This text is a solution to a number of widespread technical issues within the LED show trade by Zhao Yun, senior utility engineer of OSRAM Opto Semiconductors, and Liang Zechun, advertising supervisor, and OSRAM Opto Semiconductors’ corresponding product options for various technical facets
The upper the brightness of the out of doors show, the higher
Within the home LED show trade, brightness has all the time been an important indicator for everybody to judge the show impact, particularly for out of doors screens. Over time, it has shaped a misunderstanding that the upper the brightness, the higher, however it ignores one other indicator that’s extraordinarily essential to the show effect-contrast
In accordance with the definition of trade normal SJ/T11281-2007 “Gentle Emitting Diode (LED) Show Display screen Check Methodology”, underneath a sure ambient illumination, the ratio of the utmost brightness of the show display to the background brightness is named the best distinction ratio (for particular take a look at situations and strategies see the usual). For instance, the brightness of a display is 5000cd/m2 in full white state, and 1cd/m2 in full black state, so the distinction ratio of the display is 4999:1. The definition of distinction really emphasizes the diploma of recognizability of the show display within the use surroundings. In contrast with the brightness index, the distinction index will increase the brightness of the complete black display state, and the brightness of the complete black display state is said to the ambient gentle and the display physique ( The reflective properties of LEDs and masks) are carefully associated. The next out of doors comparability examples present {that a} display with excessive brightness and low distinction shouldn’t be as efficient as a display with comparatively low brightness and excessive distinction
Determine 1 Comparability of the results of screens with totally different brightness and distinction ratio
With a purpose to enhance the distinction of LED shows, OSRAM Opto Semiconductors has been specializing in lowering the reflectance of LED shows because it launched the world’s first black-body surface-mounted three-in-one LED (LRTB GFUG) in 2007. The present most important product LRTB GRUG (Fig. 2) It is among the LEDs with the best floor blackness available on the market. Not solely does it use a black physique shell, however the bracket across the chip can be handled with black physique. With the particular driver and masks design, this product can obtain the best distinction ratio as much as 8000:1. Determine 2 LRTB GRUG of Osram Opto Semiconductors product
As well as, even underneath sure situations of distinction, the upper the brightness, the higher. A display with an excessive amount of brightness could trigger the next three issues: (1) excessive power consumption; (2) gentle air pollution; (3) diminished {hardware} life
To sum up, we consider that the brightness of the LED show shouldn’t be as excessive as attainable, and the distinction index can mirror the standard of the show impact higher than the peak index; and underneath the situation of a sure distinction, the upper the brightness, the higher
The bigger the viewing angle of the led show, the higher
Earlier than discussing the scale of the viewing angle, we additionally have to make clear the idea of the viewing angle. Many producers within the trade don’t set the viewing angle specs precisely sufficient, pondering that the angles from which the displayed content material may be seen are all viewing angles, however this isn’t the case. In accordance with the definition of the trade normal SJ/T 11281-2007 “Gentle Emitting Diode (LED) Show Display screen Check Methodology”, assuming that the brightness of the conventional route of the show display is Lf, the brightness of the show display is detected from the left and proper sides of the conventional line of the show display heart, when When the luminance values on the left and proper sides drop to Lf/2, the angle shaped between the 2 statement strains is named the viewing angle within the horizontal route of the show display. The identical is true for vertical viewing angles
The viewing angle of the LED itself can be primarily based on the identical definition above. Because of the definition of the brightness take a look at on the show, the sunshine probe wants to interchange a minimum of 16 LED pixels, which can trigger the viewing angle of the display to be barely bigger than that of the LEDs used (assuming that the masks has no gentle blocking). As proven in Determine 3, the LED show manufactured from 100-degree viewing angle LEDs has a viewing angle of 134 levels
Determine 3 Relative gentle depth comparability between LED and LED displa
So is the viewing angle of the LED show larger the higher? In truth, it is dependent upon totally different utility necessities. For instance, the highway site visitors info display, as a result of the viewers of the displayed content material is just highway automobiles, so the viewing angle normally solely must be about 30 levels. Extreme viewing angles will trigger gentle air pollution at different angles and cut back power effectivity; one other instance is the outside wall of an out of doors constructing. Promoting show screens are supposed for passers-by on the road, so the horizontal viewing angle must be comparatively massive, whereas the vertical viewing angle must be minimized
For various utility wants, OSRAM Opto Semiconductors has a collection of LED merchandise with totally different viewing angle specs, and three of them are listed in Determine 4
Determine 4 Show utility LEDs with totally different viewing angle specification
The narrower the LED wavelength vary, the extra constant the colour have to be
The uniformity of the colour displayed by the led show is dependent upon the next three factors: (1) the consistency of the colour between the person LEDs, (2) the consistency of the output present of the motive force chip, and (3) the consistency of the temperature. Amongst them, the consistency between LED people is an important. Though the present point-by-point correction methodology primarily based on the management system may be very mature, the correction is at the price of sacrificing absolutely the brightness and the saturation of the three main colours. Due to this fact, the manufacturing facility consistency of the LED remains to be essential to the uniformity of the displayed coloration
The present mainstream follow within the trade is that LED suppliers use the dominant wavelength for coloration binning, and constantly slim the higher and decrease limits of the dominant wavelength to enhance coloration consistency. Nevertheless, utilizing the dominant wavelength as the one parameter limiting coloration is a very unreasonable method
Determine 5 reveals the CIE1931 coloration house outlined within the discipline of colorimetry. All seen gentle colours are positioned inside the horseshoe form and may be strictly outlined by (x, y) coordinates. Every coloration has two properties of dominant wavelength and saturation. The dominant wavelength is outlined by the wavelength level on the boundary and the road earlier than the purpose of equal power (0.333, 0.333), and the saturation is outlined by the ratio on this line phase. For instance, in Determine 5, we choose a sure inexperienced level B, make a straight line connecting level E and level B and prolong it to the boundary level A (540nm), then the dominant wavelength of the inexperienced coloration is 540nm; and the saturation of this level is BE /AE = 50%. All the colour factors on the road phase AE have a dominant wavelength of 540nm, and the distinction is that the saturation shouldn’t be the identical
Determine 5 CIE1931 coloration spac
Due to this fact, the colour binning methodology of the dominant wavelength shouldn’t be scientific. Because of the full lack of saturation specification limits, even the narrowest wavelength vary can’t exactly restrict the colour consistency
For all LED show merchandise, OSRAM Opto Semiconductors adopts the colour coordinate bin methodology primarily based on the CIE1931 coloration house, and concurrently limits the specs of the dominant wavelength and saturation of the LEDs shipped. The intuitive comparability with different producers’ most important wavelength bins is proven in Determine 6. The yellow quadrilateral within the determine is the colour space of the No. 5 bin of OSRAM LED LRTB GRUG inexperienced gentle (for extra different bin areas, please confer with the product specification). And assuming that one other LED provider takes the dominant wavelength vary of 526nm to 531nm because the transport specification, then the colour vary akin to this specification in Determine 6 is the pink triangle space, which is nearly 5 instances the scale of the yellow quadrilateral. Even when the dominant wavelength vary is narrowed right down to 2nm width from 527nm to 529nm, the colour discrete area remains to be twice the scale of our coloration index quadrilatera
Determine 6 Comparability of the colour coordinate bin of OSRAM Opto Semiconductors and the principle wavelength bin of different manufacture
To sum up, because of the irrationality of defining the colour itself by the dominant wavelength, the colour consistency can’t be successfully improved by narrowing the dominant wavelength vary of LEDs. The right strategy is to moderately restrict the dominant wavelength vary and saturation vary of the shipped merchandise on the similar time via the colour coordinate bin methodology. Osram Opto Semiconductors adopts the colour coordinate binning methodology for all LED show merchandise. Via correct on-line binning tools and materials course of precision management, we cannot solely guarantee our personal excessive sufficient manufacturing fee but additionally present LED show purposes with LEDs with excessive coloration consistenc
The upper the show pixel density, the bette
Show pixel density all the time appears to be the larger the higher, as a result of it signifies that in idea the show display can be finer. Nevertheless, how huge the pixel density is, we predict it must be thought of from the next three facet
First, the decision means of the human eye (statement tools apart from the human eye shouldn’t be thought of in the meanwhile. In accordance with the necessities of “TCO Licensed Shows 7.0”, a minimum of 30 show pixels are required inside a 1-degree viewing angle of the human eye, which signifies that a single pixel pitch For the viewing angle requirement is 1/
The restrict to which the human eye can distinguish two level gentle sources is that the 2 level gentle sources and the human eye type an arc angle of 1/60, then the space between the 2 factors (Dpp) and the statement distance (L) have the next relationshi
When the statement distance (L) is 10 meters, the restrict of level spacing (Dpp) is 5.8mm. A better pixel density could be pointles
Determine 7 Level spacing and statement distan
Second, the load capability of movie supply, video processor and driver chip. If the decision of the movie supply is way decrease than that of the show machine, the show machine is clearly overcapacitated. For video processors and driver chips, if the capabilities stay fixed, the rise in load pixels will end in a lower in refresh fee or grey scale. In lots of circumstances, the show impact introduced by low refresh or low grey is worse than low pixel densit
Third, price. To begin with, the rise within the variety of LEDs will enhance with the sq. of the pixel decision. The price of the PCB board will even enhance as a result of extra accountable circuit design per unit space. As well as, if you happen to do not need to sacrifice line scan, refresh fee or grey scale, the price of driving elements will enhance dramaticall
Below the identical dot pitch, the bigger the LED dimension, the bette
This query may be equal to the proportion of the LED light-emitting floor within the whole show space, whether or not the show impact is larger or higher. The primary level that must be emphasised is that to debate the show impact, it’s essential to be at an acceptable viewing distance. If the statement distance is simply too brief, leading to discrete sample pixels, it’s a downside of inappropriate pixel density design, fairly than an issue of inadequate proportion of LED
When the viewing distance is large led video wall sufficient, the proportion of the LED light-emitting floor within the whole show space will have an effect on the distinction of the display. Because the house between the LED and the LED can be occupied by the masks, and even the blackest LED, the reflectance fee can be larger than that of the masks, so the upper the proportion of the LED light-emitting floor within the whole show space, the upper the distinction of the display. decrease. Determine 8 is a schematic comparability of shows with the identical dot pitch and totally different LED dimension
Determine 8 Schematic comparability of shows with the identical dot pitch and totally different LED siz
In response to this idea, OSRAM Opto Semiconductors has launched a high-brightness LED (mannequin LRTB R48G) in a 1010-size bundle, which is appropriate for show designs with a dot pitch of 3-5mm. In contrast with conventional designs primarily based on 2020 or related dimension LEDs, LRTB R48G can present larger show distinction whereas guaranteeing brightnes
Outside safety means = waterproof performanc
LED shows for out of doors use want to deal with harsh environmental exams, and the reliability necessities of LEDs are superb. At current, many practices within the trade straight have a look at the waterproof efficiency. It’s true that the failure of LEDs on shows as a result of moisture or water ingress accounts for a excessive proportion of all the varied failure modes. Nevertheless, out of doors reliability of LEDs is in no way merely equal to waterproof efficiency. We consider that along with the necessities for waterproof efficiency of LEDs, a minimum of the next three factors have to be thought of: (1) the affect of outside complicated fuel elements on LEDs; (2) the affect of photo voltaic radiation on LEDs; (3) extra extreme out of doors excessive and low temperature and the impact of humidity with LED
OSRAM Opto Semiconductors strictly stipulates the next 7 classes and 22 reliability take a look at necessities for LEDs utilized in out of doors LED shows. By way of waterproof efficiency, the worldwide basic IP degree take a look at specification is adopted. For the opposite three factors talked about above, we add corrosive fuel take a look at and salt spray take a look at to make sure that the product is utilized in varied harsh out of doors environments (equivalent to industrial or car exhaust surroundings, humid seaside surroundings, and so on.); photo voltaic/ultraviolet radiation take a look at can guarantee The efficiency reliability of the product underneath direct daylight open air; extra complete excessive and low temperature life exams with humidity, and excessive and low temperature affect exams to cope with drastic modifications in out of doors temperature and humidity. For particular take a look at situations and outcomes, please confer with the reliability report paperwork of various merchandise of OSRAM Opto Semiconductor
Determine 9 Osram Opto Semiconductors’ take a look at specs for LED merchandise utilized in out of doors show scre
s
Doesn’t “useless gentle” imply that the LED has not fail
?
The trade normally makes use of “useless gentle” (LED brief circuit or open circuit) to outline the failure of an LED, and makes use of the “useless gentle” fee ppm to guage the standard of an LED. It’s true that the brief circuit and open circuit of the LED will straight result in the failure of the useless pixels, linear or cross show on the LED show. Nevertheless, in our opinion, failure of an LED can’t be outlined as simply an open or brief circuit, however must be a change in any key specification past a suitable vary. Such specification parameters ought to a minimum of embrace: (1) Brightness – the attenuation of LED brightness will cut back the brightness of the display, the inconsistent attenuation between RGB will trigger the general coloration drift of the display, and the inconsistent attenuation between particular person LEDs will trigger “flower display”; ( 2) Coloration level – the change of coloration level will trigger the lower of display saturation, the colour drift of the three main colours and white stability, and the inconsistent coloration level offset between LED people will trigger “flower display”; (3) Voltage worth – – The getting older of LED will trigger the voltage worth to extend, and too excessive LED voltage could trigger issues within the management of the motive force chip; (4) Reverse leakage present – particularly for indoor small-pitch purposes, the rise in reverse leakage present is exactly Signs of LED brief circu
.
OSRAM Opto Semiconductors can present detailed reliability take a look at studies for all LED merchandise utilized in LED shows. The content material of the report shouldn’t be solely to supply the “useless gentle” fee, but additionally via the curve of key LED specs altering with time in every take a look at (as proven in Determine 10, the product LRTB GRUG within the excessive temperature and excessive humidity 1000-hour take a look at, brightness, voltage and coloration level change curves with time).
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