LTL42FKGD Through Hole LED Lamp Datasheet - 5mm Diameter - 2.6V Forward Voltage - Green Color - 81mW Power - English Technical Document

1. Product Overview

The LTL42FKGD is a through-hole mounted LED lamp designed for status indication and illumination in a wide range of electronic applications. It features a 5mm diameter package with a green diffused lens, providing a wide viewing angle and uniform light distribution. The device utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for its emitter, which is known for high efficiency and good color purity in the green spectrum. This LED is constructed to be lead-free and fully compliant with RoHS (Restriction of Hazardous Substances) directives, making it suitable for modern electronic manufacturing requirements.

1.1 Core Advantages

• High Luminous Output: Delivers typical luminous intensity of 240 mcd at a standard drive current of 20mA, ensuring bright and clear visibility.
• Energy Efficiency: Features low power consumption with a typical forward voltage of 2.6V, contributing to overall system energy savings.
• Design Flexibility: Available in a standard 5mm through-hole package, allowing for versatile mounting on printed circuit boards (PCBs) or panels. The wide 60-degree viewing angle ensures good visibility from various angles.
• Compatibility: The low current requirement makes it compatible with integrated circuit (IC) outputs without the need for complex driver circuits in many applications.
• Reliability: Designed for an operating temperature range of -40°C to +85°C, suitable for use in diverse environmental conditions.

1.2 Target Applications

This LED is engineered for broad applicability across multiple industries. Its primary function is status indication, but its brightness also allows for limited area illumination. Key application sectors include:

• Communication Equipment: Indicator lights for power, network activity, and system status on routers, switches, and modems.
• Computer Peripherals: Power and activity indicators on desktop computers, laptops, external drives, and keyboards.
• Consumer Electronics: Status lights on audio/video equipment, home appliances, toys, and portable devices.
• Home Appliances: Operational indicators on washing machines, microwaves, ovens, and other white goods.
• Industrial Controls: Panel indicators for machinery, control systems, test equipment, and instrumentation.

2. In-Depth Technical Parameter Analysis

The following section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters specified for the LTL42FKGD LED. Understanding these parameters is crucial for proper circuit design and reliable operation.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended and will adversely affect reliability.

• Power Dissipation (Pd): 81 mW maximum. This is the total power (Forward Voltage * Forward Current) that can be safely dissipated as heat by the LED package at an ambient temperature (TA) of 25°C.
• DC Forward Current (IF): 30 mA maximum continuous current. Exceeding this value will generate excessive heat, leading to accelerated lumen depreciation and potential catastrophic failure.
• Peak Forward Current: 60 mA maximum, but only under pulsed conditions with a duty cycle of 10% or less and a pulse width of 10 microseconds or less. This rating is relevant for brief, high-intensity flashes.
• Derating: The maximum allowable DC forward current must be linearly reduced by 0.57 mA for every degree Celsius the ambient temperature rises above 50°C. This is a critical design consideration for high-temperature environments.
• Operating & Storage Temperature: The device can function from -40°C to +85°C and can be stored from -40°C to +100°C.
• Lead Soldering Temperature: 260°C for a maximum of 5 seconds, measured 2.0mm (0.079 inches) from the LED body. This defines the process window for hand or wave soldering.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured under standard test conditions (TA=25°C). Designers should use the typical or maximum values as appropriate for their design margins.

• Luminous Intensity (Iv): Ranges from a minimum of 85 mcd to a maximum of 400 mcd at IF=20mA, with a typical value of 240 mcd. The actual value for a specific unit is determined by its bin code (see Section 4). The measurement uses a sensor filtered to match the photopic (human eye) response curve (CIE). A ±15% testing tolerance is applied to the bin limits.
• Viewing Angle (2θ1/2): 60 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on the central axis (0 degrees). A 60-degree angle provides a good balance between focused brightness and wide visibility.
• Peak Emission Wavelength (λP): 574 nm. This is the wavelength at which the spectral power distribution of the emitted light is at its maximum.
• Dominant Wavelength (λd): Ranges from 563 nm to 573 nm, defining the perceived green color of the LED. It is derived from the CIE chromaticity coordinates and represents the single wavelength that best matches the LED's color.
• Spectral Line Half-Width (Δλ): 20 nm. This indicates the spectral purity; a smaller value means a more monochromatic (pure color) light. A 20nm width is typical for AlInGaP green LEDs.
• Forward Voltage (VF): 2.6V typical at IF=20mA, with a maximum of 2.6V. The minimum is 2.1V. This parameter has a distribution; designers must account for the maximum VF when calculating series resistor values to ensure adequate current limiting.
• Reverse Current (IR): 100 μA maximum when a reverse voltage (VR) of 5V is applied. Important Note: This LED is not designed for reverse-bias operation. This test condition is for characterization only. Applying a continuous reverse voltage can damage the device.

3. Binning System Specification

To ensure consistency in brightness and color for production applications, LEDs are sorted into performance bins. The LTL42FKGD uses a two-dimensional binning system.

3.1 Luminous Intensity Binning

Units are sorted based on their measured luminous intensity at 20mA. The bin code is marked on the packaging.

• Bin EF: 85 mcd (Min) to 140 mcd (Max)
• Bin GH: 140 mcd (Min) to 240 mcd (Max)
• Bin JK: 240 mcd (Min) to 400 mcd (Max)

Tolerance on each bin limit is ±15%.

3.2 Dominant Wavelength Binning

Units are also sorted by their dominant wavelength, which correlates directly with the shade of green.

• Bin H05: 563.0 nm (Min) to 566.0 nm (Max)
• Bin H06: 566.0 nm (Min) to 568.0 nm (Max)
• Bin H07: 568.0 nm (Min) to 570.0 nm (Max)
• Bin H08: 570.0 nm (Min) to 573.0 nm (Max)

Tolerance on each bin limit is ±1 nm.

A complete product order will be specified with both an intensity bin code (e.g., GH) and a wavelength bin code (e.g., H07) to guarantee both brightness and color consistency within the lot.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, the typical relationships between key parameters are described below. These curves are essential for understanding device behavior under non-standard conditions.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The LED exhibits a non-linear I-V characteristic typical of a diode. The forward voltage (VF) has a positive temperature coefficient, meaning it decreases slightly as the junction temperature increases for a given current. The curve shows the threshold voltage (where current begins to flow significantly) is around 1.8V to 2.0V for AlInGaP green LEDs, rising to the typical 2.6V at 20mA.

4.2 Luminous Intensity vs. Forward Current

The light output (luminous intensity) is approximately proportional to the forward current in the normal operating range (e.g., up to 30mA). However, efficiency (lumens per watt) may peak at a current lower than the maximum rating. Driving the LED at higher currents increases output but also generates more heat, which can reduce efficiency and long-term reliability.

4.3 Luminous Intensity vs. Ambient Temperature

The light output of an LED decreases as the junction temperature rises. While the AlInGaP material is more temperature-stable than some other LED types, a derating in output is expected as the ambient temperature approaches the maximum operating limit. This is why thermal management (e.g., not exceeding current ratings) is important for maintaining consistent brightness.

4.4 Spectral Distribution

The spectral output curve centers around the peak wavelength of 574 nm with a characteristic half-width of 20 nm. The dominant wavelength (λd), which defines the color point, is calculated from this spectrum. The curve is generally Gaussian in shape.

5. Mechanical & Package Information

5.1 Outline Dimensions

The LED conforms to the standard 5mm round through-hole package dimensions. Key mechanical specifications include:

• Lead diameter: Standard 0.6mm.
• Lead spacing: 2.54mm (0.1 inch) nominal, measured where leads emerge from the package body.
• Body diameter: 5.0mm nominal.
• Total height: Approximately 8.6mm from the bottom of the leads to the top of the dome lens, though this can vary slightly.
• Tolerance: ±0.25mm on most linear dimensions unless otherwise specified.
• Protruded resin under the flange is a maximum of 1.0mm. This is important for PCB layout to ensure the LED sits flush on the board.

5.2 Polarity Identification

The LED has two axial leads. The longer lead is the anode (positive, A+), and the shorter lead is the cathode (negative, K-). Additionally, the cathode side of the LED flange (the flat rim at the base of the lens) often has a small flat spot or notch. Always verify polarity before soldering to prevent reverse connection, which can damage the device.

6. Soldering & Assembly Guidelines

Proper handling and soldering are critical to prevent mechanical or thermal damage to the LED.

6.1 Storage Conditions

For long-term storage, keep LEDs in their original moisture-barrier packaging. The recommended storage ambient is ≤30°C and ≤70% relative humidity. If removed from the original packaging, use the LEDs within three months. For extended storage outside the original bag, store them in a sealed container with desiccant or in a nitrogen-purged desiccator to prevent moisture absorption, which can cause \"popcorning\" during soldering.

6.2 Lead Forming

If leads need to be bent for mounting, this must be done before soldering and at room temperature. Bend the leads at a point at least 3mm away from the base of the LED lens. Do not use the LED body or the lead frame as a fulcrum. Apply the minimum force necessary to avoid stressing the internal wire bonds.

6.3 Cleaning

If cleaning is required after soldering, use only alcohol-based solvents such as isopropyl alcohol (IPA). Avoid aggressive or ultrasonic cleaning that could damage the epoxy lens or internal structure.

6.4 Soldering Process Parameters

Hand Soldering (Iron):

• Maximum Iron Temperature: 350°C
• Maximum Soldering Time: 3 seconds per lead
• Minimum Distance from Lens Base: 2.0mm. The solder joint must not wick up the lead closer than this to the plastic body.
• Do not immerse the lens in solder.

Wave Soldering:

• Maximum Pre-heat Temperature: 100°C
• Maximum Pre-heat Time: 60 seconds
• Maximum Solder Wave Temperature: 260°C
• Maximum Contact Time: 5 seconds
• Minimum Dipping Position: No lower than 2mm from the base of the epoxy lens.

Critical Note: Infrared (IR) reflow soldering is not suitable for this through-hole LED product. The epoxy lens cannot withstand the high temperatures of a reflow oven profile. Excessive soldering temperature or time can cause lens deformation, cracking, or internal failure.

7. Packaging & Ordering Information

7.1 Packaging Specification

The LEDs are packaged in anti-static bags to prevent ESD damage. The standard packing hierarchy is:

1. Packing Bag: Contains 1000, 500, 200, or 100 pieces. The bag is labeled with the part number, quantity, and bin codes (Intensity and Wavelength).
2. Inner Carton: Contains 10 packing bags. The total quantity per inner carton is typically 10,000 pieces (when using 1000-piece bags).
3. Master/Outer Carton: Contains 8 inner cartons. The total quantity per master carton is typically 80,000 pieces.

For shipping lots, only the final pack may contain a non-full quantity.

8. Application Design Recommendations

8.1 Drive Circuit Design

An LED is a current-driven device. Its brightness is controlled by the forward current (IF), not the voltage. The most critical design element is the current-limiting resistor.

Recommended Circuit (Circuit A): Use a series resistor for each LED. The resistor value (R) is calculated using Ohm's Law: R = (Vsupply - VF_LED) / IF. Use the maximum VF from the datasheet (2.6V) for a conservative design that ensures the current never exceeds the desired IF even with LED-to-LED variation.

Example: For a 5V supply and a target IF of 20mA: R = (5V - 2.6V) / 0.020A = 120 Ohms. The nearest standard value (e.g., 120Ω or 150Ω) would be chosen, and its power rating must be sufficient (P = I²R).

Circuit to Avoid (Circuit B): Do not connect multiple LEDs directly in parallel from a single current-limiting resistor. Small variations in the forward voltage (VF) characteristic between individual LEDs will cause severe current imbalance. One LED with a slightly lower VF will draw disproportionately more current, leading to uneven brightness and potential overstress of that LED.

8.2 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge. Standard ESD precautions must be followed during handling and assembly:

• Operators should wear grounded wrist straps or anti-static gloves.
• All workstations, tools, and equipment must be properly grounded.
• Use conductive or dissipative mats on work surfaces.
• Store and transport LEDs in ESD-protective packaging.
• Consider using an ionizer to neutralize static charges that may accumulate on the plastic lens during handling.

8.3 Thermal Considerations

While this is a low-power device, thermal management is still important for longevity. Do not exceed the absolute maximum ratings for power dissipation and forward current. Adhere to the derating curve above 50°C ambient. Ensure adequate spacing between LEDs on a PCB to allow for heat dissipation and avoid creating local hot spots.

9. Technical Comparison & Differentiation

The LTL42FKGD, as a standard 5mm AlInGaP green LED, occupies a well-established position in the market. Its key differentiators are defined by its specific performance bins.

• vs. Lower-Brightness Green LEDs: Units binned in the JK range (240-400 mcd) offer significantly higher luminous intensity than generic \"standard brightness\" green LEDs, making them suitable for applications requiring high visibility or used behind lightly tinted lenses/diffusers.
• vs. Other Green Technologies: Compared to older Gallium Phosphide (GaP) green LEDs, AlInGaP technology provides higher efficiency and a more saturated, \"true\" green color (dominant wavelength in the 560-570nm range vs. 555nm for GaP).
• vs. Blue/Yellow-Based \"Green\" LEDs: Some white or green LEDs use a blue chip with a yellow phosphor, which can have a different spectral quality (broader spectrum) and potentially lower color purity than a direct-emitting AlInGaP green LED.
• Primary Advantage: Its main advantage is a combination of proven reliability, ease of use (through-hole), good efficiency, and the availability of tight brightness and color binning for consistent appearance in production runs.

10. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive this LED directly from a 3.3V or 5V microcontroller pin?
A: No, not directly. While the forward voltage (~2.6V) is less than these supply voltages, an LED must be current-limited. Connecting it directly would attempt to draw excessive current, potentially damaging both the LED and the microcontroller pin. Always use a series resistor as described in Section 8.1.

Q2: What resistor value should I use for a 12V supply?
A: Using the formula R = (12V - 2.6V) / 0.020A = 470 Ohms. The power dissipated in the resistor is P = (0.020A)² * 470Ω = 0.188W, so a standard 1/4W (0.25W) resistor is sufficient. A 470Ω or 560Ω resistor would be appropriate.

Q3: Why is there a minimum forward voltage (2.1V) listed?
A: The forward voltage has a distribution across production units due to slight variations in the semiconductor material and manufacturing process. The 2.1V minimum is the lower end of this distribution. Designing with the typical or maximum value ensures the circuit works correctly for all units.

Q4: Can I use this LED outdoors?
A: The datasheet states it is good for indoor and outdoor signs. The operating temperature range (-40°C to +85°C) supports outdoor use. However, for prolonged direct weather exposure, consider additional protection (conformal coating on the PCB, a sealed enclosure) as the epoxy lens may degrade from prolonged UV exposure or moisture ingress over many years.

Q5: How do I interpret the bin codes when ordering?
A: You must specify both an Intensity Bin (e.g., GH) and a Wavelength Bin (e.g., H07) to get a consistent batch. If you do not specify, you may receive a mix, leading to visible brightness and color differences in your product. For most applications, specifying the middle bins (GH for intensity, H06/H07 for wavelength) is a good practice.

11. Practical Application Examples

Example 1: Multi-Channel Status Indicator Panel
In an industrial control box, ten LTL42FKGD LEDs (binned GH/H07) are used on a front panel to indicate the status of ten different sensors or machine states. Each LED is driven by a separate output of a 5V logic buffer IC (e.g., 74HC244). A single 120Ω resistor is placed in series with each LED. The consistent binning ensures all ten lights have a uniform green color and very similar brightness, providing a professional appearance. The wide 60-degree viewing angle allows the status to be seen from various operator positions.

Example 2: Backlighting for a Membrane Switch
A single LTL42FKGD LED (binned JK for higher brightness) is placed behind a translucent icon on a membrane keypad. It is driven by a microcontroller GPIO pin through a 150Ω resistor from a 3.3V supply. The diffused lens of the LED helps create an even illumination under the icon. The low current requirement (~13mA calculated: (3.3V-2.6V)/150Ω) is well within the GPIO pin's capability, simplifying the design.

12. Operating Principle

The LTL42FKGD is a semiconductor light source based on a p-n junction formed from AlInGaP (Aluminum Indium Gallium Phosphide) materials. When a forward voltage exceeding the diode's threshold is applied, electrons from the n-type region and holes from the p-type region are injected into the active region (the junction). When these charge carriers (electrons and holes) recombine, they release energy in the form of photons (light particles). The specific composition of the AlInGaP alloy determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted photons—in this case, green light with a dominant wavelength around 570 nm. The epoxy lens serves to protect the semiconductor chip, shape the light output beam (creating the 60-degree viewing angle), and diffuse the light to soften its appearance.

13. Technology Trends

Through-hole LEDs like the LTL42FKGD represent a mature and highly reliable technology. The general trend in the LED industry is towards surface-mount device (SMD) packages (e.g., 0603, 0805, 3528) for most new designs due to their smaller size, suitability for automated pick-and-place assembly, and lower profile. However, through-hole LEDs maintain significant relevance in several areas: for prototyping and hobbyist use due to ease of hand-soldering; in applications requiring very high reliability and robust mechanical connection (vibration-resistant); for panel mounting where the leads can be secured directly to a chassis; and in educational settings. The technology itself continues to see incremental improvements in efficiency (more light output per watt) and color consistency through advanced epitaxial growth and binning processes, even within established package formats like the 5mm lamp.