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Is this accurate about LED's ??
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| jeeper2269 Regular  Joined: 28 Aug 2005 Posts: 277 Location: Oregon |
The thing I am wondering is if agencies have seen problems with certain types of LED Lightbars, as described by the insider. I would hate to go ahead and spend the money for this raved technology and find out in a couple of years that they are getting dimmer, and dimmer.. One, other question, has anyone used the Whelen Liberty or Patriot Bar in an area with large amounts of snowfall? If so, did you have any problems? thanks |
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New member
Joined: 12 Nov 2005
Posts: 5
Location: Just south of Buffalo, NY
 Posted: Sun 13-Nov-2005 08:52 Post subject: |
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We have at our Fire Company a liberty bar with corner strobes, center led and rear led arrow. It is on our Chief's vehicle now for two years and we have not noticed any degradation of the lighting. We have a 72 inch whelen bar maybe the patriot but i'm not sure, it is on our second due engine and it has been in service for nearly 3 yrs and again no degradation. The only led lights we had a problem with is our 911Ep bar we have on the rear of our ambulance. For some reason or another a couple of the lightheads would quit. This happened twice to two different bars and both times the same lightheads. I am happy to say that 911EP did replace the bars we had trouble with and the one we have now has been working fine.  Hope this helps. |
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Regular
Joined: 28 Aug 2005
Posts: 277
Location: Oregon
| Posted: Sun 13-Nov-2005 09:07 Post subject: thanks |
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| helps a lot. We were actually also looking at placing a 911EP TA strip on the back of the new tahoes between the bumper and the liftgate, but decided not to due to the snow build up on rough winter days. we also figured one of the officers would bump the strip while getting in and out of the back and damage the bar. I believe we will go with hideaway strobes in the rear reverse light housing with our existing halogen arrow stick in the rear window, with Single Talons on each side of the Stick,, red and blue. | |
Regular
Joined: 22 Oct 2005
Posts: 97
Location: FG, Oregon
| Posted: Sun 13-Nov-2005 13:58 Post subject: |
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| Jeeper where in Oregon are you? | |
Regular
Joined: 28 Aug 2005
Posts: 277
Location: Oregon
| Posted: Sun 13-Nov-2005 14:37 Post subject: Location |
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| Central Oregon, Bend Area.. looks like you are from forest grove? | |
Frequent Poster
Joined: 29 Aug 2005
Posts: 1196
Location: Victoria, BC, Canada
| Posted: Sun 13-Nov-2005 18:31 Post subject: |
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| Jeeper,
Ok - here's the long story.... The heat issue described above is a massive issue for LEDs. Heat left in the LEDs (i.e. - not removed by heatsinks) causes 3 things to happen; - decrease in light intensity (sometimes up to 40% in 20 mins) - colour shift (blues turn aqua, reds turn pinkish) - increased power draw in some situations Decreased Light output As soon as the LED is turned on, the intensity starts to decrease. This is true of any Gen III LED, regardless of the manufacturer of the light module (FedSig, Whelen, etc.). However, the initial drop is usually slight enough that you don't notice it without a meter. After 15-30 mins, as the light warms up, is the important part. Without a heat sink, you can lose 40% of your light output. A 'snappy' light now just looks fairly bright, or even worse. Once the lights cool, they'll regain their brightness when turned on again. Colour shift (yes, I'm Canadian) Another major problem with heat is colour changes. Again, not a problem when the bar initially fires up, but when it heats up you'll notice a change, particularly in reds and blues. The blues turn a kind of aqua, for example. Amber isn't so noticable. Putting LEDs behind a coloured lens (an exterior dome) can decrease the light output of the lightbar. If a red LED is behind a red dome, then the colour red shifts to pinkish, the red dome (which only lets through *red* light, not pink) filters out the pink colour and then the overall light output drops dramatically. Since all LEDs shift colour to some extent, putting them behind clear domes is always best. Increased power draw Depending on how the LEDs are powered (ballast-type or passive regulator), the hotter the LEDs get, the more power they require. This is a vicious cycle; get hot, draw more, which makes them get hotter, then they draw more, etc. This is known as \"thermal runaway\". Nasty, but most manufacturers have controlled that now. The other way to get increased power (and you can try this if you have any 'ballast' type LEDs), is to decrease the voltage. If, on a ballast-type LED light, you reduce the input voltage (from 13.8 to say...11.5v), then the amp draw increases. It can be very significant in many cases. Even Code3 warns you in it's literature to fuse your bar for 1.5a per module, when the 'rated draw' is only .75a per module. I've heard stories of early Code3 bars melting their ballast power supply during very low-voltage tests. The bars' power draw increased so much that the internal LED power supply had too much current going through it and melted down. Now, many bars still using this ballast-type system have a low-voltage shutdown that turns the bar off when the battery voltage drops too low. Take your ballast-type LED module, and power it at 13.8v ( a normal car's voltage when the car is running). Measure the amp draw. Then, drop the input voltage and keep measuring the amp draw. It'll increase. This is a nasty surprise, as when your car is in a low voltage state and needs all the help it can get (in terms of lessening the loads on it), the LEDs actually draw MORE power, causing the battery to die faster, etc. Another vicious cycle. This is not the case with 'passive' systems - they draw LESS power as the voltage drops. The downside is that passive LED's light output drops a bit as the input voltage drops. Ballast type systems also have very nasty radio frequency interference (RFI). The lesson; - Always evaluate LEDs (brightness and colour) after they've been on for at least 20-30 minutes, and - shy away from ballast-powered LED systems if you care about a) amp draw and b) radio freq. interference Hope this helps M |
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