blue neon light

[Dave Stanton]

PC World, OH DEAR, no I don't expect they would have a clue. Try

( I think)

Dave

[Dave Stanton]

You can also try

And very soon Micro Mart will be doing an article on this very subject. You can Micro Mart from W H Smith.

Dave

[geoff]

Or amalgam fillings

[Fraser]

And they are common as muck these days. Blue LEDs were cool, until folk started putting them on cars!

The rope stuff linked by Paul is probably your best bet. I've not seen it on Fiestas or Civics yet, so it's therefore still cool.

F./

[Martin Angove]

Maplins do 'em too. Try pages 297 to 299 in the paper catalogue, or order codes such as A93AH, A89AK, A90AK online. A64AL is quite groovy. Of course, these are all designed to run from a PC powersupply, probably

12V or maybe 5V.

Also available in the hobbies section p612 N50AN includes a 12V supply. Ten quid each for a 30cm tube... almost worth dusting off the blow-torch and having a go at bending the tube yourself :-)

Hwyl!

M.

[Daniel]

Firstly, thank you for all the ideas. And the general lack of sarcasm which was very surprising!

I looked at this - my worry is that it would not give out enough light. In order for it shine through the glass block wall, you need a fair amount of light.

On reflection, I feel the cat idea was a pretty useless one (!) and am now tempted by the ultra-bright led lights recomended (luxeon ones).

In simple terms how would I go about hooking these up to mains electricity? I will be powering them off mains, not the lighting circuit.

Do I need a professional?

Daniel

[Dave Plowman]

LEDs work off DC, so need a DC supply usually provided by a transformer and rectifier. They are current rather than voltage sensitive, so a suitable series resistor is needed according to the voltage driving them. For example an LED driven at 10 mA which is common for 'indicator' types would need a 1000 ohm resistor when run off 12 volts. Brighter LEDs will need more current and therefore a smaller value resistor at the same voltage. Obviously, if you're using a lot of these, the higher the voltage the smaller and cheaper the power supply as the current is less, so 50 volts might be the best - but 50 volt wall warts etc aren't common.

Maplin do an 0.8A 12 volt unregulated wall wart for 9.99. This would drive about 30 reasonably bright LEDs at around 25mA each. Would 30 be enough?

It would, of course, be pretty easy to make a low voltage PS of near any current using bits from Maplin or similar. It all really depends on how much work you want to do, and your competence at DIY electronics.

It is possible to drive LEDs directly off the mains, but making such an arrangement safe for this application would, I'd say, be too complicated.

Ebay can be a good source of cheap LEDs. Look under Electronic Components.

[Tim Mitchell]

In article , Dave Plowman writes

Umm. The above is partly true for standard LEDs, except that the forward voltage drop of the LED is fixed, so using a higher voltage supply does not help, unless you start series connecting the LEDs. Also for blue leds the forward voltage drop is quite high (about 4 volts) which you need to remember when working out the resistor value.

The Luxeon ones previously mentioned are very picky about supply. You need a current limited supply feeding 300mA to each LED. You also need to provide cooling for the LED devices or the lifespan is greatly reduced. I think you would need to get an expert involved if you wanted to do it, it's not rocket science, but you do need a bit of electronic design knowledge.

[Simon Avery]

Hello The

This was explained recently on a kiddies program in a way that even I kinda got the idea - it /is/ Neon. What happens is that Neon also emits shedloads of ultra violet light. To get different colours, the inside of the tube is coated with pigments that react in different colours when energised by ultraviolet.

So the neon creates ultraviolet. The UV transfers energy to the coating. Coating glows and emits colour of choice.

[Tim Mitchell]

I don't think that's true about neon gas, neon just emits red.

If they want other colours they use [some other gas - mercury vapour?] in the tube to make the uv and then add a fluorescent coating as described.

Normal white fluorescent tubes work that way as well.

[Grunff]

Hi Simon,

There are actually two types of blue tubes, those which have a phosphor coating, and those which don't.

Tubes with a phosphor coating work in almost the way you describe (as do common-or-garden fluorescents). I say almost because while the fill is almost entirely neon, neon doesn't emit much UV at all, it's the trace mercury content which does that.

These tubes can be identified by the fact that they are opaque - due to the phosphor coating.

The second type are clear, because they're just glass tubes with argon in them. These emit blue light which is emitted directly by the argon fill, with no phosphor being involved.

[Andrew Gabriel]

Mixed with the directly visible neon emission.

It's got lots of lines, and certainly into the UV. It is used for exciting UV phosphors, although the UV won't get through ordinary glass construction neon lamps.

Mercury vapour has the problem that the vapour pressure varies enormously with temperature, affecting both the light output and the electrical characteristics. This isn't much use in cold-cathode signage tubes which need to work well when cold and the mercury vapour pressure is too low, or if increased for cold working, it's too high if the tube warms up.

Older tubes are designed to work at 25C ambient with bulb wall at

40C and get dimmer if you move away from this in either direction. (They can be made to order for different operating temperatures.) Newer tubes, particularly compact fluorescents, contain an amalgam which absorbs and releases mercury depending on its temperature and this stablises the mercury vapour pressure inside the tube for varying lamp temperatures, at least over a wider range than for older fluorescent tubes. There is a delay whilst the amalgam pellet adjusts to varying temperatures (which is why compact fluorescents take a minute or so to reach full output).

This is fine for lamps which are on continuously, but not for neon signage which often isn't, and has to run at exposed outdoor temperatures.

[Dave Plowman]

But neon tubes are clear glass? Sure you're not confusing them with fluorescent tubes?

[Martin Angove]

That's interesting, because at Magna we had bottles of Argon as used by signage designers, mounted in a case, with 22kV (or something) clunked onto each end when people walked past.

The "sparks" inside were definitely mauvey - I'd say more towards the orange than the blue :-)

Hmmm...

Hwyl!

M.

[The Natural Philosopher]

I think not actually. In the USA any fluorescent light is called a 'neon' light, and what you have descrbed is what we call fluorescent lights. They are normally filled with mercuty vapiour and an inert halodegn as well - I think argon normally. The tubes are caietd with phosphors to re-emit UV in the visible spectrum.

Traditionally what WE call a 'neon light' is a pure discharge tube - not a coated one - of which the original ones were red/orange and contained neon. The sort used to make advertising signs. I don't know what gasess are in the red, blue green and yellow ones, but I am pretty sure it ain't neon.

[The Natural Philosopher]

Thanks. I knew it wsn't neon, but for the life of me...nonetheless all such (direct emitting) tubes in the UK are comonly called 'neon' lights. As opposed to 'fluoreescent lights', which of course in the USA are called 'neon lights'

[The Natural Philosopher]

Exacrly. Each gas has a characteristic spectrum, as described by Fraunhofer: The color ypu preceive from a direct gas dicsharge lamp depends on where te spectral lines are and how string they are. Neon is predomniantly a red/orange emitter, with negligible UV, other inert gases are different. By combining them you can get a variety of colors. I suspect this is in fact what sign makers do.