Hardware implementation of digitaly controlled colour temperature tuneable white light

A white LED complemented by cyan and red LEDs is a good candidate for achieving high colour rendering at low correlated colour temperatures. This is usually very difficult with commercially available white LEDs. In addition, the system is able to replace incandescent lighting in many applications; for example, the lighting for museum display cases. To investigate and optimize the colour and light distribution properties, both spectral and geometrical modelling are used. Mapping of the possible combinations of LEDs is used to locate the optimal solutions within the colour gamut, with emphasis on chromaticity and colour rendering indices. A geometric optical model is used to design and optimize the homogeneity of the colour and light intensity distribution as a function of angle. The resulting system produces diffused homogeneous white light with a tunable correlated colour temperature from 2000 K to 2400 K. Within this range the white light is characterized by a high general colour rendering index (Ra > 90), special colour rendering indices for saturated red objects (R9 > 85), and low chromaticity distance (Duv) from the Planckian locus (Duv < 2 × 10−3).

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Operating Control of Photobiological Safety of LED Luminaires

Light & Engineering ◽

10.33383/2018-106 ◽

2019 ◽

pp. 37-42

Author(s):

Alexander V. Karev ◽

Dmitry S. Dmitry S. Lyoskin

Keyword(s):

White Light ◽

Laboratory Testing ◽

Risk Level ◽

International Electrotechnical Commission ◽

Special Equipment ◽

Experimental Assessment ◽

Russian Market ◽

Colour Temperature ◽

Safety Requirements ◽

Hazard Level

Photobiological safety has become an integral part of safety requirements to general use luminaires including during certification. In that context, the necessity to control this parameter in the course of designing and manufacturing of lighting devices (luminaires) as well as sales of imported devices in the Russian market has increased dramatically. In the meantime, experimental assessment of this indicator in accordance with requirements of IEC62471Р¦2013 standard is rather hard requiring application of special equipment and certified personnel. This circumstance makes operating control of photobiological safety by manufacturers almost impossible. The foreign practice of application photobiological safety-related standards confirms this problem. In 2014, International Electrotechnical Commission has published a handbook for application of the standard provisions, which significantly simplifies the procedure of such assessments: IEC/ TR62778:2014. The article describes the method of application of provisions of this handbook as an operating tool in the course of development of general use LED luminaires with white light LED. The provisions consist of assessment of hazard level in terms of illuminance in the area of the most possible location of a spectator and colour characteristics of a light source. A calculation method of risk level assessment on the basis of spatial light distribution and correlated colour temperature of LED luminaires is proposed, the results of calculations are compared with the results of laboratory testing.

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Interactive effect of illuminance and correlated colour temperature on colour preference and degree of white light sensation for Chinese observers

Optik ◽

10.1016/j.ijleo.2020.165675 ◽

2020 ◽

Vol 224 ◽

pp. 165675

Author(s):

Yu Wang ◽

Qiang Liu ◽

Wenyu Gao ◽

Michael R. Pointer ◽

Zheng Huang ◽

...

Keyword(s):

White Light ◽

Interactive Effect ◽

Colour Preference ◽

Colour Temperature

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Low-Cost Extra-Low Voltage LED Dimmer for Tuneable White Lighting

Elektronika ir Elektrotechnika ◽

10.5755/j01.eie.25.3.23675 ◽

2019 ◽

Vol 25 (3) ◽

pp. 43-49

Author(s):

Roman Hrbac ◽

Tomas Mlcak ◽

Vaclav Kolar ◽

Tomas Vantuch

Keyword(s):

White Light ◽

Low Voltage ◽

Low Cost ◽

Light Output ◽

Electrical Performance ◽

Light Sources ◽

Colour Temperature ◽

Lighting Systems ◽

Module Efficiency ◽

The Right

The colour appearance of light sources has a major impact on how people perceive space. With LED illumination lighting, the colour output can be tuned to virtually any perceivable colour, including any hue of white light. It has been established that the right shade of white light during the 24-hour day cycle has a positive effect on the human body's biological system. For this reason, it is very important to focus on the development and application of new lighting systems that have dynamically variable light outputs in order to imitate the sunlight. Circadian regulation is most responsive to short-wavelength light (460 nm = blue colour). This paper describes the development of a low-cost extra-low voltage LED dimmer for tunable white lighting systems aiming to achieve maximum electrical performance and light-output. This dimming module has two independent LED control channels and allows for a variable colour temperature control from warm white to cold white light. Experimental results of the dimming module efficiency measurements, correlated colour temperature (CCT), colour rendering index (CRI), illuminance and power consumption of the luminaire depending on the duty cycle for different control frequencies (200 Hz, 1.5 kHz, 5 kHz, 10 kHz and 20 kHz) are presented. The paper further describes the principle of creating control curves for an independent regulation of correlated colour temperature and illuminance. In the form of a table, the control curve outputs may be uploaded into a microcontroller. The paper details the construction, function and the advantages of this LED dimmer prototype.

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Thermally Stable Encapsulation Material Based on Green and Red Lanthanide Phosphor for White Light Emitting Diodes

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.815.182 ◽

2015 ◽

Vol 815 ◽

pp. 182-187

Author(s):

Wedianti Shualdi ◽

Nik Mohd Azmi ◽

Nurul Huda Yusoff ◽

Nor Adhila Muhammad ◽

Khairuldin Mohd Isha

Keyword(s):

White Light ◽

Sol Gel ◽

Junction Temperature ◽

Integrating Sphere ◽

Light Emitting ◽

Colour Temperature ◽

Uv Led ◽

Lanthanides Complexes ◽

The Stability ◽

White Light Emitting Diodes

This study reported thermal stability of hybrid sol-gel encapsulation materials doped with lanthanides complexes for generating white light. Red and green lanthanide phosphor, Eu (tta)3phen and Tb (4DBBA)3TPPO were incorporated into VTES:TEOS hybrid sol-gel and dispensed into 360 nm to 390 nm UV LED packages. Thermal properties of developed encapsulation material were analysed by TGA. A thermal aging test up to 96 hours was done to check the stability of developed encapsulation material towards UV LED junction temperature of 120°C and the luminescence properties changes was observed using photoluminescence measurement. To check the encapsulation material stability on forward voltage, the operation voltage has been increased from 3.0V to 4.0V. The photometric measurement were recorded using integrating sphere for the properties of Colour Rendering Index (CRI), colour temperature and Commission Internationale de L’Eclairge (CIE) colour coordinates. Based on the results, developed encapsulation material produced white colour with CIE colour coordinate of (0.32, 0.35), CRI up to 75 and colour temperature around 6000K.

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Influence of Peak Wavelengths on Properties of Mixed-LED White-Light Sources

Advances in OptoElectronics ◽

10.1155/2010/437564 ◽

2010 ◽

Vol 2010 ◽

pp. 1-8 ◽

Cited By ~ 2

Author(s):

Snjezana Soltic ◽

Andrew N. Chalmers

Keyword(s):

Light Source ◽

White Light ◽

Light Sources ◽

Peak Wavelength ◽

White Light Source ◽

Luminous Efficacy ◽

Colour Temperature ◽

Colour Rendering

The purpose of this investigation is to quantify the influence of the peak wavelength shifts in commercially available LEDs on the characteristics of the mixed-LED white-light sources. For this purpose, a tetrachromatic spectrum was optimized and then subjected to deviations in the peak wavelengths. A total of 882 combinations of peak wavelength values were evaluated, and the results are reported in terms of correlated colour temperature, colour-rendering properties, and radiant luminous efficacy. The results show that there can be significant changes in the characteristics of the source under these conditions. Such changes are highly likely to present problems when dealing with applications where an effective and accurate white-light source is important.

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Evaluation of a daylight-responsive, iterative, closed-loop light control scheme

Lighting Research and Technology ◽

10.1177/1477153519853318 ◽

2019 ◽

Vol 52 (2) ◽

pp. 257-273

Author(s):

PK Maiti ◽

B Roy

Keyword(s):

White Light ◽

Laboratory Testing ◽

Closed Loop ◽

Light Emitting Diode ◽

Light Control ◽

In Situ Testing ◽

Light Emitting ◽

Colour Temperature ◽

Control Scheme

In this paper an iterative, closed-loop light control scheme is proposed and evaluated by a white light emitting diode-based, daylight-responsive luminaire to follow the time-varying pattern of correlated colour temperature and illuminance of a daylight scene. The proposed control scheme functions primarily with the response signals of two RGB colour sensors, viz., a daylight sensor to monitor the daylight scene at the window plane and an internal light sensor to monitor the light scene created by the test white light emitting diode luminaire. The control scheme controls the lumen delivery of individual light emitting diode arrays of the test luminaire by adjusting the duty cycles to follow the instantaneous correlated colour temperature of daylight and at the same time to respond to the variation of window plane illuminance in the reverse pattern. Evaluation is conducted by laboratory testing and in situ testing. The maximum deviations in correlated colour temperature, illuminance and chromaticity from the required values under laboratory testing and in situ testing are found to be [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text], [Formula: see text] respectively, which establish the acceptable performance of the proposed iterative light control scheme.

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Colour preference, naturalness, vividness and colour quality metrics, Part 3: Experiments with makeup products and analysis of the complete warm white dataset

Lighting Research and Technology ◽

10.1177/1477153516669558 ◽

2016 ◽

Vol 50 (2) ◽

pp. 218-236 ◽

Cited By ~ 18

Author(s):

TQ Khanh ◽

P Bodrogi

Keyword(s):

Linear Combination ◽

White Light ◽

Light Sources ◽

Complex Phenomenon ◽

Cosmetic Products ◽

Colour Preference ◽

Colour Temperature ◽

Cognitive Components ◽

Warm White Light ◽

Moderate Range

Light source colour quality is a complex phenomenon with several visual and cognitive components. Subjective colour preference, naturalness and vividness assessments of reddish cosmetic products in a viewing booth lit by light sources with a correlated colour temperature of 3200 K and to 550 lx were analysed and modelled by a new combined colour quality formula – a linear combination of a colour fidelity index and a measure of chroma change. Results of the warm white light sources described in all three parts of this work were merged. They were modelled by optimising the parameters of the same formula. The formula supports multi-LED light sources with moderately accentuated local spectral maxima to enhance object chroma over a moderate range.

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LED chip-on-board package with high colour rendering index and high luminous efficacy

Lighting Research and Technology ◽

10.1177/1477153517701535 ◽

2017 ◽

Vol 50 (3) ◽

pp. 482-488 ◽

Cited By ~ 2

Author(s):

Z Zhou ◽

H Wang ◽

J Zhang ◽

J Su ◽

P Ge

Keyword(s):

White Light ◽

Power Distribution ◽

Spectral Power ◽

White Led ◽

Phosphor Powder ◽

Phosphor Layer ◽

Luminous Efficacy ◽

Colour Temperature ◽

Spectral Power Distribution ◽

Colour Rendering

Existing white light LED technology uses a blue light LED chip to stimulate a phosphor powder to form white light. The phosphor layer on the surface directly affects the colour rendering index, luminous efficacy and colour temperature of the LED. We propose a high power, white LED, chip-on-board package technology to achieve high colour rendering index and high luminous efficacy by optimising the spectral power distribution. The chip-on-board package light source can achieve a colour rendering index over 90 and a luminous efficacy over 90 lm/W while the power is 45W. It can be widely used in commercial lighting applications.

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