Understanding Color Temperature




What is color temperature? What is CRI? In this blog post we try to explain what it is and why it is important.

Lamps are often rated by:

  • Power consumption and light output – in Watts (Unit of electricity consumption), Lumens, Lux or Candela (Units of light output), Lumens per Watt (A derived unit that indicates the luminous efficiency of the lamp).
  • Color Rendering Index – A measure of how efficient is a lamp at reproducing colors.
  • Color Temperature – an indicator of visual light color


Of late, a new parameter called ‘Pupil Lumens’ has entered the picture. The light output of a lamp is expressed in photopic lumens. Pupil lumens on the other hand measure the impact of different wavelengths of the eye on vision under Mesopic light conditions.

You can refer to other resources on this site to know more about power consumption, light output, Color Rendering Index and Pupil Lumens.  Below is a discussion of Color Temperature meant to help you choose the right LED technology product.


Color Temperature

Color temperature of a light source is “the temperature of a black body radiator in Kelvin (K) that radiates light of a hue that is similar to that produced by the light source.” This definition may be a bit confusing for people not familiar with the physics behind light. A simpler explanation of color temperature would therefore be more appropriate.

When the first developments in lighting technology occurred, the only way to produce light was to heat an object. When an object was heated – either by passing a current through an electric wire or by other means – it first became ‘red hot’ and then went on to become ‘white hot’ as the heating continued. 

A ‘red hot’ object has a temperature close to 600 degrees centigrade. By comparison, a ‘white hot’ object may have a temperature of 7000 degrees or more. If you have seen a glowing ember (600 centigrade temperature, with very little light output), it is easy to understand that at lower temperatures almost all the energy is converted to heat. At higher object temperature, the production of light improves. Thus, energy from the sun consists of 40% light and 60 % heat while a light bulb emits 10% or less energy as light and 90% as heat.

Here are the temperatures of a few light sources

 Light Source
Temperature
 Glowing ember  900K
 Match flame 1700K
 Incandescent Bulb 2700-3300K
Sun at sun rise or sun set  3000K
Sun at noon  6500K

 

The incandescent bulb is very close to the ideal black body radiator. Other sources of light including metal halide, fluorescent and LED lights produce lights by processes other than heating. Instead of color temperature, the term Correlated Color Temperature (CCT) is at times applied to these light sources and is a good yardstick for comparing different sources of light.

Lights of 3 different Color Temperatures. Note that the light from 6000K lamp is bluish in color.


Importance of Color Temperature

Color temperature is particularly important in photography and desktop publishing. Differences in color temperature can result in variations in color rendering.

In homes and offices, color temperature of lights is important as different colors of light have different psychological impacts and are designated as ‘warm’ or ‘cool’. Ironically, the so-called ‘warm lights’ have a lower ‘Color Temperature’ while the ‘cool lights’ have a higher ‘Color Temperature’. Warm and cool thus refers not to the color temperature but to psychological attributes of lighting. The light from wood burning fires and incandescent bulbs is yellowish in color.

The human mind, conditioned by thousands of years of social evolution, accepts yellow-ish light as warm and inviting. On the other hand, day white light is associated with cleanliness and efficiency - as in hospitals. IT is also depending on cultural and regional backgrounds as people form countries nearer to the equator prefer cold white light sources than warm white lights.

The choice of light color temperature is governed by the look you wish to create in an area. Lights of different color temperature are described by their similarity to known sources or with typical adjectives. The table below can help you choose the right lamp for your needs
 

Lamp Color Name Apparent Color Temperature (Kelvin) Characteristics and Examples Common Adjectives Used to Describe the Light Best Location
Warm White  2700-3200K Similar to incandescent bulb, yellowish light best  for accentuating skin tones and color of wooden objects Friendly, warm, inviting, intimate, relaxing Best for areas that need low light intensity like Bedrooms, lounges, restaurants, office lobbies, boutiques, reception area etc.
Natural White  4000-4500K Similar to early morning sunlight, Xenon lamp for automotive use Neat and clean, Natural tone Best choice for high light intensity applications like  Surgical lights, indoor photography, Laundry, Office etc.
 Day White  5500-6000K Typical day light, Flash light. Crisp light, efficient, brightly lit, natural outdoor Retail stores, Factories, Printing, artist studio, Schools, Offices, indoor grow lights, photography
 Cool White  7000-7500K Best contrast but least flattering to the skin, may need mixing with light from a warm white lamp. Bright light, bluish light Special applications needing high light intensity and good color rendition like art Galleries, museums, showcases for precious stones and jewelry

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