You already know that the type of light falling on your hair affects the color that your hair appears to be, and you've probably noticed that the lighter the color of your hair, the more influence different lighting types have on your color. You may also know that light has a "color" temperature. Sunlight is considered "natural" light and is our reference point for all other types of light. The color temperature of sunlight at midday is about 5500 degrees Kelvin (K). Even the color of sunlight can swing dramatically based on time of day and atmospheric conditions. Whether a light appears "warmer" or "cooler" than natural sunlight depends on whether it's color temperature is above or below that of sunlight. The Kelvin scale was started in the late 1800s, when the British physicist William Kelvin heated a block of carbon to produce a range of different glowing colors at different temperatures. The black cube produced a dim red light that turned a brighter yellow as the temperature went up, and eventually produced a bright blue-white glow at the highest temperatures. In his honor, color temperatures are measured in degrees Kelvin, which are a variation on Centigrade degrees. Instead of starting at the temperature water freezes, the Kelvin scale starts at "absolute zero," which is -273 Centigrade. (Subtract 273 from a Kelvin temperature, and you get the equivalent in Centigrade.) However, the color temperatures attributed to different types of lights are correlated based on visible colors matching a standard black body, and are not the actual temperature at which a filament burns. How's that for more than you ever wanted to know about degrees Kelvin? In general, the higher the color temperature, the more "cool" or blue the light appears. The lower the color temperature, the "warmer" or more yellow the light appears. The temperature of the light in our salon depends on time of day, but ranges between 3200 and 5500 K. During the day, the light is usually around 5000 K; made up from sunlight at around 5500 K, and a lessor amount of quartz halogen, which is about 3200 K. In the evening when the sun goes down, the light in the salon is around 3200 K, a bit more "warm" looking than midday sun. If you get your color done in the salon at night and then look at that color outside in daylight the next day, your color is going to look just a little bit "cooler" outside. If you get your hair done here in the day under lighting that is about 5000 K and then go to your office, which is lit by fluorescent bulbs at around 6300K, your hair is going to look "cooler" in the office. If on the other hand, you get your hair done here during the day under lighting that is about 5000K and look at it at home under incandescent lighting at around 2600K, your hair will look considerably "warmer" or more golden at home. Household incandescent light is one of the "warmest" or yellowest artificial lighting sources you are likely to encounter other than candles or a fireplace. You can purchase bulbs to achieve just about any color temperature you may want in the rooms of your house.

The chart below illustrates the range of lighting in degrees Kelvin.

Skylight (blue sky) 12,000K - 20,000K

Average summer shade 8000K

Light summer shade 7100K Typical summer light (sun + sky) 6500K

Daylight fluorescent 6300K

Overcast sky 6000K

Clear mercury lamp 5900K

Sunlight (noon, summer, mid-latitudes) 5400K

Design white fluorescent 5200K

Special fluorescents used for color evaluation 5000K

Daylight photoflood 4800 - 5000K

Sunlight (early morning and late afternoon) 4300K

Brite White Deluxe Mercury lamp 4000K Sunlight (1 hour after dawn) 3500K

Cool white fluorescent 3400K

Photoflood 3400K

Professional tungsten photographic lights 3200K 100-watt tungsten halogen 3000K

Deluxe Warm White fluorescent 2950K 100-watt

incandescent 2870K 40-watt incandescent 2500K

High-pressure sodium light 2100K

Sunlight (sunrise or sunset) 2000K

Candle flame 1850K - 1900K

Match flame 1700K

So the moral of this story is; if you're really particular about the color hue of your hair, take into consideration where you want it to appear ideal. Out at night with lots of warm, yellow lights typical of clubs and people's houses? Or in an office environment that may have much cooler lighting? Or in the sun? The difference isn't huge, but there is a difference.