In short
- Start from the viewer. Viewing angle, color and brightness decide whether the LED does its job for the person looking at it.
- Respect the ratings. Drive the LED at its rated current with a matched driver or resistor. Overdriving shortens its life.
- Count the power. Efficiency (light per watt) and total power add up over the product’s life.
- Use the package. Arrays, 7-segment displays and LEDs with built-in resistors or blinkers save board space and design time. And sometimes a laser is the better source.
Light-emitting diodes (LEDs) have been around since the 1960s and are used in a huge range of applications. They offer advantages that other light sources cannot match. Common uses include monitors and displays, consumer and advertising lighting, laboratories and industry.
Because the choice is so broad, here are ten tips for choosing the right LED and the right configuration. For the physics behind them, see understanding LEDs: from basics to applications.
1. Viewing angle
LEDs are bright, but what matters to the end user is the angle they see it from. Reflective surfaces inside an LED package can concentrate the light into a narrow cone, so the LED looks dim from the side. A wider viewing angle widens the range of angles from which a display or indicator is easy to read.
2. Power consumption
Consider how much power is available and how much the LED may use. Managing consumption saves battery or mains power, and money for the end user. Stay within the manufacturer’s specified parameters: driving the LED above its recommended power is possible, but it shortens the diode’s operating life.
3. Efficiency
The brightness of a visible LED is specified as luminous intensity, in candela (cd), or millicandela (mcd) for small indicators. Luminous intensity is the power emitted in a given direction, weighted by the sensitivity of the human eye. Efficiency, or luminous efficacy, is how much light the LED produces per watt of electrical power: the higher it is, the more light for the same power. Options range from standard LEDs to super-bright and ultra-bright LEDs for specialized uses. For the units in detail, read the basics of light measurement: radiometry and photometry.
4. Total power
Power matters both ways: too much damages the LED, too little may not meet its purpose. A high-power LED may draw 1 W, while a low-power indicator draws around 100 mW. Over the life of a product, and over many units, the difference adds up significantly.
5. Color options
LEDs come in many colors. Amber, green and red are the traditional ones; blue, violet and white are now common too.
Most “white” LEDs combine a blue or near-UV (NUV) diode with phosphors. A common design uses a blue pump diode at 460–470 nm with a phosphor whose broad emission is centered near 540–550 nm. Together they look white, but the spectrum lacks cyan and red, so skin tones, artwork, flowers and fabrics can look unnatural. Many makers add auxiliary red LEDs to compensate.
NUV-pumped white LEDs usually use three phosphors (red, green and blue) as the main light source, with little contribution from the pump itself. The result is a more balanced spectrum and a higher color rendering index (CRI).
White light from separate RGB LEDs is possible but uncommon, because matching the color of three LEDs is difficult. Current, temperature and aging all shift each LED’s output, so consistent color often needs closed-loop feedback. RGB LEDs are mainly used where the color must be chosen freely and continuously. Their drawback: intermediate colors fall between the narrow bands of the three LEDs, which can cause metamerism (also seen with phosphor white LEDs). Some designers prefer RGB for its high saturation.
The semiconductor material sets the color: GaN for blue, GaAsP or InGaAlP for red, and GaP for green.
6. LED drivers
For consistent light output and a long life, an LED needs the current specified in its datasheet. An LED driver provides it, usually as a constant-current supply matched to the specific LED. For simple indicators, a series resistor sets the current from a fixed supply; the tool below sizes it.
Dimming is done with pulse-width modulation (PWM): the LED is switched on and off faster than the eye can see, and shortening the duty cycle lowers the perceived brightness.
LED series resistor and PWM calculator
Enter the supply voltage, the LED forward voltage and current from the datasheet, how many LEDs are in series, and the PWM duty cycle. The tool sizes the resistor, picks the nearest standard (E24) value and shows the power in the resistor and the LEDs.
Model: R = (Vsupply − n × Vf) ÷ I; the E24 value is the next standard value at or above R, so the current stays at or below the target; actual I = (Vsupply − n × Vf) ÷ R(E24). Power while on: resistor I² × R, LEDs n × Vf × I; average power and current = value while on × duty cycle. Drive efficiency = n × Vf ÷ Vsupply. Suggested resistor rating is at least twice its average power. Vf changes with current and temperature, so check the current on the real circuit; for power LEDs prefer a constant-current driver.
7. Packaging
LEDs come in many physical packages. The common round, cylindrical-top versions are 3 mm, 5 mm and 8 mm. A 7-segment package suits numeric displays, especially clocks and timers; a 7-segment decoder IC turns the digital signal it receives into the correct digit.
8. Multiple LEDs in one package
Several LEDs can be bought in a single package: strips, rows, strings or multi-digit displays. This reduces circuit complexity and engineering time, and one power source or control IC can often drive the whole group. Note that the current and power requirements of multi-LED devices differ from those of single LEDs.
9. Built-in controls
Some LED packages include control circuitry, such as an astable multivibrator that blinks the LED or creates other timing patterns. An LED can also come with a built-in current-limiting resistor. It works within a specified voltage range, saves board space and suits compact designs.
10. LEDs are not always the best option
LEDs suit a great many applications, but when you need coherent light, a narrow beam or high brightness at a distance, a laser may be the better source. If you go that way, a laser beam profiler verifies the beam you get.
Did we miss a useful tip? Tell us, and we will add it.
Verify the LEDs you chose
Once the LED is chosen, check that every unit meets its specification: color and intensity in the lab with an integrating sphere and a multi-channel spectro-radiometer, and function, color and position on every assembled board with the IZAK LED tester.
Frequently asked questions
QWhat should I look at first when choosing an LED?
QHow do I calculate the resistor for an LED?
QWhy do white LEDs render colors poorly?
Tzachi Sabati
CEO, IZAK Scientific
Physicist specializing in photonics and quantum technologies, with deep expertise in quantum sensors and advanced optical systems. Leads the Advanced Quantum Lab course at the Technion, bridging academic excellence with industry innovation. At IZAK Scientific, provides cutting-edge photonics-based solutions, developing customized inspection and sensing systems for R&D and production. Passionate about advancing quantum sensing applications and integrating novel technologies to meet industry needs.
