Introduction

LED lighting is fast replacing traditional incandescent and fluorescent lighting due to benefits like high energy efficiency, long life and design flexibility. At the heart of an LED lighting product are the LED chips which provide the illumination. Choosing the right LED chips is crucial for achieving the target light output, efficiency, color characteristics and reliability.

This article discusses how to select appropriate LED chips for lighting design including parameters like power, luminous efficacy, color temperature, CRI index and thermal management. Read on for practical guidance to pick optimal LEDs for your lighting application.

Key LED Chip Specifications

The main parameters that characterize an LED chip are:

Power Rating

• Measured in Watts
• Determines light output
• Options range from 0.2W to over 10W

Forward Voltage

• Typical values between 2V to 4V
• Impacts the driver design

Luminous Efficacy

• Measure of light output vs input power
• Given in lumens/Watt (lm/W)
• Higher is more energy efficient

Peak Wavelength

• Determines color – 620-630nm is red, 520-535nm is green etc.
• For white LEDs, blue chip + yellow phosphor is common

Color Temperature

• Warm white, neutral or cool white
• Measured in Kelvin (K)
• 2700-3000K is warm white, 5000-6000K is cool white

CRI Index

• Color Rendering Index
• Rating of color quality – maximum of 100
• Higher CRI gives better light quality

Viewing Angle

• Beam width at 50% intensity points
• Narrow (15°), medium (25-50°) or wide (120°+) available

Lifetime

• Hours of operation before light output declines by 30%
• 30,000 to 100,000 hour lifetimes are common

Package Type

• Surface mount or through-hole LEDs
• Defines how it’s soldered to PCBs

Key Considerations for LED Chip Selection

Primary aspects to consider when choosing LED chips for lighting include:

Target Luminosity

• How much visible light is needed for the application?
• Select chips with lumen output in required range

Efficiency

• Higher lumens/watt improves energy efficiency
• Balances luminosity vs power consumption

Color Temperature

• Depends on lighting ambiance needed
• Warm, neutral or cool white?

Color Quality

• Higher CRI gives better light quality
• CRI 80+ is desirable for most lighting

Operating Life

• Lifetime of LED chips should match product life
• Select chips with 50,000 hours or greater lifetime

Thermal Management

• LEDs produce heat which impacts performance
• Ensure ambient temperatures are within chip rating

Driver Interface

• Forward voltage and constant current needs
• Match to chosen LED driver design

Physical Size

• Overall dimensions and pad spacing
• Ensure PCB layout accommodates chip package

Budget

• Balance performance vs unit cost of LED chips

Let’s look at some of these aspects in more detail.

LED Chip Power Ratings

Available LED chip power ratings include:

• Low power: 0.2W to 0.5W
• Medium power: 1W to 3W
• High power: 5W to 10W

Higher power LEDs produce greater luminous output. But the increased heat needs thermal management.

For most general lighting like bulbs, downlights and strips, mid-power 1W to 3W LED chips offer a good compromise between light output and easier thermal control vs high power chips.

But specialty lighting like high bay lighting may use higher 5W-10W LEDs. While battery powered flashlights can use tiny 0.2W-0.5W chips.

Lumen Output

The lumen rating of LED chips depends on the power and efficacy. Various luminosity bins are available for each LED chip ranging from low to high lumens.

Typical lumen output for various power LEDs:

• 1W LED chip – 100 to 130 lumens
• 3W LED chip – 250 to 300 lumens
• 5W LED chip – 400 to 500 lumens
• 10W LED chip – 900 to 1000 lumens

Select chips with lumen output that meet the application’s illumination needs. Combine multiple lower lumen LEDs for higher brightness.

LED Chip Efficacy

Higher efficacy or lumens/watt improves lighting energy efficiency. LED chip efficacy has increased enormously over the years due to technology improvements.

• Older LED chips had efficacy of 30-60 lm/W
• Mid-power modern LEDs now achieve up to 90-120 lm/W
• High power LEDs range from 100-150 lm/W

For a given power rating, choose LED chips with the highest efficacy within budget. This maximizes light output vs power consumption.

Color Temperature

Color temperature determines the visual color tone of white light – from warm white to cool white.

Common white LED color temperatures:

• Warm white: 2700K to 3000K
• Neutral white: 3500K to 4100K
• Cool white: 5000K to 6500K

Warm white is commonly used in homes for cozy lighting. Cool white is preferred where brighter illumination is needed. Select color temperature depending on lighting ambiance needed.

CRI Index

The Color Rendering Index (CRI) indicates how accurately colors are displayed in the light.

• Low CRI like 70-75 gives poor color
• Medium CRI of 80-90 is generally acceptable
• High CRI > 90 approximates natural light

Aim for LED chips delivering 80+ CRI for quality lighting applications. chips with CRI 90+ can provide near natural color rendition.

LED Chip Lifetime

LED chips last much longer than traditional light sources. But over time, light output gradually declines due to phosphor degradation.

• 30,000 hours is minimum lifetime needed
• 50,000 hours is typical for quality mid-power LED chips
• 100,000 hours lifetime LEDs are used for extra reliability

Match the LED chip operating life to the target product lifespan. Also factor in ambient temperature which affects LED lifetime.

Thermal Management

LED chips generate significant heat. Operating at high temperatures lowers light output and shortens lifetime. Effective thermal management is vital.

• Use quality aluminum PCBs or ceramic substrates to conduct heat away from the LED chips.
• Thermal interface materials like epoxy or grease improve heat transfer to the board.
• Ensure ambient air temperature around LEDs stays within recommended range.
• Allow spacing between LEDs for airflow to limit temperature rise.

Proper thermal design greatly improves LED chip performance and longevity.

LED Chip Packages

Common LED chip package types include:

• SMD – Low profile surface mount devices, easy to solder
• COB – Chip on board arrays, combine multiple LEDs
• Through-hole – Used for screw based bulbs
• Ceramic substrates – Provide electrical isolation

SMD packages allow easier PCB assembly while COB arrays simplify optics design. Consider package height restrictions and soldering processes when selecting.

Conclusion

Choosing optimal LED chips by carefully evaluating key parameters like power rating, luminosity, efficiency, color characteristics, lifetime and thermal management enables creating energy-efficient, long lasting and good quality lighting products. Leverage the latest mid-power and high-power LED chips to realize substantial energy savings and simplified lighting design. With technology advancements delivering ever more performant LED chips, lighting product developers can take advantage by selecting the most appropriate chips to meet their precise application needs.

FAQs

What are the main differences between mid-power and high-power LED chips?

Mid-power LEDs (1-3W) strike a balance between light output and easier thermal management. High-power LEDs (5-10W) produce higher brightness but require substantial heat sinking.

How important is the PCB design for an LED lighting product?

Proper PCB thermal management through large copper planes, thermal vias, airflow and heat sinks is crucial to ensure LED chips operate at optimal temperature for maximum light output and reliability.

What causes LED chips to degrade over their lifetime?

Operating LED chips at high junction temperatures accelerates luminous decay, color shift and failures over time. Quality encapsulation also protects against moisture ingress and corrosion.

Can the color temperature of white LEDs shift over their lifetime?

Yes, white LEDs can gradually shift to a bluer tone over tens of thousands of hours of use. Higher quality LED chips exhibit better color consistency throughout their lifetime.

How does photon efficiency relate to LED efficacy?

Photon or wall-plug efficiency defines the LED chip’s inherent ability to convert electrons to photons. Maximizing this improves luminous efficacy (lumens per watt). Chip design, materials and packaging maximize photon efficiency.