Color Temperature and CRI of Energy Saver Lamps
by LJ Martin
People often complain that they do not like fluorescent energy saver lamps because of the color they produce. However, all energy savers are not equal. This guide will explain Color Temperature and Color Rendering Index (CRI), which will help you to choose which energy saver lamps to buy.
This is a measure of how warm or cool the light given off by a lamp appears, with warmer colors having a yellowish tinge and colder colors being tinged with blue. What confuses some people is that the warmer a color is, the colder its color temperature is. This is because something which is red hot is actually colder than something which is white hot (which makes sense when you think about it) but psychologically the bluish white object seems colder as we associate blue with cold.
Figure 1: Color Temperature
Color temperature is measured on the Kelvin (K) scale, which uses the same units as the Celsius or Centigrade scale, but starts at absolute zero (-273 degrees Celsius). A warm white lamp similar to an incandescent bulb has a color temperature of around 2700K, and gives off light with a yellowish quality, while 6000K represents a bluish white color as shown in Figure 1. This is called color temperature because theoretically if you were to heat something up to 2700K it would glow yellowish-white, and if you heated it to 6000K it would glow bluish-white (Though there is no material that you could actually heat up to 6000K without destroying it). This is how an incandescent bulb works, with an element heated to around 2700K, which explains their warm color. The most common color temperatures available are as follows:
2700K warm white is recommended for most household use as it is close to the bulbs that people are used to.
3000K is still classified as warm white, but is slightly colder than 2700K and mimics a halogen lamp. Therefore 3000K fluorescent tubes are often used in kitchens which are decorated in white or silver metallic to give a clean feel.
4000K is a cool white that is often used in office buildings, and you might consider it for a home office to give a more professional feel.
5400K lamps are often branded as "daylight" colored, having a similar quality of light to a hot summer's day with a blue sky. This is a very cold light that would not usually be used in the home, but may be helpful for people with Seasonal Affective Disorder.
6500K lamps give off a slightly harsh bluish-white light, and are generally used by people such as architects to make drawings on white paper appear very clear.
Color Rendering Index (CRI)
This is basically a measure of how realistic colours look when they are lit by a lamp. A standard incandescent bulb scores 100% as it produces the full spectrum of colors and therefore has perfect color rendering. Fluorescent lamps have a lower CRI because they do not produce the full spectrum of light. Good quality "triphosphor" fluorescents use three phosphors to give off red, green and blue light. This tricks your eyes into thinking they are seeing white, in much the same way as a TV screen works. If you want colors to look good, you need to choose a fluorescent lamp with a CRI of 80% or higher. This will be fine for everyday use. Specialist fluorescents are available with a CRI higher than 90%, but these are slightly less efficient and are usually only used by professionals such as graphic designers or artists.
You should avoid buying tubes for the home if they do not have a CRI rating of at least 80%, as they may be cheap tubes intended for office buildings. These only use a single phosphor that leaves large gaps in the spectrum of light. They have a CRI as low as 50%, which tends to give people's skin a sickly look, and colors just don't look right. These give energy saver bulbs a bad name, but are greatly out-performed by modern, household fluorescents with a high CRI.
Figure 2: Color Codes
To help you choose fluorescent energy saver light bulbs, the manufacturers often use a simple, three digit code as seen in Figure 2. The first digit is the Color Rendering Index in marks out of 10. The second two digits are the Color Temperature, expressed in hundreds of Kelvins. For household use, you should always look for a CRI of 80% or more, so the code should start with the number 8. A color temperature of 2700K (warm white) would be represented by 27. Therefore, for normal household use, you would usually buy a lamp with a code of 827. For a modernistic kitchen, you might prefer 830 lamps, for a cooler, cleaner ambience.
After reading this, you should understand that there are many types of fluorescent energy saver lamps available. You should choose those which are designed for household use, and avoid the cheaper types which would be better suited to lighting your garage or workshop. Stick to 2700K or 827 coded bulbs, and you should be able to switch seamlessly to energy efficient light in your home, saving electricity and money. You should be aware that the different characteristics of fluorescent light can seem strange at first, and family members may claim to hate the new bulbs. However, the human brain adapts quickly, so after a few days they won't notice the difference, especially if you use 2700K bulbs that mimic the color of standard incandescents, but use up to 80% less energy.