Reliability & Standards for Color-Tunable Products

Jim GainesDOE R&D Workshop

Dallas/Fort Worth Jan 29-31, 2019

Basics of Color Tunability

Color-tunable light source reliability

Factors that affect color (temperature, time,…)

Interdependence of color and non-color parameters

Color reliability example: Philips Hue

Standards for Color-tunable products

Energy Star, Design Lights Consortium, IEC, IES

Thoughts for future standards

Outline

2

3

Basics: Location of primaries

Large color gamut

High sensitivity

Reduce color gamutLower sensitivity

Trade Off:

Color gamutvsColor consistency

4

Reliability

Three basic problems with LED light sources (tunable or not): Lumen depreciationColor shiftCatastrophic failures

All problems are still present for color-tunable systems, but with some extra concerns:

More components (multi-channel driver, multiple LED primaries, color mixing optics, sensors)

Lumen and color maintenance intertwine →More possibilities for color degradation

This talk focuses on the color maintenance issues.

5

Single primary: Lamp color change is determined by color change of only one primary.

Color change with > 1 primary is determined by: • color change of each primary, plus• relative intensity change of the primaries.

Causes of differential changes in intensity:• Temperature changes. If the red LED has a different temperature dependence

than the blue or green, the color will shift as the lamp temperature rises. • Lumen depreciation

For high color reliability, the control system must correct for these!

Example: Early candle lamps contained both white and red LEDs – for high CRI. No temperature feedforward. There were complaints about the pinkish color during warm up.

Color Control with Multiple Primaries

L Prize: Color Maintenance

6

31 LampsBest: ∆u’v’ = .001Average: ∆u’v’ = .002Worst: .005

https://www.energy.gov/sites/prod/files/2018/06/f52/LPrize_60W-LumenMaintTesting_2016.pdf

Performance of Color Tunable products is not constant

7

Flux

Efficacy

Color Rendering

Power (Factor)

…

3 Primaries – 1 surface for each parameter.Multiple surfaces if more than one parameter can be controlled simultaneously.

Performance of Color Tunable (Philips Hue) product

8

Color Control – Philips Hue

9

Thermal feedforward

At any set operating condition: Measure heat-sink temperatureCalculate shifts of each primary (R, G, B,…):

ColorFlux

Adjust driving of primaries to meet target operating condition

Thermal feedforward cannot compensate for (differential) flux depreciation over time. Two ways to address:

• Optical feedback • Gentle driving, to minimize depreciation over rated life

Reliability – Philips Hue

10

Reliability – Philips Hue

11

Approaches to Color Tunable Products in Standards/Specifications

12

Published: Energy StarDesignLights Consortium (white-tunable only)

In progress: IECIES

Energy Star

13

Test and evaluate at the most power-consuming white light setting. (One LM79 test)LM80’s for each primary.Report values at default setting.

• At any other setting of the lamp, energy is being saved. Efficacy, etc are irrelevant, from the point of view of energy savings.

• It is not possible to test every setting.

Simple, Straightforward

Regulators/specifiers don’t need to verify/control performance at every setting!• Keep test burden low• Avoid unintended consequences

DLC“White-Tunable products must meet the DLC Technical Requirements at all values of the color control signal for the General Application(s) and Primary Use(s) for which they are submitted, except for CCT. This includes minimum light output, efficacy, CRI, lumen maintenance, THD, Power Factor, and zonal distribution/spacing criteria requirements.”*

Recipe for infinite testing

Reduced somewhat, in testing requirements, to:

• Minimum CCT input control setting

• Maximum CCT input control setting

• One intermediate point

• Least efficacious

• If the above doesn’t include 1) min lumens, 2) min nominal CCT, 3) max nominal CCT, 4) min CRI, 5) highest power, 6) worst power quality, then test more at worst case for: Photometric distribution, lowest lumen output, min CCT, max CCT, min CRI, highest power, worst power quality (PF AND THDi)

14

*https://www.designlights.org/solid-state-lighting/qualification-requirements/product-eligibility/?scrollTo=color-tunable-products

Difficult specifications

15

Well-intentioned specifications can cause problems.

M: But highest light output is at a condition where CRI is undefined! Does my product fail, since I’m also supposed to meet the CRI spec?

M: But I can pick 10,000 settings that are at 50% of the maximum! Which do you want?

R: OK. Just use 3000K then!

M: But my 4-primary light source can change saturation. There are still 100 settings! Which do you want?

R: Just test them all!

*&%#! +?@$!

Conclusions

16

Color control at the level required for general lighting is possible.

It is complicated – you must take care of more details than for fixed white.

Some standards exist, and others are coming. Some are good. Some have problems.

Keep it simple in any regulations