LED Lighting Half-Baked or Ready for Prime Time?

Presented By: Michael Stiller, LEED AP, IESNA Principal Designer, Michael Stiller Design

Section 1: LED Sources

Program Information

•  A handout of this presentation is available for download on the IES Education website.

•  This program qualifies for (0.5) IES CEUs. A certificate of attendance will be available for viewing this presentation

•  Please download the IES Form 2 Survey and return it via electronic email to: pmcgillicuddy@ies.org

Learning Objectives

This seminar (sections 1 & 2) will enable participants to:

• Compare LED lighting sources with regard to color consistency and efficacy.

• Specify LED lighting fixtures that are manufactured to the relevant standards as defined by the IES and incorporate sources that are manufactured to the relevant standards by ANSI.

• Analyze the suitability and economic feasibility of specific LED lighting fixtures and lamp retrofits as replacements for existing conventional lighting.

• Identify existing environmental conditions with an eye towards determining how they will affect the performance of LED lighting.

LED (SSL) Basics SSL = Solid State Lighting LED = Light Emitting Diodes

Typical 5MM LED Indicator Lights, Traffic Signals

Line of Sight Applications

Typical High Flux LED Lighting Fixtures & other

High Brightness Applications

LED Basics (Light Emitting Diodes)

Electroluminescent Diode From Semiconductors: Chemical Elements or Compounds

LED’s are made from various inorganic semi-conductor materials, each producing a different color of light.

LED’s are made from various inorganic semi-conductor materials, each producing a different color of light.

There’s No Such Thing As A White LED!

How To Make White Light Then?

RGB (Red Green Blue) = Additive Color Mixing System

Additive Color Mixing

RGB(A) & Other Color Mixing LED Fixtures Can Mix to “White”

Issues: •  Multi-Colored Shadowing/Fringing & Mixing Artifacts

(solved by tri-node LED’s) •  LED’s Not True Primary Colors (Mixed White’s Not Pure)

Theatrical Lighting: An Early Venue For LED’s

Great Light Losses (inefficiency) When Using Colored Filters With Conventional Lighting

The Most Common way To Make White Light For Architectural Applications Is By Using a Blue Diode With A Yellow Phosphor

High Flux, White LED

Components: Die, Reflector, Lens (optics), PC Board (substrate), Thermal Slug

Remote Phosphor

• Recovers & Redirects Scattered Light More Efficiently • Enables the use of one phosphor coating for an LED array • Avoids Variables Associated With Applying Phosphor Directly To The Diode/Helps Maintain Color Consistency

Color Consistency: How Do We Get There?

Chromaticity Chart Showing Planckian Locus: “White Light”

ANSI Standard

ANSI Standard Specification for LED Chromaticity (Correlates to DOE CFL Specification) Categories Are Defined by Target Color Temperatures Within an Acceptable Range

Diode Binning

Different LED Manufacturers Define Their Bins Differently

Diode Binning

Different LED Manufacturers Define Their Bins Differently

Bins Are Getting Tighter…

Compared to the ANSI 7 Step McAdams Elllipse/CFL Standard

…And Tighter…

Compared to the ANSI 7 Step McAdams Elllipse/CFL Standard

Some Other Causes of Color Variations in LED Lighting Systems

Optics • Color shift in lens materials and/or coatings

• Electronics • Drive current accuracy and consistency • Color sensor and/or temperature sensor accuracy

LED array • Selection of available bins • Temperature variation over board

LED Node • Variation in phosphor concentration/layer thickness • Binning versus use temperature

• Environmental • Temperature changes (heat buildup)

Color Consistency/Uniformity

Why Do We Care?

CRI (Color Rendering Index): A Useful Metric?

• Color Rendering Index = the measurement of a light sources ability to accurately render a sampling of different colors, as represented by a scale from 1-100.

• Developed in the mid 20th century in response to the advent of fluorescent and HID sources.

• High Color Rendering fluorescent lamps are characterized by a CRI of 85 or greater.

• CRI is a controversial metric today, especially among the LED lighting community.

• The NIST is developing a new Color Quality Scale.

• Use this metric as a guide, but seeing is believing!

Incandescent Daylight Fluorescent LED

Best Way To Judge Color Quality? Plug ‘em in and Turn ‘em on

This is White Light?

What The Manufacturers Say

Philips: Proper thermal design is imperative to keep the LED emitter package below its rated operating temperature.

Cree: The majority of LED failure mechanisms are temperature dependent. Elevated junction temperatures cause light output reduction and accelerated chip degradation.

Osram: In order to achieve reliability and optimal performance a proper thermal management design is absolutely necessary.

Nichia: For high power LED applications, the designer must consider how to manage heat, in order to enhance the performance of the LEDs. If heat management is not considered, the lifetime of the LED will be significantly decreased, or the LED will fail.

Thermal Management

Thermal Management

A Properly Designed Lighting Fixture Will Incorporate All These Elements In Some Form

Thermal Management

A p–n junction is formed by joining P-type and N-type semiconductors together in close contact. The term junction refers to the boundary where the two regions of the semiconductor meet.

Thermal Management

Heat Sinks Can Be Hidden From View Or Integrated Into A Fixture’s Exterior Casing. All LED Fixtures Should Feel Warm When Operated For More Than A Few Minutes!

Lifetime (Lumen Maintenance) LED’s don’t die, they just fade away.

• Useful LED life is defined as the period of time after which the lumen output of the LED source has depreciated to 70% (L70).

• Today’s well designed LED fixtures can be expected achieve a useful life of approximately 50,000 hours.

• In LED sources, factors that contribute to lumen depreciation include drive current and heat generated within the device. Some white-light LEDs may experience degradation of the phosphor coating . Some LEDs can also suffer from clouding of or impurities in the encapsulant used to cover LED chips.

• These conditions vary with the design of different fixtures, the drivers incorporated in each, the fixture’s thermal management, and their method of incorporation within the architecture.

Thank You!

The Illuminating Engineering Society of North America

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New York, NY 10005212-248-5000

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