LED light

A laboratory human factors experiment was conducted to understand the color rendering properties of various LED-based reading lights. Human subjects rated their preference for a given scene illuminated by a test light source compared to an identical scene illuminated by a reference light source. In another experiment the same subjects viewed and rated the scenes individually when illuminated by a test light source. LED-based light sources were preferred more than halogen and incandescent light sources for overall color appearance. However, phosphor-based white LED light sources were rated poor for the appearance of human skin tones. This study shows that RGB mix white LED light sources have the best overall characteristics to be used as reading or task lights. This study has shown that CRI has no correlation to peoples' color preference. Therefore, the authors of this manuscript do not believe that CRI should be used as a target metric for color rendering properties in the development of solid-state light sources because it could negatively impact overall performance. A better metric is long overdue to quantify light source color rendering and preference properties.

The efficiency of LED lights is approaching that of fluorescent lamps. LED light sources are finding more applications than conventional light bulbs due to their compactness, lower heat dissipation, and most importantly, real-time color changing capability. Accurate control of colors for RGB LED lights is a challenging task, which includes optical color mixing, color light intensity control and color point maintenance due to LED junction temperature change and device aging. In this paper , we present a LED junction temperature measurement technique for a pulse width modulation (PWM) diode forward current controlled RGB LED lighting system. The technique can control the color effectively without the need for using expensive feedback systems involving light sensors. Performance of chromaticity and luminance stability for a temperature compensated RGB LED system will be presented.

We present a study by optical ray-tracing in order to determine the impact of an inhomogeneous phosphor distribution in the color conversion elements (CCE) of phosphor-conversion- based white LED light sources. It turns out that in particular the color temperature and its angular variation, but also the flux-output are highly sensitive towards phosphor distribution variations.

This study observed the effect of different LED light colour on the behaviour and fear responses of broilers. In experiment 1, 400 broilers were placed into eight different light treatments. In experiment 2, six different light colours with five different age groups were considered. In experiment 1, use of a red and red–yellow mixed light significantly increased walking behaviour. Consequently, sitting and standing behaviour were found to be wavelength dependent, whereby short wavelength (blue, green–blue) treated birds spent more time sitting and standing than that under long wavelength (red, red–yellow). Consistently in experiment 2, birds spent more time feeding under the green treatment than with other treatments. Walking behaviour was significantly decreased and sitting and standing behaviour was increased under the blue light. Age also influenced the behaviour of broiler: young birds were more active than older birds. In addition, ground pecking and wing stretching behaviour were influenced by the wavelength of the light. Time of day did not influence the behaviour of the broilers. Under the red and red–yellow light treatments, birds spent longer in tonic immobility. Thus, the results suggest that red and red–yellow light activated the broiler's movement and fear responses while blue and green-blue decreased the movement and they spent more time sitting.

Recent advances in ubiquitous technologies facilitate location-aware and power-aware systems that can provide predefined services. Recent research efforts are based on control mechanisms for standby power reduction. Conventional systems are only designed for power reduction of the consumer electronics. However, due to their architectural limitations, the recent systems are not flexible with respect to LED light control for power reduction. We need to consider efficient autonomous power control based on intelligent devices and the power-aware service prediction in networked environments. In this paper, we propose a power-aware LED light enabler with light sensors, motion sensors and network interfaces. The LED light enabler also communicates with context-aware middleware using an intelligent power gateway that adaptively determines the optimal power control by analyzing user living patterns using sensing data obtained by devices. Our power-aware LED light enabler with adaptive middleware dynamically reconfigures the power-aware services. The proposed adaptive middleware facilitates the learning mechanism which analyzes the illumination and the user activity, and controls the LED lights only when users exist around the devices. Our enabler reduces power consumption up to 58% in comparison to a basic lighting system at the real office testbed.

Today, all count words are about how to enhance the electrical grid reliability during the peak instant. The direct solution for the grid is to cut off some loads to keep its stability. One of these loads is the street lighting especially during the summer period. This paper proposes an energy-free system for street lighting as there is no power demand from the grid. A standalone solar street LED light system is proposed. The proposed system consists of a PV panel, storage system, LED lamp, power conditioning system (PCS) and the controller which can manage the power direction and system operation. Using LED in lighting applications has many advantages compared to other lamp. It is very efficient (very high efficiency lighting source) lamps and cost effective (the life time is very long compare to other lamps). In additions to, it needs low dc voltage source to be operated. The storage system will be charged during the day time using the available sunlight. On the other hand, during the night time the controller will give a signal to the system to connect the LED lamp to be ready for use. Since the LED needs a low dc voltage to be operated, a simple dc-dc converter will be enough for this system resulting in decreasing the cost of the overall system. Moreover, a low cost microcontroller is proposed to handle the operation of the whole system. Applying this idea in the Egyptian streets enables the reduction of more than 50 % of the total required energy by HID lamps that enable the use for small PV system. By this proposed system, streets can be illuminated with lower power lamps, no operating costs, no CO2 emissions, grid energy-free and environmentally friendly. Moreover, the proposed solution can solve the Egyptian peak point crisis of load demand.

Because of advantages such as long lifetime, low power consumption, and no mercury containing, LEDs are widely used in a variety of general-purpose illumination applications. There are two different approaches for generating white light with LEDs. The first one is the combination of phosphors excited by blue or UV LED emission, the other one is mixture of multi-color LEDs Without the power loss in the down conversion process of the white LED using phosphors, a higher efficiency and flexible option can be done with the mixture of multi-color LEDs. Questions arise on how the spectra of the mixture of colored LED designed are for good color rendering performance, more output lumens and better luminous efficiency. A lot of papers discuss the different spectrum combinations of multicolored LEDs which yield light with maximum efficacy, luminous flux and CRI, at the desired corrected color temperature, but most of them use the spectral power distribution of a model LED to calculate the luminous efficacy, luminous flux and CRI, and get the best combination as request. But as most people know, the spectral power distribution of a real LED will vary with ambient temperature, forward current and effect of aging, so simulation of the luminous efficacy, luminous flux and CRI will get some problems in practical. On the other hand, the finding of a better luminous efficacy of the mixture of colored LED can provide the best suggestion when the LED manufacturers try to select commercial LED chips to manufacture colored LED light sources. We setup a system with integrating sphere, spectrometer and four independent PC controlled powermeters, which can get the data of luminous flux, CRI and luminous efficiency of light sources automatically with different input power. Using the database from the system and simulations, we can analyze the optical and color characteristics of the mixture of colored LED light source, even the RGB LED (red, green and blue chips in one package). Then the selection of the combination of the LED chips for the mixture of colored LED light source, for generating more luminous flux, better color rendering index and luminous efficiency should be good.

Several life cycle assessments of light sources have been conducted during last two decades. This article compares their methods and results, and identifies the challenges. Light-emitting diode (LED) is considered as an environmentally friendly solution for lighting. The LEDs have the potential to be the most environmentally friendly light sources not least because of their increasing luminous efficacy and long lifetime. However, there are neither detailed data nor a profound life cycle assessment of a range of LED lighting products to undisputedly prove their environmental performance. Currently, the total life cycle environmental impacts of LED light sources are not known due to uncertainties and lack of peer-reviewed

As an alternative to conventional lighting systems, light emitting diode (LED) has been demonstrated to be an artificial flexible lighting source for commercial micropropagation. The objective of this study was to determine the effects of different LED light quality on in vitro shoot proliferation and growth of Vanilla planifolia. To evaluate shoot proliferation, axillary bud cuttings (3 to 5 mm in diameter) of V. planifolia were used as explants and cultivated on Murashige and Skoog basal medium supplemented with 9.55 µM of 6-benzylaminopurine. To evaluate in vitro growth, unrooted shoots (2 cm in length) were used as explants cultivated on Murashige and Skoog basal medium without plant growth regulators. All explants were exposed to a 16 h photoperiod for 60 days under five different lights: fluorescent lamp, white LED, blue LED, red LED and blue plus red LED mixtures (Blue + Red = 1:1). The results indicated a clear increase in the number of shoots per explant under Fluorescent Lamp, White LED and Blue+Red LED light; these treatments produced more than 10 shoots. Shoot length was more than 3 cm in cultures under Blue, Red and Blue+Red (1:1) LEDs, and less than 3 cm in Fluorescent Lamp and White LEDs. Our results also showed that fresh weight, dry weight and dry matter were greatest in shoots under Blue+Red LED light. For shoot growth, plant height, number of leaves, number and length of roots, fresh weight, dry weight, dry matter and chlorophyll content were greater under Fluorescent Lamp and White LED. In conclusion, White or Blue+Red LED light may be used as an alternative light source for shoot proliferation, while White LED may be used for growth in vitro. These results demonstrate the effectiveness of light qualities using LEDs for micropropagation of V. planifolia. Key words: Light quality, micropropagation, orchid, chlorophyll.

Along with the high energy-efficiency potential, light-emitting diode (LED) lighting provides the possibility for spectrum control. Our study presents the original data on the influence of LED light spectrum quality on the growth and macro- and micro-nutrient uptake of lettuce (Lactuca sativa L. cv. Frillice) plants cultivated in indoor conditions and without daylight. Four LED light spectral combinations were investigated using conventional high-pressure sodium (HPS) lighting as a control. In general, the LED light spectra were more favourable than the HPS light spectrum for promoting the growth and nutrient uptake of plants. In particular, the light spectrum provided by the combination of the far-red, deep-red and blue LEDs had the highest growth and nutrient uptake indices. This spectral combination particularly enhanced the uptake of potassium, calcium and magnesium in comparison to control plants grown under conventional HPS lamps. The uptake of iron and zinc were significantly influenced by the spectral changes of the red and blue light.