Two LED channels can have the same number of LEDs, the same series-parallel configuration, and the same specified supply voltage range. Does that mean they should operate at the same current?
Not necessarily.
In a custom 405nm + 450nm LED module developed by NKT for an OEM curing device, both channels ultimately used identical LED quantities and series-parallel arrangements. Yet their operating currents were different.
The reason was not simply the difference in wavelength. The 405nm channel used high-power UV LEDs, while the 450nm channel used lower-power blue LEDs. Each channel had to be evaluated according to the electrical characteristics of its selected components.
This distinction matters whenever an OEM product combines different LED types, power ratings, or color channels on one PCB.
Circuit Configuration and Operating Current Are Different Design Decisions
When designing a multi-channel LED module, two related questions need to be answered.
First: How should the LEDs be connected?
The series-parallel arrangement determines how the LEDs are grouped electrically. The number of LEDs in series affects the required string voltage, while the number of parallel branches affects how individual branch currents contribute to the total module current.
Second: What current is appropriate for each channel?
That depends on the selected LED's electrical ratings, the intended operating conditions, and the application's output requirements.
These decisions are connected, but they are not interchangeable.
For example, two channels may each contain three parallel branches with the same number of LEDs per branch. If the intended current in each branch differs between channels, their total channel currents will also differ.
The identical arrangement does not establish an identical operating point.
A Real OEM Project: 405nm UV and 450nm Blue LEDs
NKT encountered this situation while developing a dual-channel LED module for an OEM curing device.
The customer required two separately controlled channels:
405nm: High-power Luminus UV LEDs
450nm: Lower-power blue LEDs from another manufacturer
The channels were not intended to operate simultaneously.
At the beginning of the project, the customer had already proposed the LED quantities. However, those quantities could not be arranged into a practical series-parallel configuration under the specified electrical conditions.
NKT reviewed the LED specifications and recalculated the quantities to establish a workable module configuration.
The resulting design had several matching characteristics:
| Electrical design item | 405nm channel | 450nm channel |
|---|---|---|
| Specified supply voltage range | Same range | Same range |
| Total LED quantity | Same | Same |
| LEDs per series string | Same | Same |
| Number of parallel branches | Same | Same |
| LED power class | High power | Lower power |
| Intended operating current | Different | Different |
This is the central lesson from the project:
Matching the number and arrangement of LEDs does not mean the selected LEDs should operate at the same current.
The 405nm and 450nm LEDs belonged to different power classes and had different electrical operating requirements. Their currents therefore had to be considered separately, even though the circuit arrangements matched.
Why the Same Series-Parallel Arrangement Can Still Work
A series-parallel configuration and an LED's operating current answer different electrical questions.
The series count is evaluated against the forward-voltage characteristics of the selected LEDs and the permitted operating-voltage conditions. The parallel-branch count is part of establishing the required total LED quantity and current distribution.
Once a practical arrangement has been identified, the appropriate operating current must still be determined for the specific LEDs used in each channel.
An LED's forward voltage also changes with current and operating conditions. Therefore, the expected string voltage needs to be evaluated at the intended current—not treated as a fixed number independent of the operating point.
In the NKT project, the selected 405nm and 450nm LEDs could be arranged using the same series and parallel counts while operating at different currents.
That does not mean their actual forward voltages were identical, or that their final power-supply and current-control arrangements were the same.
It means the module configuration could satisfy the specified design requirements without forcing both LED types to operate at one common current.
For a closer look at how LED forward voltage affects series count and voltage compatibility, see how LED forward voltage affects LED module circuit design.
Electrical Design Is Not the Same as Application Validation
For this curing project, NKT's work included reviewing the LED specifications, recalculating the LED quantities, establishing the electrical configuration, and developing the PCB layout.
NKT has optical power measurement equipment. However, application-level optical power testing was not performed for this project because the customer's actual operating conditions were not available.
Final performance validation was carried out by the customer in the curing equipment.
The customer's final power-supply arrangement was not confirmed. Although both channels were designed around the same specified voltage range, that alone does not establish whether the finished equipment used one power supply or separate supplies.
For an OEM project, it is important to distinguish the electrical parameters established during module development from the performance that must be verified in the finished machine.
The Same Principle Applies to Constant-Voltage RGBW Modules
A different example comes from NKT's constant-voltage RGB and RGBW module development.
In an RGBW LED package, red, green, blue, and white light-emitting chips are integrated into one component. The individual color channels can be controlled separately.
All four channels may be designed for the same nominal supply voltage, but their forward-voltage characteristics and operating-current requirements are not necessarily identical.
For these modules, NKT engineers calculate and select current-limiting resistors for the individual color channels using the LED datasheet and the customer's electrical requirements.
The calculations consider the supply voltage, channel forward voltage, intended current, circuit arrangement, and resistor power dissipation.
The design method is different from the 405nm/450nm curing project: current-limiting resistors are part of the constant-voltage RGBW circuit, while the curing equipment's final external current-control arrangement was not confirmed.
Nevertheless, the underlying principle is consistent:
A shared supply-voltage requirement does not remove the need to evaluate each LED channel individually.
What OEM Engineers Should Confirm Before PCB Layout
In many custom LED module projects, the customer already knows the available PCB space, preferred LEDs, required wavelengths, or voltage limitations.
Sometimes the LED quantity has also been specified.
But those inputs do not automatically establish a practical electrical design.
Before finalizing the PCB, it is useful to clarify:
LED selection: Which LED models or power classes are required for each channel?
Electrical conditions: What supply-voltage range and operating-current requirements apply?
Channel operation: Will channels operate independently, simultaneously, or in different combinations?
Output requirements: What optical output or application performance is expected from each channel?
Mechanical constraints: What PCB dimensions, mounting holes, and component positions must be maintained?
If the final power supply has not been selected, the available system requirements can still provide a starting point for evaluating the module configuration.
NKT can review the selected LEDs and electrical constraints, then propose an LED quantity and circuit arrangement for the OEM application.
This work is part of our custom OEM LED module development services.
When a Customer-Specified LED Count Needs a Second Look
The 405nm/450nm project began with LED quantities already proposed by the customer.
The challenge was not simply fitting those LEDs onto the PCB. The quantities also had to work electrically with the selected components and the specified voltage conditions.
After reviewing the requirements, NKT revised the quantities and established a workable arrangement. Both channels ended up with matching LED counts and circuit structures, but different operating currents.
For OEM engineers, the practical takeaway is straightforward: LED quantity, series-parallel configuration, and operating current should be evaluated together—but they should not be assumed to be the same design decision.
If your project combines different LED types or power ratings, you can send NKT the preferred LED part numbers, available PCB dimensions, voltage requirements, and intended output targets. We can review the electrical configuration before the design moves further into PCB development.
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