Fillable Printable Understanding Lighting Colors and Light Output

Understanding Lighting Colors and Light Output

"Warm," Cool," Daylight," etc.

Yellowish white light, reminding people of a fireplace, is called "warm" while bluish white light is

called "cool." These are based on associations with these colors. "Daylight" is supposed to

mimic light coming in from a window. These are crude, but useful classifications. However, we

can have differing degrees of "cool" and "warm": and therefore we need a quantitative measure,

the Correlated Color Temperature, described below.

Correlated Color Temperature (CCT) measured in Kelvins (K)

Correlated Color Temperature (measured in Kelvins)-or simply Color Temperature-is a scientific

scale to describe how "warm" or how "cool" the light source is. It is based on the color of light

emitted by an incandescent source. As a piece of metal (a theoretical Blackbody) is heated, it

changes color from reddish to orange to yellowish to white to bluish-white. The color of light

emitted by an incandescent object depends only on the temperature. We can use this scale to

describe the color of a light source by its "Color Temperature."

When we say a lamp has a Color Temperature of 3000 Kelvins, it means a glowing metal at

3000 Kelvins would produce light of about the same color as the lamp. Instead, if the metal is

heated to 4100 Kelvins, it will produce a much whiter light. Direct sunlight corresponds to about

5300 Kelvins while daylight, which has the blue from the sky mixed in, is typically 6000 Kelvins

or above. A standard incandescent lamp has a filament at 2700 Kelvins, and therefore (by

definition) a Color Temperature of 2700 Kelvins.

Lumens Vs. Watts Output

We often tend to think of a light bulb's brightness in terms of watts, because we have used the

same kind of bulb---incandescent---for more than a century. But this is misleading. Watts

measure the amount of electrical power that a light bulb consumes, but do not directly indicate

the brightness of the light that the bulb emits. Brightness is in fact measured in lumens

Why It Matters

As new types of bulbs move onto the market, it becomes more and more important

to base buying decisions on output in lumens rather than energy consumption in

watts. Fortunately, though, we can expect that as long as traditional incandescent

bulbs remain available, marketers will continue to describe the light output of other

kinds of bulb, such as compact fluorescents and LEDs, in terms of the light

produced by an incandescent bulb of a particular wattage.

What is a Watt?

A watt is a unit of power. According to Dictionary.com, it is "equivalent to one joule

per second and equal to the power in a circuit in which a current of one ampere

flows across a potential difference of one volt." In layman's terms, a watt is the

result of multiplying amperes by volts. In the case of electric light, it is the amount

of power used in one hour by the bulb. A 100 watt bulb uses 100 watts of power

every hour it is on, a 60 watt bulb uses 60 watts, and so on.

What is a Lumen?

The rating of a bulb in lumens tells you, quite simply, how bright it is. The PC

Magazine Encyclopedia states that "Lumens define 'luminous flux,' which is energy

within the range of frequencies we perceive as light."

Lumens and Watts

Most of us are so used to thinking of bulb brightness in terms of watts that we

forget that this only works when we're talking about the same kind of bulb. A

traditional 75 watt incandescent bulb will always be brighter than a 40 watt bulb.

But an18 to 25 watt compact fluorescent can deliver the same brightness (1,100

lumens) as a 75 watt incandescent bulb---making it much cheaper to use.

The Marketplace

To conserve energy, U.S and a number of European countries have banned or will

soon ban incandescent bulbs from domestic use, in favor of compact fluorescent

bulbs. This is because, as we've seen, compact fluorescents produce more

lumens per watt---in other words they are more efficient. LED bulbs are an even

more efficient technology. As these new products push aside traditional

incandescent bulbs, consumers will find it increasingly useful to think in lumens

rather than watts.