Lighting Information

What is light?

Light is a form of electromagnetic radiation which is visible to the human eye. It spans a spectrum from infra-red to ultra-violet. The human eye interprets the wavelength of the light as different colors.

But light is so much more than just that. It plays a vital role in our daily lives. When implemented correctly in our work environment lighting provides employee satisfaction, higher performance, comfort and importantly safety. In our leisure time it creates ambiance, provides a mood and sometimes down right dazzles.

The following sections will give you an overview of some of the key issues to determine when choosing the lighting what that is right for you. It is broken down in to product categories, general information and a full glossary of terms so next time you speak with a lighting designer or lighting consultant you will be fully armed to make the right decision.

Light & Color

Color is our eye’s way of interpreting different wavelengths in the light we see. There are three main colors of light: red, green and blue. When all three are mixed together they add to each other making white light. Combinations of these colors yield all the various we see.

When light reflects off a surface some of the wavelengths or “colors” are absorbed. Others are reflected. The ones that are reflected are picked up by our eye and we then say that apple is red or that car is blue. The surface of the apple is absorbing all of the blue and red wavelengths in the light and reflecting the green. If we shed light with only blue and red wavelengths then nothing will reflect off our apple and the apple will appear very dim.

Color Rendering

Although when we look directly at a two light sources they may have the same color appearance, it doesn’t mean that all surfaces will look the same color when illuminated by these lights. The reason is that these light sources are made up of different blends of wavelengths. Because of this difference, when viewed under different light sources an object may change is appearance. For instance a red apple will appear truly red when viewed under a white light (one that has a continuous spectrum). However when it is viewed under an equally white looking light which is actually a mixture of yellow and blue light it will look grayish brown. This color change is due to the lack of red light in second light source.

Color rendering is highly important in artificial light because it change they way we perceive objects and their colors. The ability of a light source to accurately show the colors of an object is referred to as color rendering. Natural daylight has the best color rendering. Color rendering is measured on a scale of 50-100 Ra with 100 being sunlight.

         Ra = 90-100 Excellent color rendering properties

         Ra = 80-90 Good color rendering properties

         Ra = 60-80 Moderate color rendering properties

         Ra < 60 Poor color rendering properties

For tasks where manual dexterity and attention to detail are important a high color-rendering index is ideal. In other applications such as displaying retail products a high Ra value is important as it shows the merchandise as it would appear in daylight. The colors “POP”.

A topic which has become increasingly important in light design is photopic and scotopic lumens. Photopic or design lumens represent the relative sensitivity of the eye under intense lighting such as full outdoor sun. Photopic lumen output is the amount of light registered by the cones in the human eye and is measured by standard foot-candle and lumen meters.

Scotopic lumen (also known as pupil lumens) is the sensitivity of the eye under typical interior lighting conditions. It cannot be directly measured with a standard light meter. Scotopic lumen output is the amount of light registered by the rods of the human eye and also controls pupil size directly affecting visual acuity for tasks. For lighting interior spaces a correction factor may be applied to photopic lumen readings to find the usable light produced by a given light source. For that reason you may enter a parking garage lit with high-pressure sodium lamps (CRI 23, 90 lm/w) and have trouble seeing details and many colors. This is because our eyes are only really registering 68 lm/w and having trouble identifying colors due to the extremely poor CRI.

The Lighting Systems Research Group at Lawrence Berkeley Laboratory developed a conversion factor that applies the P/S ratio to lumen output of various light sources in both photopic and scotopic lumens. Some lamps loose much of their lumen output when corrected for scotopic lumens. Others improve greatly. See the following chart for a breakdown:

The reason for the difference is that the eye is more receptive to light in the blue end of the spectrum. Cooler temperatures of light are more common in natural light so our eye has evolved this way. The importance of taking into account the scotopic lumens when choosing an appropriate light source is clearly evident.

Color Temperature

Since all white light is made up of a combination of additive colors white light can differ slightly. White light with more of the red spectrum will appear warmer while white with a higher proportion of blue will appear cooler. To classify the different types of white light a black body is heated until it gives off light. The color of light emitted at a specific temperature gives us the scale. An example is the filament of an incandescent bulb. When heated to 1000k it will appear red. Between 2000k-3000k the filament will look yellow white. Raise the temperature to 4000k the white becomes more neutral. Finally as it approaches 5000-7000k it appears very white almost blue.

Different light sources have traditionally given off different color temperatures of light. Many of us remember the first Compact Fluorescent Light (CFL) we saw. It was very blue looking. Now fluorescent lamps are made in a large variety of color temperatures. Below is a chart that outlines the color temperatures of carious light sources:

When choosing what lighting to bring into your space it is important to consider what color temperature to use. Here are some considerations to evaluate:

Color scheme in the interior – if your interior has colors containing mainly red (orange, yellow, purple) a warm light (lower color temperature) will be preferred. If the colors are more in the blue spectrum a cooler (higher color temperature) light is ideal.

Ambiance: warmer (lower) color temperatures create a cozy and inviting atmosphere. Restaurants and more dimly lit spaces benefit from this warmth. A cooler (higher) color temperature is better for business or formal settings such as offices and institutional spaces.

Climate: colder climates prefer warmer light while inhabitants of warmer climates prefer cooler color temperatures.

Level of illumination: since we intuitively take daylight as a reference our senses naturally assume that dimmer light should be warmer, just like the setting or rising sun. Brighter light is correlated with daytime color temperatures and therefore higher levels of illumination should be lit with a cooler color temperature.

Photometrics

There are four basic and essential photometric units that lighting designers and consultants utilize to measure light:

1. Luminous flux: the total quantity of light radiated per second by a light source. Luminous flux is measured in lumens (lm). Examples:

     75w incandescent lamp:                                       900 lm
     39w fluorescent lamp:                                        3,500 lm
     250w high pressure sodium lamp:                   30,000 lm
     2000w metal halide lamp:                               200,000 lm

Flux is of great importance when designing general or area lighting.

2. Luminous intensity: the flux of light emitted in a certain direction. Luminous intensity is measured in candela (cod). Examples at centre of beam:

     5w bicycle lamp without reflector:                          2.5 cd
     5w bicycle lamp with reflector                               250 cd
     120 incandescent reflector lamp                      10,000 cd
     Lighthouse                                                   2,000,000 cd

3. Luminance: the light emitted from a unit of area in a specific direction, Luminance is expressed in cd/m2. Examples:

     Filament of a clear incandescent lamp:      7,000,000 cd/m2
     Fluorescent T-8 lamp:                            5,000-15,000 cd/m2
     Road surface under artificial lighting:                 0.5-2 cd/m2
     Surface of the Sun:                              1,650,000,000 cd/m2

4. Illuminance: the quantity of light falling on a unit area of a surface. The unit of illuminance is lumen/m2 or lux. Examples:

     Full moon, on a clear night:                                         .25 lux
     In the open under a heavily overcast sky                     5,000 lux
     Artificial T-8 light in an office                                         800 lux
     Summer, at noon, under clear sky                            100,000 lux

Illuminance is the most commonly measured aspect of lighting when designing or retrofit is being completed. It is measured using a photometer.

Choosing the Right Light

With the incredible variety in lighting technology to choose from it is often difficult to determine what is the best lamp and fixture combination to choose. While this is a science which has been studied for decades and continues to grow there are some basic ideas to keep in mind.

Lighting Level

The amount of light we have to operate in when performing greatly affects our ability to perform that task. The lighting level must always be high enough to allow sufficient visual acuity to perform the required task. Research has proven that increasing lighting level can greatly increase the speed and accuracy with which objects can be detected and recognized. In a work environment visual performance depends not only on the quality and quantity of lighting but also on the persons own visual abilities. Older people require much brighter conditions. For instance a 60 year old requires 15 times more light than a 10 year old to complete the same visual task as a 10 year old. Tasks which demand fine details or rapid recognition require more light than basic tasks or slow recognition. For instance you would want much brighter conditions for playing squash indoors than moving boxes in a warehouse. The speed and size of the objects you are using allows for a lower lighting level in the warehouse application. For an excellent overview of what lighting levels to use consult the IESNA standards for illuminance.

Contrast

When lighting a space it is important to consider how you would like different areas to contrast against one another. If the luminance contrast is too high the space will be distracting. If it is too low there will be no points of interest. A general rule for indoor situations is that the area should have no area 3 times lighter than another.

Glare

Glare occurs when we look at an object that is reflecting light considerably greater than the brightness which our eye is adapted. We have all experienced the challenges of glare and how it can greatly hamper our ability to see and function. Point source lamps such as HID, incandescent and halogen lamps product significant amounts of glare and therefore should be shielded in certain applications. Linear fluorescent and CFL lights tend to produce least glare.

Distribution of the light

Not only the type of light selected but where it is placed within your space is of utmost importance. Lighting designers, lighting consultants and architects’ provide expertise in this area however much can be done by logically looking at your space. Spreading the lighting sources evenly through a space allows for a gentle and even feel. Specific, directional lighting creates more contrast and effect. Combining general and direct lighting often creates the ideal situation.

Color Rendering and Temperature

Choosing lights with higher CRI makes it far easier for those using a space to see details and colors accurately. Any application where attention to detail or rapid recognition is necessary demands a CRI of at least 80 Ra. Choosing the correct color temperature is also essential as it can greatly affect the mood and feel of a space. For calmer spaces choose a warmer color temperature (2500 – 3200k). Applications such as restaurants, homes, spas and hotels benefit greatly from the warmer color temperatures. For spaces such as offices, warehouses and institutional spaces having a cooler temperature is much preferred (3500-6000k). The cooler temperature increases alertness and makes the situation more formal.