacceptably high variability in the color point of white light from RGB-LEDs.
In this paper, we show that these problems can be overcome with suitable feedback control schemes that can be implemented in a practical LED lamp. We present results of experiment and theoretical modeling that shows the performance that can be achieved with a number of different control schemes.
Advance Transformer

Optimizing Illumination for Linescan Vision Systems
Illuminators for machine vision have historically been designed by adapting readily available, mass-produced illumination technologies to suit individual machine vision applications. These standard illumination sources, e.g. fluorescents and incandescents, were originally developed for mass-market deployment in domestic automotive and display technologies. While the main advantage of these lighting sources is low cost, they are often not suited for scientific or instrumentation vision systems.
This white paper looks at the particular case of linescan machine vision applications and argues that users select a no-compromise illumination method in order to meet the demands of today’s sophisticated machine vision systems. Furthermore, the paper will demonstrate that StockerYale’s COBRA LED technology provides the machine vision designer with increased performance, reliability, and longevity, over traditional illumination techniques.
StockerYale

Liquid Cooling of Bright LEDs for Automotive Applications
With the advances in the technology of materials based on GaN, high brightness white light emitting diodes (LEDs) have flourished over the past few years and have shown to be very promising in many new illumination applications such as outdoor illumination, task and decorative lighting as well as aircraft and automobile illuminations. The objective of this paper is to investigate an active liquid cooling solution of such LEDs in an application of automotive headlights. The thermal design from device to board to system level has been carried out
in this research. Air cooling and passive liquid cooling methods are investigated and excluded as unsuitable, and therefore an active liquid cooling solution is selected.
Several configurations of the active liquid cooling system are studied and optimisation work has been carried out to find an optimum thermal performance.
Tyndall National Institute - Schefenacker Vision Systems GmbH

The Advantages of LUXEON Flash Power LEDs versus Xenon Technology for Digital Photography
Philips Lumileds

Advantages of Power LEDs in Cameraphone Applications
Philips Lumileds