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.
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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.
The main parameters that characterize an LED chip are:
Measured in Watts
Determines light output
Options range from 0.2W to over 10W
Typical values between 2V to 4V
Impacts the driver design
Measure of light output vs input power
Given in lumens/Watt (lm/W)
Higher is more energy efficient
Determines color – 620-630nm is red, 520-535nm is green etc.
For white LEDs, blue chip + yellow phosphor is common
Warm white, neutral or cool white
Measured in Kelvin (K)
-K is warm white, -K is cool white
Color Rendering Index
Rating of color quality – maximum of 100
Higher CRI gives better light quality
Beam width at 50% intensity points
Narrow (15°), medium (25-50°) or wide (120°+) available
Hours of operation before light output declines by 30%
30,000 to 100,000 hour lifetimes are common
Surface mount or through-hole LEDs
Defines how it’s soldered to PCBs
Primary aspects to consider when choosing LED chips for lighting include:
How much visible light is needed for the application?
Select chips with lumen output in required range
Higher lumens/watt improves energy efficiency
Balances luminosity vs power consumption
Depends on lighting ambiance needed
Warm, neutral or cool white?
Higher CRI gives better light quality
CRI 80+ is desirable for most lighting
Lifetime of LED chips should match product life
Select chips with 50,000 hours or greater lifetime
LEDs produce heat which impacts performance
Ensure ambient temperatures are within chip rating
Forward voltage and constant current needs
Match to chosen LED driver design
Overall dimensions and pad spacing
Ensure PCB layout accommodates chip package
Balance performance vs unit cost of LED chips
Let’s look at some of these aspects in more detail.
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.
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
Contact us to discuss your requirements of LED Encapsulation Materials for General Lighting. Our experienced sales team can help you identify the options that best suit your needs.
5W LED chip – 400 to 500 lumens
10W LED chip – 900 to lumens
Select chips with lumen output that meet the application’s illumination needs. Combine multiple lower lumen LEDs for higher brightness.
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.
LED Aluminum Substrate
Color temperature determines the visual color tone of white light – from warm white to cool white.
Common white LED color temperatures:
Warm white: K to K
Neutral white: K to K
Cool white: K to K
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
LEDs come in a huge variety of styles. We'll take a look at the most common features:
Mounting Types
There are three common way in which LEDs can be mounted:
Through Hole (THT)
Surface Mounted (SMD)
Screw mounted or thermal adhesive
THT components might be what you are most familiar with: Their pins go through holes in a PCB and are soldered on the other side.
SMD parts are soldered directly to the surface of a PCB. With this method they can be made much smaller than THT parts and are perfect for tiny projects, such as wearables. On the flipside they are more difficult to solder.
Some LEDs, especially power LEDs are mounted on an aluminum or ceramic substrate to improve the cooling. They are meant to be mounted with either screws or a thermal adhesive.
Optics
The LED chip itself produces a wide beam of light (about 120°). To make it suitable for spotlights a clear dome is placed right above the chip to act as a lens. Some LEDs, so called diffused LEDs, don't have any beam at all, they evenly scatter the light in all directions. This is very useful for indication LEDs as the light is visible from any direction.
Multi-Color/ RGB LEDs
You may have seen LEDs with multiple chips for different colors into one case. With such LEDs you can not only select the color you want, but also mix the light to get any color in between! We'll come back to this in "Chapter 3: Switching & Dimming".
Often it is not possible to have two dedicated pins for each LED chip, in such case either the anodes or cathodes are connected internally to only one common pin.
LED Matrix
Similar to Multi-Color LEDs these contain multiple LEDs in one package, but usually all the same color. They are also available as both, common anode and common cathode configurations. They can be used to display text or numbers and are readable from quite afar. However the high LED count usually requires a micro-controller and multiplexing. In "Chapter 4: Matrix & Multiplexing" we'll dig deeper into this.
7 Segment Display
While numbers can be displayed with a simple LED matrix, a seven segment display provides a much more elegant solution with way less LEDs you need to control. Alphanumeric displays are based on the same idea, but with a total of 14 or 16 segments they can show in addition all uppercase English letters. Electrically this kind of display is identical to the common LED matrix.
Integrated circuit
No matter the light effect you want, with some effort everything is possible. For the most common effects, such as blinking or color cycling, you don't even need to invest that much time. Some LEDs come equipped with a tiny circuit to do just that.
A very special LED is the WS/ WSB, sold as "Neopixel" by Adafruit. The chip inside takes serial data from a micro-controller (such as an arduino) and controls the RGB LED to match that!
No matter which LED you decide to get, check the datasheet briefly, so you don't miss anything important.
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