…LEDs, Energy Saving Marvels – Part 1…
LEDs are potentially the most important energy saving innovation in the past 50 years.
More efficient automobiles have resulted in large savings of gasoline, but these improvements have been incremental.
LEDs, while in development for at least 60 years, have only recently become available for lighting.
LED bulbs, often referred to as lamps, use far less electricity, as much as 85% less, than traditional incandescent lightbulb.
In addition, LED bulbs last for years, not hours.
LED bulbs, however, are more expensive, so it’s important to understand the science and economics behind their use.
Boxes containing LED bulbs contain three important pieces of information: Lumens, expected life, and color rendering index.
Table I, is a comparison between the wattage rating of incandescent bulbs and lumens.
|
Table I |
|
|
Incandescent bulb in watts |
Equivalent Lumens |
|
150 |
2,600 |
|
100 |
1,600 |
|
75 |
1,100 |
|
60 |
800 |
Lighting and the ability to see.
Seeing depends on the amount of light that’s on the surface of an object, which is measured in foot candles or lumens per square meter.
Standards have been established for light levels on surfaces under varying applications.
- Reading usually requires 100-foot candles on the surface of the item being read.
- Machine tool surfaces can also require 100-foot candles.
- Some precision applications require much higher levels of lighting.
The Illuminating Engineering Society has published tables showing recommended light levels for various tasks. These tables may also show required levels of light based on people’s age.
When selecting any type of lighting, it’s important to determine the amount of light that will reach the surface, which depends on the square of the distance from the light source.
Unfortunately, this information isn’t available on the box containing the lamp, and must be calculated.
For homeowners, this can be confusing. The distance from the ceiling to the working surface, such as in the kitchen, is usually about 5 or 6 feet, so it’s possible to calculate the Lumen requirements. But the calculation shows that a single 1,600 lumen bulb will only provide around 70 foot candles on the working surface, which is less than the desired 100. This means there needs to be an overlap of light from two bulbs.
Family rooms with 20 foot high ceilings pose a more complex problem.
Fortunately, lighting design firms have used the area of rooms to provide simple estimates, and they have provided these estimates for various applications on their websites.
Accurate determination of light levels can be done using a light meter.
These blanket recommendations should be adjusted for age, if the home is primarily used by the elderly.
Replica of Edison incandescent bulb and typical LED bulb that’s commercially available.
Safety is also a very important factor in lighting decisions.
A garage may only require 15 foot candles on surfaces to allow people to walk safely. Sidewalks, walkways and highways may require much higher levels of lighting to allow people to see objects in front of them or in surrounding areas.
Color rendering is the next factor to consider when selecting LED bulbs.
Esthetics may initially seem trivial, but in many situations, it is vitally important.
Different light sources produce different color readings and renderings.
|
Temperature |
Lamp |
|
1,700 K |
Sodium vapor lamps |
|
2,700 K |
Incandescent lamps |
|
5,000 K |
Daylight |
|
5,500 K |
Metal Halide |
|
7,000 K |
Cool LEDs |
The basic measurement for how light is seen is color temperature, in degrees Kelvin.
The accompanying table contains a short listing of color temperatures with examples.
Fluorescent lamps and LEDs can have a range of color temperatures. Incandescent lamps, by their nature, fall in a narrower range around 3,000 K.
Color temperatures affect how people see objects.
- Department stores are prone to use white light, with temperatures around 5,000 K, for displays. This is close to daylight, which is how people prefer seeing clothing and objects.
- Incandescent lighting typically creates a warm ambiance, which many find pleasing.
- Artists and photographers are very sensitive to how color temperatures affect their subjects. Even shadows are important, especially in portraits.
- Cities around the world appear bathed in a yellow hue from sodium vapor street lights when approached by air.
- Many cities are switching to LEDs for street lighting to save money, and have found that some LED lamps have created sleep problems for those living near the street light. It’s believed that people are more susceptible to the wavelengths of blue light and that this has created the problem, but this has not been fully confirmed.
Lumens, foot candles, (Lux in the metric system) and color rendering are the basic essentials of lighting.
- These can be affected by lamp shades, ceiling fixtures and by how the LEDs are packaged. For example, some LEDs come in flexible strips for special effects.
LEDs are the only technology currently available that can significantly reduce the amount of electricity we consume, without reducing our standard of living.
This is in contrast to entreaties to reduce consumption of electricity by eliminating some important activity, such as air-conditioning, so as to reduce our carbon foot print.
Entreaties such as this require people to do without and to sacrifice.
LEDs reduce energy usage, without the need to sacrifice anything.
Part 2 will discuss the economics of LEDs, including their rated life.
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