The characteristics of an LED need to be understood prior to the use. Please select a product suitable for your needs. CONTENTS 1. Introduction P.2 2. Absolute maximum rating P.2 3. Electro-optical characteristics P.3 4. Chromaticity coordinates P.4 5. Current dependency of total luminous flux P.4 6. Current dependency of chromaticity P.5 7. Heat dissipation characteristics P.5 8. Temperature dependency of total luminous flux P.6 9. Temperature dependency of chromaticity P.6 10. References P.6 No items shall be allowed to exceed the maximum rating when setting the conditions of use for an LED 1. Introduction Importance of understanding of characteristics It is very important to understand the characteristics of an LED prior to the use. Some characteristics are provided as an engineering document typified by specifications. In this document, the main characteristics of an LED are described based on the specifications of the CL-L251-C4N. As some characteristics described in this document is an example, please check the specifications for each product when actually using an LED. 2. Absolute maximum rating No items should be allowed to exceed limit values Table-1 shows the absolute maximum rating of the CL-L251-C4N. The absolute maximum rating means a limit value not to be exceeded. Even when several items are included, none of them should exceed limit values. In cases where these limit values are exceeded, an LED could have a shortened lifetime or break as a result of serious damage. When setting the use conditions for an LED, please establish margins to prevent the absolute maximum rating from being exceeded in any situation. ■Table-1 Absolute maximum rating Items Symbol Maximum rating Units Allowable power dissipation Pd 5.9 W Forward current IF 0.56 A Pulse forward current IFP 0.8 A Reverse current IR 1 mA Operating temperature range TOP -30~+85 °C Storage temperature range TST -40~+100 °C Junction temperature TjMax 120 °C *1 Pulse forward current: Duty 1/10, Pulse Width 10msec *2 During D.C. application: Tj=Tc+Rj-c.Pd During pulse application: Tj=Tc+Rj-c.Pw ( dissipation per pulse ) .duty *1 *2 Understanding of basic characteristics that influence LED performance and reliability is the basis for settings 3. Electro-optical characteristics The most basic critical characteristics Table-2 shows the electro-optical characteristics of the CL-L251-C4N. These are the most basic characteristics of an LED. Forward voltage ( Vf ) is a voltage value needed for lighting. As shown in Figure-1, Vf varies according to forward current ( If ). It should be noted that If varies significantly with minute change in Vf. Reverse current is current that flows by the application of voltage in the reverse direction. As an LED has polarity, little current flows in the reverse direction. Please be aware that an LED will be broken if used with incorrect polarity. Thermal resistance shows heat dissipation performance of an LED package. The lower this value becomes, the higher heat dissipation performance can be achieved because of better heat transfer. Total luminous flux is the total amount of light released from an LED and indicates brightness. This can be the most critical characteristic of an LED. Average color rendering index is an index to indicate whether the color of an object is reproduced faithfully when applying light to the object. The reference light value is Ra=100, which decreases with the distance from the reference light. Although this product has the average color rendering index of Ra=65, which is not a high value, this results from putting a priority on high luminous efficacy. CITIZEN ELECTRONICS’ product lineup also offers products with a higher color rendering property so that you can choose products depending on the intended use. Symbol Conditions MIN TYP ( Tc=25°C ) MAX Units Forward voltage VF IF=480mA 8.75 9.30 10.5 V Reverse current IR VR=15V - - 100 µA Thermal resistance RJ-C Junction-case - 6.0 - °C/W Total luminous flux φv IF=480mA 340 425 - Im Ra IF=480mA - 65 - - Items Average color rendering index ■Figure-1 Forward current and Forward voltage Tc=25°C 9.6 9.4 9.2 VF ( V ) ■Table-2 Electro-optical characteristics 9.0 8.8 8.6 8.4 8.2 0 100 200 300 If ( mA ) 400 500 600 Please chose a product from our lineup according to the desired chromaticity or light quantity 4. Chromaticity coordinates Chromaticity range that varies with product model Various chromaticity ranges are defined in accordance with the product models. Also, chromaticity ranges that differ depending on chromaticity are defined for the identical product models. Figure-2a shows the chromaticity range of the CL-L251-MC4N1-C ( High luminous efficacy type ). This chromaticity range complies with the N1 chromaticity range defined by the ENERGY STAR’s standard. On the other hand, Figure-2b shows the chromaticity range of the CL-L251-MC4N1-C with different chromaticity. This chromaticity range is defined within a range of the 3-step McAdam color ellipse that is narrower than the L1 chromaticity range ( dotted line area ) defined by the ENERGY STAR’s standard. CITIZEN ELECTRONICS offers some other color variations. For more details, please refer to the specifications or ‘Chromaticity Range’. 0.44 0.38 0.43 0.37 0.42 0.36 0.41 0.35 0.40 0.34 0.39 0.33 0.38 0.32 0.32 5. ■Figure-2b 3-step McAdam color ellipse 0.39 y y ■Figure-2a ENERGY STAR's standard 0.33 0.34 x 0.35 0.36 0.37 0.37 0.41 0.42 0.43 0.44 x 0.45 0.46 Current dependency of total luminous flux Forward current must be strictly controlled ■Figure-3 Forward current and Total luminous flux ratio Figure-3 shows the relation between If and total luminous flux ratio. As shown in the chart, light Tc=25°C 1.2 quantity produced by an LED varies with If. If must be 1.0 φV ( a.u ) strictly controlled to stabilize the performance of a lighting fixture. Also, it is recommended for LED control to adopt the constant current driving system as Vf varies with 0.8 0.6 0.4 temperature. For details, please refer to ‘Driving’. 0.2 The If value can be changed in response to required 0.0 light quantity unless it exceeds an allowable value. 0 100 200 300 If ( mA ) The allowable value changes with temperature. Details are included later in this document. 4 400 500 600 Luminous efficacy and chromaticity vary with temperature An efficient heat dissipation system is a critical factor 6. Current dependency of chromaticity Chromaticity that varies depending on forward current ■Figure-4 Forward current and Chromaticity coordinates Tc=25°C 0.020 0.015 Please be aware that chromaticity varies depending chromaticity variation of the CL-L251-C4N. This chart 0.010 Δx,Δy on If. Figure-4 shows the relation between If and 0.005 0.000 -0.005 means chromaticity shifts to +0.003 for x, +0.007 for -0.010 y at If=100mA when setting If=480mA as a reference -0.020 value. 7. Δx -0.015 Δy 0 100 200 300 If ( mA ) 400 500 600 Heat dissipation characteristic Heat dissipation is a mandatory requirement for use Heat has various harmful effects on an LED. As an 3 ) into the equation-1. LED itself produces heat during light emission, it is Tc = 120−( 6 ・ 0.56 ・ 9.3 ) especially important to establish a heat dissipation = 89°C system that efficiently disperses heat and decreases This means Tj=120°C when using an LED with the temperature of an LED. The representative example If=0.56A at Tc=89°C. includes heat dissipation with a heat sink. As the In the case of Tc≤89°C, the allowable current is simulation results of the heat dissipation system If=0.56A because it is limited by the absolute modeled on a CITIZEN ELECTRONICS lighting LED are maximum rating of If. described in ‘Thermal Management’, please refer to the On the other hand, the allowable current is limited by document for the design of a heat dissipation system. the absolute maximum rating of Tj in the range of Next, the effect of heat on the characteristics of an Tc>89°C. In this case, the equation-2 is used to LED is described below. Figure-5 shows the relation obtain the allowable current. The more the case between case temperature ( Tc ) and allowable values temperature increases, the smaller the allowable of If of the CL-L251-C4N. These allowable values are current becomes. set to prevent each parameter from exceeding the If = ( Tj−Tc ) / ( Rj−c ・ Vf ) = ( 120−Tc ) / ( 6 ・ 9.3 ) = 2.15−( 0.018 ・ Tc )…② absolute maximum rating. As shown below, the calculating formula for junction temperature ( Tj ) determines the relationship ■Figure-5 Case temperature and Forward current 600 equation of If and Tc. Tc = Tj−( Rj−c ・ Pd ) = Tj−( Rj−c ・ If ・ Vf )…① The following is obtained by entering If ( 0.56A ), TjMax ( 120°C ) shown in Table-1 Absolute maximum rating in page 2 and Vf at 0.56A ( 9.3V from Figure-1 in page 89°C 500 IF ( mA ) Tj = ( Rj−c ・ Pd ) + Tc 400 Equation-2 Absolute maximum rating of If 300 200 100 0 0 25 50 75 Tc ( °C ) 100 125 Luminous efficacy and chromaticity vary with temperature 8. Temperature dependency of total luminous flux Luminous efficacy decreases as the temperature rises An LED has the property of reducing its luminous ■Figure-6 Case temperature and Total luminous flux ratio efficacy as the temperature rises. Figure-6 shows the If=480mA 110% relationship between case temperature and the total 100% condition of If=480mA. Total luminous flux ( φv ) at Tc=100°C decreases to approximately 82% of that at Tc=25°C. To keep luminous efficacy of an LED high, φV ( a.u ) luminous flux ratio of the CL-L251-C4N under the fixed 90% 80% 70% heat should be dissipated using a heat sink or other methods so that case temperature becomes as low as 60% possible. Please consider that total luminous flux is 50% decreased by heat when designing an LED lighting 0.0 20.0 40.0 9. 60.0 80.0 100.0 120.0 Tc ( °C ) fixture. Temperature dependency of chromaticity Chromaticity also shifts with a change in temperature ■Figure-7 Case temperature and Chromaticity coordinates If=480mA 0.020 Please also note that an LED has the property of 0.015 shifting its chromaticity with a change in temperature. temperature and chromaticity variations of the CL-L251-C4N under the fixed condition of If=480mA. In this case, when Tc is increased to 100°C, chromaticity shifts to +0.001 for x, +0.005 for y compared to the coordinates for Tc=25°C. 0.010 Δx,Δy Figure-7 shows the relationship between case 0.005 0.000 -0.005 -0.010 Δx -0.015 Δy -0.020 0.0 20.0 40.0 60.0 Tc ( °C ) 10. 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