Output Luminous Flux Research Articles

LED power consumption in joint illumination and communication system.

This paper addresses the power penalty in an illumination LED caused by visible light communication (VLC). This study models the extra power consumption of the LED by taking into account the convex relation between the dissipated electrical power versus the LED current on one hand and the concave relation between the output luminous flux versus the current on the other hand. The ratio of the output luminous flux to input electrical power, which is known the LED luminous efficacy, is analyzed considering various recombination mechanisms and their dependency on current and temperature. As examples, the rapid light fluctuations induced by Pulse Amplitude Modulation (PAM) and orthogonal frequency division multiplexing (OFDM) are analyzed for joint illumination and communication (JIC) systems. Due to the signal modulation, there is a decrease in the output light of LED. Nevertheless, the total power offered to LED is larger than without modulation and thus extra heating occurs. Moreover, particularly when burst transmission is used in communication networks, visible flicker may occur.

Numerical modeling of tubular daylighting devices

Tubular daylighting device (TDD) or light pipe is an effective way of energy saving and has been found increasing acceptance for indoor lighting. This article presents a new method to evaluate the TDD’s optical performance by the output luminous flux. The method is using position (α, d) and angular distribution of luminous flux (φ, θ, Φ) information to describe the optical properties of the TDD’s light collecting cover. With the optical information, the ray tracing simulates the output luminous flux basing on the structural and reflectivity of the light pipe. Our method makes a complete optical description of light ray passing through a top cover, thus enable the subsequent ray tracing of light pipe. As an application, lambertian beam pattern is used as light source which goes through from the cover, and then the results on various length to diameter ratios of light pipes are compared.

Investigation Into the Use of Single Inductor for Driving Multiple Series-Connected LED Channels

An investigation into the use of single inductor for driving N series-connected LED channels is presented. Each channel has a parallel-connected switch for controlling the LED channel current, as well as charging the inductor. Compared with the conventional structure having all LED channels connected in parallel and (N + 1) switches, the proposed structure has the merits of 1) requiring N switches, 2) allowing all channels to be driven concurrently in every switching cycle, and 3) being insensitive to the duration of the transition switching from one channel to another. Detailed mathematical analysis on the topological operations will be discussed. The proposed concept will be demonstrated on a two-channel structure. A prototype with two 7 W LED modules has been built and evaluated. A control mechanism that can regulate the output luminous flux and correlated color temperature without sensing the inductor current and channel currents will be discussed. Experimental results are favorably compared with theoretical predictions.

Output Properties of Transparent Submount Packaged FlipChip Light-Emitting Diode Modules

Flip chip technology has been widely adopted in modern power light-emitting diode (LED) fabrications and its output efficiency is closely related to the submount material properties. Here, we present the electrical, optical and thermal properties of flip chip light-emitting diodes mounted on transparent sapphire and borosilicate glass which have shown a higher output luminous flux when compared to the traditional non-transparent mounted LEDs. Exhibiting both better thermal conductivity and good optical transparency, flip chip LEDs with a sapphire submount showed superior performance when compared to the non-transparent silicon submount ones, and also showed better optical performance than the flip chip LEDs mounted on transparent but poor-thermal-conducting glass substrates. The correspondent analysis was carried out using ANSYS 14 to compare the experimental thermal imaging with the simulation results. TracePro software was also used to check the output luminous flux dependency on different LED mounting designs.

Concentric ring phosphor geometry on the luminous efficiency of white-light-emitting diodes with excellent color rendering property.

This study presents a novel remote phosphor design involving a concentric ring remote phosphor layer in which green and red phosphors are separated. The green and red phosphor rings were separately illuminated by blue light emitted from the light-emitting diode (LED), causing low reabsorption in phosphor-converted LEDs (pcLEDs) using green and red phosphors. The experimental results revealed that the pcLEDs with green and red phosphors showed high color rendering, indicating that the LEDs are suitable for certain medical applications and architectural lighting. Moreover, for given green/red phosphor ratio and weights of the green and red phosphors, the output power and luminous flux of the pcLED with a concentric ring remote phosphor layer were greater than those of the pcLED with a mixed remote phosphor layer. The reduction in the reabsorption of green emission by red phosphor in pcLED with a concentric ring remote phosphor layer was responsible for the high luminous flux and indicated a high correlated color temperature of pcLED.

ACU Enhancement of WLEDs Realized by Multilayer Phosphor With Convex Shape

A new package structure with three convex phosphor layers is shown to enhance the angular color uniformity based on modeling and experimental verification. The color uniformity has been improved by tailoring the phosphor concentration distribution of the three layers. The experimental measurements indicate that the deviation of angular correlated color temperature (CCT) can be reduced from 152.9, 487.2, and 586.4 K to 51.3, 55.1, and 78.7 K compared with the conventional structure at the average CCT of 4500, 5500, and 6200 K, respectively. Luminous flux and optical output power of LED packages with optimized multilayer phosphor have been measured and are reduced no more than 5% compared with the single phosphor layer packages.

White thin-film flip-chip LEDs with uniform color temperature using laser lift-off and conformal phosphor coating technologies.

We fabricated a phosphor-conversion white light emitting diode (PC-WLED) using a thin-film flip-chip GaN LED with a roughened u-GaN surface (TFFC-SR-LED) that emits blue light at 450 nm wavelength with a conformal phosphor coating that converts the blue light into yellow light. It was found that the TFFC-SR-LED with the thin-film substrate removal process and surface roughening exhibits a power enhancement of 16.1% when compared with the TFFC-LED without a sapphire substrate. When a TFFC-SR-LED with phosphors on a Cu-metal packaging-base (TFFC-SR-Cu-WLED) was operated at a forward-bias current of 350 mA, luminous flux and luminous efficacy were increased by 17.8 and 11.9%, compared to a TFFC-SR-LED on a Cup-shaped packaging-base (TFFC-SR-Cup-WLED). The angular correlated color temperature (CCT) deviation of a TFFC-SR-Cu-WLED reaches 77 K in the range of -70° to + 70° when the average CCT of white LEDs is around 4300 K. Consequently, the TFFC-SR-LED in a conformal coating phosphor structure on a Cu packaging-base could not only increase the luminous flux output, but also improve the angular-dependent CCT uniformity, thereby reducing the yellow ring effect.

A Life Prediction Model for LEDs Lamps Based on the Thermal Life Theory

The photometric, electrical, thermal and life features of LEDs are highly dependent on each other. All these factors should be considered together in order to optimize the operating point of LEDs. A thermal life theory about LEDs is developed. This theory shows the inner inks among photometric thermal and 1ife features of a LED. A life prediction model of LEDs and the relationship between output luminous flux and lifetime was found out by this theory. The life of LEDs can be predicted and find the proper operating point, at which the LED will generate the maximum amount of luminous flux in its total life cycle.

Design of Polygon Prism Optical Lens for LED Street Lamps

High-power light emitting diode (LED) develops greatly owing to its high energy efficiency, high color rendering and long life. However, it is important to design a secondary optical lens for the LED lamps to obtain a good output efficiency and light distribution pattern. The purpose of the secondary optical design for light emitting diode (LED) illumination is to rearrange the luminous flux output of LED and then achieve the desired luminous intensity distribution. In this paper, a polygon prism lens for street lamps was designed and the desired illumination was achieved. The design procedure of the polygon prism lens is presented. The simulation of the street lamps is implemented using Tracepro 7.0. The results show that the polygon prism lens can distribute the luminous flux accurately and reasonably. The luminous flux can be saved as much as possible and a rectangular distribution of luminous flux is attained.

Design of Projection Light Source for Solid Volumetric True-3D Display

The solid volumetric true−3D display requires light source with high brightness, high energy utilization rate and high frequency color field. So high−power red, green and blue LEDs with collimators were used as the projection light source. Firstly, the required quantity of LEDs was determined according to the required output luminance, the efficiency of the projector and the red, green and blue LEDs' parameters. Secondly, with the consideration of the LEDs' dimensions, light−emitting mode and output luminous flux, collimator was designed and simulation model was established. Simulation and practical measurement results both show that light source based on high−power LED meet the requirements of the solid volumetric true−3D display.

A practical method of comparing luminous intensity distributions

In the field of goniophotometry, as in many other measurement disciplines, there is an increasing need for laboratories to become ISO-17025 accredited. This involves, amongst other things, characterisation of the goniophotometric measurement for uncertainty analysis and laboratory intercomparisons. Simple comparison of the luminous intensity measurements, however, can lead to large errors where there is a steep luminous intensity gradient when the only difference between the two sets of measurements is a small discrepancy in alignment. Given the difficulty in mounting and aligning some types of luminaires, this makes uncertainty analysis and intercomparisons difficult. Furthermore, the work of several CIE Division 2 Technical Committees (e.g. TC2-62) highlights the need to compare the measurements made on both far-field and near-field goniophotometers. This paper introduces a metric for comparison of two luminous intensity distributions that isolates and removes discrepancies that arise both from misalignment and also the difference in absolute calibration scales or the luminous flux output of the source. Moreover, these discrepancies are reported as part of the metric, so that a complete comparison of the sets of measurements is possible.

Performance of ‘energy efficient’ compact fluorescent lamps

Background: Compact fluorescent lamps (CFLs) have been heralded as highly energy efficient replacements for incandescent light globes, however, there is some public dissatisfaction with the light output and colour of CFLs. Independent examination of the claims made has not been made. Compliance with the interim Australian/New Zealand Standard has not been established by any independent authority. While the total light output (luminous flux) may meet certain standards, luminous intensity distributions of some designs do differ significantly from the incandescent sources that they are intended to replace.Methods: Luminous intensity distribution, luminous flux and spectral energy distribution of CFLs claimed to be equivalent to 75-W incandescent globes and 75-W incandescent globes (pearl and clear) were measured. Luminous flux, luminous efficacy, colour rendering index, correlated colour temperature, wattage and power factor were then calculated and compared with claims made by manufacturers and requirements of the standards.Results: The sources generally complied with the requirements for luminous flux, luminous efficacy, colour rendering index and correlated colour temperature. The claim of 75-W equivalence, which is not regulated in Australia and New Zealand, is justified less than half the time. Luminous intensity distributions of biaxial CFLs are distinctly different from the incandescent lamps they purport to replace.Conclusion: CFLs generally comply with the standards set. The basis on which equivalent wattages are claimed needs to be included in the Australian and New Zealand standard because this is the measure most likely to be relied on by the public. Due to the differences in luminous intensity distribution, CFLs may not necessarily be a direct replacement for incandescent sources without some consideration.

Improved color rendering and luminous efficacy in phosphor-converted white light-emitting diodes by use of dual-blue emitting active regions

Conventional white-light sources suffer from a fundamental trade-off between color rendering index and the luminous efficacy; increasing one generally comes at the expense of the other. We demonstrate through simulation that dual-wavelength blue-emitting active regions in phosphor-converted white light sources maximize the output luminous flux while significantly increasing the color rendering ability. Our results indicate that such improvements can be achieved over a broad range of correlated color temperatures.

Development of High-power LED Lighting Luminaires Using Loop Heat Pipe

High-power LED should reject about 6 times of heat of the conventional lighting device and keep the LED junction temperature below 80°C to assure reliability and low light decay. In addition, no fan is allowed and the heat dissipation design should not interfere with the industrial design of lighting fixture and have a light weight. This thus creates an extreme thermal management problem. The present study has shown that, using a special heat dissipation technology (loop heat pipe), the high-power LED lighting luminaire with input power from 36 to 150W for outdoor and indoor applications can be achieved with light weight, among 0.96 to 1.57 kg per 1,000 lumen of net luminous flux output from the luminaire. The loop heat pipe uses a flexible connecting pipe as the condenser which can be wounded around the reflector of the luminaire to dissipate the heat to the ambient air by natural convection. For roadway or street lighting application, the present study shows that a better optical design of LED lamps can further result in power consumption reduction, based on the same illumination on road surface. The high-power LED luminaries developed in the present study have shown that the energy saving is > 50% in road lighting applications as compared to sodium light or &gt 70% compared to mercury light.

A table for experimental study of mechanoluminescent pulse pressure transducers

The procedure and results of experimental study of mechanoluminescent pressure transducers converting mechanical stress into an optical signal are described. A prototype of the mechanoluminescent pulse pressure transducer and a mechanical shock table for laboratory study of it are presented. The developed table allows one not only to fix and evaluate the output luminous flux of the transducer, but also to quantitatively determine the mechanical loading value. Comparison of recorded oscillograms of energy-emittance pulses of the transducer and results of numerical calculations demonstrates the adequacy of the used mathematical model of mechanoluminescent conversion.

Spectral and electrical performance of screw-based dimmable compact fluorescent lamps

Screw-based dimmable compact fluorescent lamps (SD-CFLs) are promoted as alternatives to incandescent lamps. This paper investigates the performance of SD-CFLs over their dimming range—including luminous flux output, colorimetric quantities, and electrical characteristics—and compares these data against the performance of incandescent lamps. The performance of SD-CFLs differs from that of the incandescent lamps they are meant to replace in several important ways, including their colour appearance, colour rendering properties, and dimming range. These and other attributes that might inhibit the widespread application of current SD-CFLs are discussed.

The measured and predicted performance of passive solar light pipe systems

Passive hollow tubes consist of a light pipe transport section with, at the upper end, some device for capturing natural light and, at the lower end, a means of distribution of light within the interior. The wider use of the systems is currently limited by the lack of quantitative design methods other than those based on empirical data. This paper presents results of laboratory and field measurement of luminous flux output and luminous intensity distribution for various configurations of passive solar light pipes. The results indicate quantitative performance and form the basis of a number of methods of performance prediction for a wide range of passive light pipe system configurations.

Analysis of Characteristics of Xenon Flashtubes by means of Experimental Equations.

Experimental equations of the tube voltage, the cureent and the flux of xenonflashtubes are established. Electrical and optical characteristics are calculated by these three equations and are discussed for different applied voltages and tube lengths.The following results are obtained:1. The maximum current density, the maximum luminous flux and light output increase with an increasing applied voltage and a shorter distance between electrodes.2. Duration of more than half flux of its maximum being maintained decreases with an increasing applied voltage and a decreasing the tube length.3. The efficiency increases with an increasing applied voltage and a decreasing tube length. The rate of its increase becomes smaller as the tube length decreases below 5cm.

Incandescent Lamp as a Control System Element

Three tungsten-filament lamps have been investigated with particular attention given to determining the applicability of the standard linear transfer function concept to these basically nonlinear elements. The lamps cover a power range of from 14 mW to 14 W. They are the Kay L12–12 Pinlite, 12 mA at 1.2 V, the No. 47, 150 mA at 6 V, and the No. 94, 1.2 A at 12 V. The greatest range of operation linear to within 5% is determined from output luminous flux versus input voltage characteristics. Allowable flux variation about a dc bias point selected in the 5% linear range is found to be at least ±40%. Bode type amplitude-phase characteristics are measured for the three lamps. Conventional linear transfer functions are deduced from the Bode plots, linear approximations are constructed, and the resulting composite approximations are compared to the empirical characteristics and found to be satisfactory for design usage. Deviations from linear operation are investigated, and in the case of the lamp bias, found to impose some restrictions. An operating lamp control system designed on the basis of the above described work has been built and is discussed.