Tuesday, August 7, 2012

The Future's so bright: Issues with "bright" LEDs for EMCs


-Deacon Wardlow
NITs, Lumens, Flux, Foot Candles*, however light output is tested you have to be sure the reported measurement is giving you the complete story. The output on your EMC (Electronic Message Center) may not be what you think it is. Overdriving LEDs still occurs in the industry because people believe brighter is better. When you look at the brightness rating on a system, be sure you get what you’re paying for.

The practice of overdriving LEDs has been around as long as LEDs themselves. An LED has a given rating for performance. Go under the rating for an LED and you’ll have mid to fair performance. At optimal rated driving (current passed through the LED) an LED will shine its brightest for the longest measure of time before it depreciates below useful levels. When someone overdrives the LED, they cause more current to flow through the LED.

LEDs work via PWM (pulse width modulation). The faster an LED pulses, the brighter it appears. The slower the pulse, the dimmer the LED appears. By increasing current to the LED, it’s overdriven and made to appear/test at higher levels than normal.

More current = more/brighter pulses = brighter LEDs. Unfortunately more current = more heat = faster degradation of the LED = shorter lifespan for the LED sign. Here’s a short example of the Overdrive factor and how much the lifespan of an LED is reduced:




While a manufacturer may claim higher brightness, be wary on how they obtain that brightness. If in doubt, ask them to name the manufacturer of the LED and go direct to the LED manufacturer to check brightness capability claims. A reputable manufacturer should be able to show proof the LEDs are all within rated ranges and not being overdriven and they should have no qualms with you verifying the information yourself. Don’t let claims of high brightness on an EMC blind you to the truth.

*For a deeper description of the abbreviations and terms, please check the online EMC glossary here.If you like it, please drop a thank you email to me (and the team at Vantage LED) for the info! Also read about NIT Values and Measurements here.


**Always feel free to comment here and/or email me directly with requests at deacon@vantageled.com. Vantage LED has white paper resources and more educational material on the website (http://www.vantageled.com), please check it out when you have a moment.

***Note all posts/thoughts/writings are strictly the viewpoint of me and me alone and do not reflect nor speak for Vantage LED’s beliefs, attitudes, thoughts, etc. unless specifically stated.

2 comments:

Ivy Feng said...

Hey Deacon, thank you for sharing the info. PWM usually requires better choice for diving ICs, such as MBI5042. This is a relatively new driving method which increase the efficiency in LED part. Not only the brightness, PWM can also help raising the fresh rate which is also vital to video boards. Love your blog. Hope to learn more from you.

Ivy

Deacon said...

Good point! Through use of driver IC and careful LED specification, it's possible to increase brightness w/out damaging the LED (and the technology is getting better all the time). People still need to watch out for tricks some manufacturers will pull to make a poorly engineered system look good (it'll look good in the short term, but ultimately be a disappointment down the line).

I'm glad you like the blog! Thanks for commenting.

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