Open the product page of any LED and you will see a row of columns: forward current, forward voltage, luminous intensity, dominant wavelength, viewing angle, lens, and so on. Every cell is a number, but which ones affect your circuit, and which ones affect how the product looks? This article uses real product specifications from our website as examples and walks through the LED specification table column by column, ending with a part selection checklist. It helps to keep one of our product pages open as you read.
Table of Contents
In Short: 4 Things to Check First in an LED Specification Table
- Forward current (IF): the luminous intensity and voltage in the table were measured at this current. Most OPTO PLUS standard LEDs are specified at 20mA.
- Forward voltage (VF): decides whether your supply voltage is high enough and how to calculate the current-limiting resistor. Red, yellow and orange are a little over 2V; blue, green and white are a little over 3V.
- Luminous intensity (mcd): must be read together with the viewing angle and lens. Do not compare the numbers alone.
- Dominant wavelength or chromaticity coordinates: define the color. For single-color LEDs, check the dominant wavelength (nm); for white LEDs, check the chromaticity coordinates or color temperature.
What Columns Does an LED Specification Table Have?
LEDs in different packages do not list exactly the same columns on their product pages. Take two series from our website as examples:
| Product | Specification table columns |
|---|---|
| Side-view PLCC LED (OPS-L0828 series) | Part number, documents, forward current, color, forward voltage, luminous intensity, dominant wavelength / chromaticity coordinates |
| 3mm through-hole LED lamp (OPL-3014 series) | All of the above, plus LED lens and viewing angle |
The light from a through-hole lamp exits through the lens at the top of the package, so its table adds lens and viewing angle columns. The “documents” column is the datasheet. Anything not listed in the product page table, such as the absolute maximum current, has to be looked up in the datasheet.
Forward Current: The Numbers in the Table Were Measured at This Current
Forward current is the test condition for the luminous intensity and forward voltage in the same row. Most of our standard LEDs are specified at 20mA. For example, in the OPS-L0828 side-view PLCC and OPL-3014 3mm through-hole lamp tables above, every color is rated at 20mA. Our advice: before comparing luminous intensity or voltage across parts, confirm the forward current is the same, or the numbers cannot be compared directly.
There are exceptions. Very small RGB parts such as the 0202 RGB common-cathode SMD LED specify red at 10mA and green and blue at 2mA. The three colors inside the same part have different current conditions, so each has to be calculated separately when you design the drive circuit.
Note that the forward current in the specification table is not the maximum current the LED can carry. The upper limit is the absolute maximum rating in the datasheet, and a real design usually keeps some margin below it.
Forward Voltage: Sets the Supply Voltage and the Current-Limiting Resistor
Forward voltage (VF) is the voltage across the LED at the forward current above. It depends heavily on the color. In the OPL-3014 3mm through-hole lamp, red, orange-red, amber, yellow and yellow-green are 2.0V or 2.2V, while blue, green and white are 3.2V. The 0202 RGB follows the same pattern: red is 2.1V, and green and blue are 2.8V.
Some product pages give a single value; others give a range. The OPS-L0828 side-view PLCC, for example, lists white at 3.2-3.5V, red at 2.0-2.6V, blue at 3.1-3.9V and green at 3.1-3.7V. When a range is given, size the power supply using the upper limit of the range so that no LED fails to light.
Once you know the forward voltage, you can calculate the current-limiting resistor: resistance = (supply voltage – forward voltage) / forward current. When several LEDs are connected in series, add their forward voltages together. For the full calculation and a 7-segment display example, see how to design the series resistor for a 7-segment display.
A worked example with our OPL-3014 (for illustration): with a 5V supply at 20mA, the red LRC30 has a forward voltage of 2.2V, so resistance = (5 – 2.2) / 0.02 = 140Ω; the white WC30 is 3.2V, so resistance = (5 – 3.2) / 0.02 = 90Ω. If one board mixes colors, calculate each resistor separately.
Luminous Intensity (mcd): Read It Together with Viewing Angle and Lens
The mcd (millicandela) unit in the table is the luminous intensity measured directly in front of the LED. For the same amount of light, the narrower the angle it is concentrated into, the higher the mcd reading on axis. So before comparing luminous intensity, check whether the viewing angle and lens are the same.
The white versions of the OPL-3014 3mm through-hole lamp are a good example:
| Part number | Lens | Viewing angle | Forward current | Forward voltage | Luminous intensity |
|---|---|---|---|---|---|
| OPL-3014WC30 | Water Clear | 30° | 20mA | 3.2V | 2800mcd |
| OPL-3014WD-60 | White Diffused | 60° | 20mA | 3.2V | 1600mcd |
Both are white, with the same current and voltage, and the 30° water clear lens shows a much higher mcd than the 60° diffused lens. That does not mean it is more efficient or “brighter”; the light is simply concentrated toward the front. For an indicator that must be visible from the side, the wider angle is actually the better choice.
Different colors within the same series also differ a lot in mcd. For example, the OPL-3014YGC30 is 900mcd while the OPL-3014PGC30 is 3000mcd. Order matters: decide the color from what your product needs first, then compare mcd within that color, not the other way round.
Dominant Wavelength and Chromaticity Coordinates: Define the LED Color
Single-color LEDs express their color as a dominant wavelength (nm). Shorter wavelengths are bluer; longer wavelengths are redder. On the OPS-L0828 side-view PLCC, blue is 470nm, green 525nm and red 624nm. Two parts can both be called “red” and still have different wavelengths: on the OPL-3014, the LEC30 is orange-red at 632nm and the LRC30 is red at 645nm. Placed side by side, the two colors look different. To see which colors cost less, read How to Choose the Lowest-Cost LED Color for Your Product.
White light has no single wavelength, so it is expressed as chromaticity coordinates or a color temperature. For example, the OPL-3014 white is specified at chromaticity coordinates X0.28 Y0.29, while the OPS-L0828 white is specified at a color temperature of 5250K.
The table below lists some of the OPL-3014 3mm through-hole lamp part numbers so you can see how forward voltage, luminous intensity and dominant wavelength change from part to part:
| Part number | Color | Forward voltage | Luminous intensity | Dominant wavelength / chromaticity coordinates |
|---|---|---|---|---|
| OPL-3014WC30 | White | 3.2V | 2800mcd | X0.28 Y0.29 |
| OPL-3014LBC30 | Blue | 3.2V | 2800mcd | 470nm |
| OPL-3014PGC30 | Green | 3.2V | 3000mcd | 525nm |
| OPL-3014YGC30 | Yellow-green | 2.0V | 900mcd | 572nm |
| OPL-3014LYC30 | Yellow | 2.2V | 1800mcd | 590nm |
| OPL-3014LAC30 | Amber | 2.0V | 1800mcd | 610nm |
| OPL-3014LEC30 | Orange-red | 2.0V | 1800mcd | 632nm |
| OPL-3014LRC30 | Red | 2.2V | 900mcd | 645nm |
An RGB LED has a separate dominant wavelength for each of its three colors. The 0202 RGB common-cathode, for example, is red 621nm, green 530nm and blue 469nm. For RGB packages and drive methods, see what is an RGB SMD LED.
LED Lens: Water Clear, Diffused and Colored Transparent
The lens column of a through-hole lamp usually shows one of three types:
- Water Clear: looks colorless and transparent when off. The light is more concentrated, so the on-axis mcd is higher.
- Diffused: for example White Diffused. The light is scattered, so it looks more even from the side, and the mcd figure is lower than the water clear version.
- Transparent (colored transparent): for example Blue Transparent. The lens itself is tinted, so you can tell the color even when the LED is off.
Take the blue versions of the OPL-3014: the LBC30 is 2800mcd, the LBT30 (Blue Transparent) is 2200mcd and the LBD-60 is 1600mcd. For green, the PGC30, PGT30 and PGD-60 are 3000, 2400 and 1600mcd respectively. Lenses follow the same logic: decide on the product appearance and viewing angle first, then check whether the luminous intensity is sufficient.
Package: Decide Between SMD and Through-Hole First
Beyond the specification table, the package determines how the LED is mounted on the board and which direction the light goes:
- SMD LED: surface-mounted, suited to automated assembly and thin products. Top-view types emit upward; side-view types emit sideways and are commonly used for light-guide backlighting. For package differences, see what is a PLCC LED; for products, see SMD LEDs and RGB SMD LEDs.
- Through-hole LED lamp (THT): the leads pass through the PCB and are soldered. It offers many lens and viewing angle options and is commonly used as a panel indicator. For an explanation, see what is THT / DIP; for products, see through-hole LED lamps.
Part Selection Checklist
| What you need to confirm | Which column to check | Watch out for |
|---|---|---|
| Which color | Dominant wavelength / chromaticity coordinates | Parts both called “red” can have different wavelengths; for white, check chromaticity coordinates or color temperature |
| Bright enough | Luminous intensity (mcd) + viewing angle + lens | mcd cannot be compared directly when the angle or lens differs |
| Supply voltage sufficient | Forward voltage | Use the upper limit when a range is given; add voltages together in series |
| Resistor and driver design | Forward current | RGB colors may have different currents; the upper limit is the absolute maximum rating in the datasheet |
| Mounting and light direction | Package, lens | SMD or through-hole; top-view or side-view |
Next Step: Find a Part Number and Request a Quote
Once you have settled on color, luminous intensity, voltage and package, go to standard LED products and filter by your requirements. Every product page includes a specification table and datasheet. After selecting, add the part numbers to the quote cart and submit them in one go. If what you need is a numeric or alphanumeric LED display and no standard part fits your size or font, see our custom LED display service.
FAQ
Not necessarily. mcd is the luminous intensity directly in front of the LED, and the narrower the angle, the higher the number. For an indicator that must be clearly visible from the side, a part with a wider angle and lower mcd is often the better fit. When comparing luminous intensity, first confirm that the viewing angle and lens are the same.
Forward voltage depends on the emitted color. Taking OPTO PLUS products as an example, red, yellow and orange types are a little over 2V, while blue, green and white are a little over 3V. When mixing colors on the same board, calculate the current-limiting resistor for each color separately.
No. The forward current on the product page is the test condition for the luminous intensity and forward voltage, not the absolute maximum rating. For the maximum current the LED can handle, refer to the datasheet in the “documents” column of the product page. If you have special current or luminous intensity requirements, add the part number to the quote cart and confirm with us.