Oh no,not another LED lighting question...........

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ian
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Oh no,not another LED lighting question...........

Post by ian »

Got a BIG BIG sign, translucent red, lit from behind by fluorescent lamps.
Maybe 20 10' letters in it.

Now I'm thinking, due to thier characteristics in this application, Leds could
really outdo even efficient fluorescents.

Consider that fluorescents light 360 degrees, so a lot of light is lost towards
the back rather than lighting the sign.

Also, since it's a RED sign, a lot of the fluorescent's light is blocked by the
red translucent material.

In addition, RED leds are directional, cheaper, and brighter than most other colours.

I'm trying to get clear numbers on this, but OHHHHHHHHHHH the web hype!

Anybody got good info on how much light a fluorescent actually supplies
in this configuration? How much light might be blocked by the translucent
material?
Maybe some kind of factor as to how many lumens a fluorescent would need
as opposed to leds for the same brightness?
The best kind of LEDs (brightest bang for th buck) for this?

It's a big deep sign so I can set the leds far back inside the sign to evenly distribute
the lumens for an evenly lit sign.

I'm trying to figure out a clear business case from maintenance, to brightness,
to energy savings, to environmental advantages.
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Joseph
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Re: Oh no,not another LED lighting question...........

Post by Joseph »

My rough impression is that it sounds like a good idea. I am pretty sure that it will take more than a few hundred LEDs, maybe a few thousand, even. I'm not getting a clear impression because LEDs are usually specified in candelas and fluorescent bulbs in watts or lumens. From what I pick up from Wikipedia, the light emitted by fluorescents that does not fall on the letters won't be lost in the calculation in comparison to LEDs. That is, the way candelas and lumens are calculated means the more directional the LED is, the lower its lumen rating for a given brightness as seen within its light cone.
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dacflyer
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Re: Oh no,not another LED lighting question...........

Post by dacflyer »

i'd tend to think that all them thousands of leds might use more power than the fluorescent lamps. not to mention the cost of all the leds and power supplies
gerty
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Re: Oh no,not another LED lighting question...........

Post by gerty »

Have you given any thought to conforming to the shape of the lettering with strip leds like this
http://superbrightleds.com/light_bars.htm
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CeaSaR
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Re: Oh no,not another LED lighting question...........

Post by CeaSaR »

Dac,

I was going to comment on the price issue also, but you beat me to it. Let's not forget the time spent
building just one display, let alone making it a "business". I would think that the ROI on something like
that would be in the medium 10's of years, where you can't even factor in the repair time that would
inevitably be needed. Conventional signs would only need a basic set of handtools to fix, while you would
almost have to take such a large sign to a shop to fix a problem. Not sure if such a large sign would be a
good thing with all LED's, especially when flourescents are as mature and reliable as they are. Not to mention
relatively inexpensive to replace completely.

Just my take,

CeaSaR

P.S. I have seen the LED TV signs along the roads, but they are relatively new so I don't have an opinion on
their reliability. I'll just have to wait and see.
Hey, what do I know?
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haklesup
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Re: Oh no,not another LED lighting question...........

Post by haklesup »

YOu could get away with a far fewer number of high brightness LEDs. Their higher cost would be offset by not needing hundreds to thousands of them. The HB LEDs though will need some heat sinking and ideally a driver IC and no matter what, the power supply will need to be fairly high current which will make it expensive. It's possible but will take some careful consideration of the BOM to make it cost effective.

An outdoor lighted sign on a hot summer day can be like a greenhouse for those LEDs. You'll probably want a ventilation fan so you don't prematurely kill the lamps. Just another thing to service and have fail. Again, possible but you would want to engineer every aspect of the sign, not just design it with familar part numbers. You need to do a lot of research selecting the right LEDs and substrates to mount them on.

Its certainly possible. Scrolling LED signs have been around for quite a while, just visit times square to see some
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dacflyer
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Re: Oh no,not another LED lighting question...........

Post by dacflyer »

now a lot of smaller signs with channel lettering is being replaced with leds, it is popular as a neon replacement in channel letters as well.
especially since neon is not cheap and it can be dangerous with its HV anywhere from 2,000 - 15,000 volts @ 30ma - 60ma for colder climates.
i used to make and deal with neon and sometimes it could be a real bugger to make it fit and connect into the channel letters,
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