LED Kelvin - Learning Objectives

1. What does Kelvin Temperature mean?
2. What is warm and cool light?
3. Is Color Temperature on Lighting Facts packaging?

What is Kelvin Temperature?

Since LED light sources do not mimic daylight, there is a need to have some metrics for comparison to familiar light sources of daylight, incandescent and halogen.

Warm or cool temperature?

Kelvin temperature is a number that indicates a point on the Warm - Cool Scale and connects the color temperature of a light source to a known value. The lower the number the warmer the light - up to 3000K is considered warm and seems yellowish or reddish.
5000K is considered cool indicating more bluish light. You would expect that the 4000 range to be in the middle, it will appear warm or cool depending on what is being illuminated, the surrounding wall color, and the amount of bias of the light source.

What color is sunlight?

Natural daylight ranges from 4000K to 27,000K. Daylight contains all colors, so we can see all colors, if the color is not in the light source, then it cannot reflect the color back to your eye or camera. See more about color wavelengths on our Color page.

Natural & Artificial Light measured in Kelvin

Light Source	Kelvin
Candle	1700K - 2000K
Turtle Friendly	570nm or 1700K [1] [2]
Low Pressure Sodium	589nm 1740K
High Pressure Sodium White Son	2700K
HID	3000K - 20000K
Incandescent	2500K
Halogen	3190K - 3500K
Noon Sunlight	4000K - 6500K
Overcast Sky	6500K - 7500K
Northern Sky	8000K
Blue Sky	15000K - 27000K
Moonlight	4100K

 LED = Light Emitting Diodes - now the standard for new construction in the state of California, mandated by Title 24 energy code power limits, the most restrictive power allowances in the world, preceding adoption of similar codes worldwide. LED bulbs (or lamps as the lighting industry calls them, or Light Engines as the lighting designers call them) are inherently color biased. Since the Blue White chip was developed for the commercial market, manufactures have been struggling with achieving balanced white light.  A combination of coatings, voltage, age, and manufacturing processes all affect an LED's spectral and lumen output, industry terms for color and brightness.
Good lighting design should always include analysis of color rendering, light intensity, beam spread, flicker, and glare.

Retail packaging Lighting Facts includes CCT - Correlated Color Temperature a bar graph from warm to cool showing  - Light Appearance in Kelvin

• CCT - Correlated Color Temperature -K = Degrees Kelvin, or color temperature of the light

DOE - Department of Energy
Lighting Facts

 Standard Label with Optional Metrics Anatomy of the LED Lighting Facts®  Correlated Color Temperature (CCT)

• Measures light color.
• “Cool” colors have higher Kelvin temperatures (3600–5500 K).
•  “Warm” colors have lower color temperatures (2700–3500 K).
• 2200K is considered candlelight, 10000K is considered daylight at high-noon.

Other color rendering indicators include CRI, R9, TM-30
Consult individual LED manufacturer for published test results.

Related Topics

Manufacturer's Educational Links, LED for your B&B, Color in Paint - Why they Fade

Footnotes

1. How are hatchling sea turtles able, and unable, to locate the sea?  page 127  http://www.nmfs.noaa.gov/pr/pdfs/species/turtlesymposium1991.pdf
2. https://conserveturtles.org/project-overview-stc-beachfront-lighting-program/
   
3. www.lightingfacts.com​

Photo Credits

• Lighting Facts Card - DOE - Department of Energy
• Test Colors for CRI & Light Source Color Rendering Chart - EYE Lighting
  
• TM-30 Test Colors - IES TM-30-15 Errata