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Topic: Neon and Argon/mercury cold cathode tubes.

Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 04-18-2011 02:57 PM

Anybody have any experience with these? I have a 40 mA low Voltage (980 V) transformer; how much 12 or 15 mm tubing could I drive with this? I want to use it with two lengths of tubing, so four electrodes in total. I'm hoping to use tubes each about 700 mm long, plus the turned back section of about 70 mm at each end to the electrodes, so about 1.68 metres of tube in total. Does the diameter of the tubing affect the length which can be driven at a given Voltage? I'm assuming that a short length of HT cable, about 1.5 m in total, from the transformer and between the tubes, won't make any difference.

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 04-18-2011 03:27 PM

Stephen, check out this link:

Franceformer loading chart pdf

It has the info you seek.

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Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 04-18-2011 06:34 PM

Tony,

Thank you for that, there's some interesting and useful information there, but it doesn't answer the length problem, partly because it deals only with high frequency supplies rather than conventional transformers, and also because it deals only with high-Voltage.

I'm not sure what effect, if any, using a high frequency would have on the maximum tube. If length is proportional to Voltage, which I think it is for this type of discharge, then the length which I'm looking at would be close to the limit with 980V low Voltage. If the tubing was in a single length it would probably work,but with two tubes is series, with two extra electrodes in the circuit it might be too much.

I have to use two separate tubes as one needs to be deep red, neon in ruby red clear glass, and the other an intense white, argon/mercury in white phosphor coated glass. Neon has a greater Voltage drop for a given length than argon/mercury has.

This is a picture of two very short lengths of tube, about a foot long, lit experimentally on the low Voltage transformer. One is neon, and the other argon/mercury, both in clear uncoated glass. I don't have any longer tubes of the right diameter to hand that I can experiment with at the moment. The two small mercury lamps are simply propping up the tubes to keep the hot ends clear of my bed which they are resting on.

One advantage of low Voltage is that there is very little risk of arcing; the longest arc you can get with this transformer is about half a mm, and in this picture the connections to the transformer are uninsulated. Low Voltage also allows the use of thinner, more flexible cable. While there's little risk of an arc I would still take care not to touch it; it can source 40 mA, which is more than I would want going through me.

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Bobby Henderson
"Ask me about Trajan."

Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001

posted 04-18-2011 07:29 PM

Stephen, here is a more detailed list from the Allanson web site.

It doesn't look like the transformer you have was specifically designed to power neon. The secondary voltage isn't high enough to power more than perhaps 4 or 5 feet of tubing. But that might be enough length for what you're wanting to do. If the transformer is fairly new it may be of the ground fault variety. If the transformer can't handle the load it will trip. The way the neon is wired can also cause the transformer to trip.

Tube diameter definitely affects the load. You can run farther lengths of neon with wide diameters (like 15mm) than you can with 12mm or 10mm. I designed an interior neon sign for a restaurant that had to use 8mm glass to accurately depict the serif typeface in the restaurant's logo. It was a bitch to get the thing wired to where the transformers wouldn't trip. 8mm glass will make a transformer work hard. Needless to say, we never drew up anything using glass that narrow again. 10mm minimum.

When neon tube lengths get particularly long it becomes a greater issue of just protecting the glass from leaking or breaking. Border neon is pretty easy. Neon bent to the shape of letters or graphics is another matter. Often there may be one or more welds in the glass. The longer the glass unit the greater chance there is of having a leak or a weakness in a bend that causes the unit to break. More complex neon tubes (colored glass, coated glass, double coated glass, etc.) bring in more potential issues. Clear pumped blue (argon) or pumped red (neon) is the easiest.

LEDs are quickly replacing neon in a lot of border lighting situations. But there really is no substitute for neon when it comes to things like channel letters with exposed glass tubes. Only old fashioned neon can do that look.

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Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 04-19-2011 01:57 AM

quote: Bobby Henderson
It doesn't look like the transformer you have was specifically designed to power neon. The secondary voltage isn't high enough to power more than perhaps 4 or 5 feet of tubing. But that might be enough length for what you're wanting to do. If the transformer is fairly new it may be of the ground fault variety. If the transformer can't handle the load it will trip. The way the neon is wired can also cause the transformer to trip.

It's designed to power cold cathode lighting in various applications, though probably not generally for sign tubing; as you say, the Voltage would be too low in most cases. These transformers are quite common, they're available from several manufacturers, though most have a slightly higher Voltage, 990 or 995 V for example; there are advantages to using a device which is just low enough to be classed as low Voltage.

Very thin tubes of this type are used for lighting edge lit Perspex signs for example, and I've even seen slightly thicker ones used in photocopiers in the past; these sort of applications only need short tubes of course.

The transformer that I have only cost me ten pounds; it was unused surplus stock, and I think is the type which is used to light bus shelters in Derby, where the man I bought it from is based. I've seen one of the tubes which he makes for this, they're probably 20 mm in diameter, and about five feet long, bent into a 'U' shape and with the electrodes mounted straight on the tube, no need for light right to the ends of the tube, and screw terminals on the ends. They use them in this application due to the long life, but I think that they are now being replaced by conventional fluorescents when they fail.

quote: Bobby Henderson
LEDs are quickly replacing neon in a lot of border lighting situations. But there really is no substitute for neon when it comes to things like channel letters with exposed glass tubes. Only old fashioned neon can do that look.

Seems to have almost totally replaced neon in things like 'Open' signs in shop windows, and I've also seen it used in channel letters. One building which I pass on the bus going to work had some 'mock neon', LEDs in plastic tube, installed along the roof line a couple of years ago; it only lasted a few months. The shop window signs often have failed sections in them. London Bridge station on the London Underground has an area at the top of the escalators lit by downlighters which use about 50 large LEDs rather than the conventional CFL tubes; again, many of these seem to have failed, and I've not been very impressed by the very few LED streetlamps which I've seen so far. They're getting better, but I don't think they're there yet.

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Bobby Henderson
"Ask me about Trajan."

Posts: 10973
From: Lawton, OK, USA
Registered: Apr 2001

posted 04-20-2011 01:58 PM

LEDs are improving and competition is fierce in that market. Prices have lowered quite a bit for things like full color RGB electronic variable message centers and computer controlled environmental lighting. I still haven't seen a tube-like LED lighting system mimic exposed neon worth a damn. I think neon will continue to be used for many years in at least certain sign applications.

quote: Stephen Furley
They use them in this application due to the long life, but I think that they are now being replaced by conventional fluorescents when they fail.

Various factors are at work when neon lighting is replaced with fluorescent lamps. There is a perceived cost savings on maintenance by replacing neon with other light sources. Neon is fragile. However, a well made neon unit can last for many years if it isn't damaged by physical impacts or the electrodes aren't damaged by other faults in the electrical system. Here in the US tougher safety standards from Underwriters Laboratories and National Electric code have increased the costs of making and installing neon. Then there's all the various local sign codes. Some do little if anything to enforce safety standards. Others say neon needs to comply with the latest UL/NEC rules. Some communities just ban all neon signs completely out of hysterical fear any neon sign will burn down buildings.

quote: Stephen Furley
Seems to have almost totally replaced neon in things like 'Open' signs in shop windows, and I've also seen it used in channel letters.

Many channel letter signs with trim-capped acrylic faces are indeed lighted with LEDs now. LED modules can fit in much tighter spaces than neon and operate on much lower voltages. The only time I see LEDs used in exposed/open channel letters is when the entire channel letter back is covered with LEDs and the LEDs are showing computer driven graphics. That's actually pretty cool looking, but really expensive. If the exposed lighting is just doing an outline of the letter form then neon is still by far the best choice. Anything else just looks stupid.

I'm not fond of all the new LED-based "open" signs. The look is very pretentious and even cheap. But I understand why those things are being made. They cost less, can be produced in much larger quantities, are compliant with most anti-neon sign city ordinances and they don't have as many installation or maintenance issues.

Some businesses still prefer buying authentic neon for common messages like "open" or "vacancy/no vacancy". Although it will cost considerably more to have a custom neon sign made than it does to get something from a mass production outfit in China or Korea. However, the custom sign can be made from a unique design rather than something seen in many other places.

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