Vision & Sensors Exclusives

Vision & Sensors 101: The LED Basics

July 3, 2012
KEYWORDS LED
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Light output per LED has doubled about every two years since 1970. Learn more about this growing technology.



The Cree CR6 is a screw-in replacement for a 60 watt incandescent bulb and is dimmable. The CR6 requires 10.5 watts and an incandescent bulb with the same lumen rating requires 60 watts. Source: Cree


Light emitting diode applications continue their rapid rise in consumer and industrial markets. The remarkable overall growth of LEDs began decades ago and has continued into the present.


The features of two practical applications of LED illumination show why growth continues in the manufacturing environment:

machine vision illumination for on-line product, process, and quality control

broad area illumination for factory floors and other large factory areas 





Background

Increasing factory use is a partial outgrowth of the predictable and relentless growth of LED sales. Growth has been both predictable and relentless because light output per LED has doubled about every two years since 1970 (Haitz’s Law), and the cost per lumen drops as well. Dropping prices have increased the impact of light output and costs on the growth of applications and sales.

“LED lighting revenues more than tripled in three years . . . The SSL (Solid State Lighting) market almost doubled from $5.5 billion in 2010 to the 2011 level of $9.4 billion. . . The average cool-white 1 Watt LED package fell in price from $13 per kilolumen to $6 per kilolumen in one year….....” (LEDs Magazine, March 2012). This also impacts growth in other application areas of LEDs.

The growth is out in the open. It is easy to see their increasing use in cameras, LCD flat screen televisions with LEDs, computer monitors, mobile phone displays, area illumination (street, home and factory lighting), traffic lights, and automobile lights.



This LED lighting module can provide both bright-field and dark-field illumination. Source: Matrox Imaging and Advanced Illumination

Machine Vision Illumination

As you recall, LEDs are light emitting devices that use the electronic properties of semiconductors to convert electricity to light, rather than thermal emission as do incandescent light bulbs.

Semiconductor properties result in several significant advantages over competing light sources:

Lower power consumption for area illumination.

Rapid switching (turn-on/turn-off): LEDs can turn on and off in less than a microsecond (or 0.001 millisecond) for automated on-line inspection. Incandescent lights can take as long as half a second (or 500 milliseconds) for on-off switching.

This has obvious advantages in automated on-line inspection for high-volume production. First, LEDs can act as fast-acting shutters. Second, it can improve signal-to-noise ratio in defect detection and gaging, and reduce the burden on more expensive hardware.

Small size: Illumination LEDs are routinely mounted around lenses on vision cameras.

Maintenance: The lifetime of LEDs is much longer than that of alternative light sources so that the systems require less maintenance.



Broad Area Illumination for Factory Floors

In incandescent bulbs, most of the input energy is used to heat the filament, while in LEDs most of the energy is used to produce usable light (specified in lumens) for the visible-light producing LEDs.

[The Federal Trade Commission recently changed its labeling to provide the brightness in lumens, the estimated yearly energy cost assuming the given level of use and cost of power. One label states that for the same eye-sensitive output of 800 lumens, 13 watt LED bulbs require an input of only 13 watts compared to a 60 watts input for the same visible output in lumens from incandescent bulbs.]

A table providing components of cost-comparison between LEDs, CFLs and incandescent light bulbs is available at www.eartheasy.com/live_led_bulbs_comparison.html.

This table indicates that the energy savings over 50,000 hours, assuming 25 bulbs per factory or household, for using LED vs. incandescent lighting is $6,668.75. If there are 250 bulbs in use, then the savings would be $66,680. In addition, there are tax-savings incentives available: http://ase.org/resources/commercial-and-manufacturing-tax-incentives-energy-efficiency .

As if this were not enough, the semiconductor LEDs have a much longer lifetime before failure, so both hardware and labor costs for maintenance can be significantly reduced. These LED advantages have resulted in large savings in operating energy and maintenance costs and increased use.



Cost-Benefit Selection for Installing LEDs in Different Areas

The primary barrier to installing LEDs can be the initial cost of the LED units.

A simple cost-benefit consideration provides a practical way to save money and to take advantage of the relentlessly falling prices of LED units.

Simply take an inventory of where high-usage of illumination occurs, and install the LED units in these locations first. For example, if lighting on a factory floor or in personnel locker rooms is turned on for long periods of time (eight-hour shifts for one to three shifts per day), then consider installing LED illumination in these areas.

Do not install LED lighting if the locker rooms are used only at the beginning or end of work shifts. (It may be more practical to install time-switches on light switches in areas where there is limited use.)

Then, as the cost of LED lighting continues to decrease, it may be more practical to install LEDs in more areas.

This procedure has the additional benefit of providing experience with installation, use, and maintenance operations. V&S



For more information on LED illumination, visit

http://blogs.scientificamerican.com/observations/2011/01/18/the-quest-for-cool-novel-approach-leads-to-brighter-more-efficient-white-leds/

www.creeledrevolution.com/learn/anatomy

www.creeledrevolution.com/learn





Tech Tips

LEDs lower power consumption for area illumination

Rapid-switching LEDs can turn on and off in less than a microsecondfor automated on-line inspection.

With their small size, illumination LEDs are routinely mounted around lenses on vision cameras.

The lifetime of LEDs is much longer than that of alternative light sources.





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