Discharge lamps?

[maxjones2000]

Hi, I have searched this, but I partially understand it, although some of the language used was a bit confusing!

 

Basically, what is a discharge lamp? What are they used in? What are their benefits? What's 'different' about their output in comparison to normal lights (like a lamp in a parcan or fresnel)? Finally, what are their drawbacks?

 

Sorry to ask this really basic question, it's just I saw it on a previous thread and had no clue what they were on about and it made me wonder..

 

Many Thanks!

 

Max :)

[paulears]

Max - if you searched and didn't understand some of it, that's fine - but tell us what bits caused problems and we'll happily explain it - but what's the point of spending ages typing when this wiki entry covers most of it.

 

So tell us where you're stuck, and we'll help - but you have to give us a clue!

[adam2]

Advantages of discharge lamps

More efficient, very roughly 4 times the light for the same power used

Longer lasting, typicly at least 5 times longer than incandescent

Compact, the light source is smaller than an incandescent lamp of similar output and therefore more easily foccused.

Higher colour temperature is often preffered, though not always.

 

Disadvantages

Most types dont start instantly but require a few minutes warmup

Most types can not be dimmed

Dont work directly from the mains, but require control gear which adds to the cost, weight and bulk of equipment designed to use them.

 

Discharge lamps have largely replaced high power incandescent lamps for lighting buildings, roads etc. owing to the longer life and reduced power used.

For theatre lighting incandescent lamps remain very popular owing to the need for dimming, and for instant starting, and partly out of traddition.

Discharge lamps are increasingly used in theatre, mainly in moving lights. These can be dimmed, but by partialy obstructing the light, not by reducing the output of the lamp.

 

I have no doubt that high power incandescent theatre lighting will eventualy go the way of lime light, carbon arc light, and gas light, but not just yet ! there is still a lot of life in the old technology.

As well as discharge lamps, LEDs are increasingly popular, these can be dimmed (via DMX or other remote control, not normally via a standard dimmer)

Although not yet suitable for all aplications, LED lighting is improving rapidly, and discharge lamps are improving a bit.

Incandescent lighting is a mature technology and most unlikely to improve much.

[AndyJones]

I have no doubt that high power incandescent theatre lighting will eventualy go the way of lime light, carbon arc light, and gas light, but not just yet

Off topic I know, But I 100% disagree with that statement.

[Matthew Robinson]

I have no doubt that high power incandescent theatre lighting will eventualy go the way of lime light, carbon arc light, and gas light, but not just yet

Off topic I know, But I 100% disagree with that statement.

 

Why?

[maxjones2000]

Hi,

 

Thanks everyone! I Finally understand what people are talking about!! :D

 

Oh, and sorry Paul, I forgot that bit! ;)

 

My only question: If a discharge lamp is burning gas, surely doesnt it need a constant gas supply? :D .

 

Cheers

 

Max

[dave1022]

No, it doesn't need a constant supply of gas.

 

Without going into too much detail, instead of burning the gas, the lamp simply uses the gas as a medium to transfer the electrical energy put in to the light energy that is got out. That's an over simplified way of explaining http://en.wikipedia.org/wiki/Fluorescent_l...es_of_operation , which is what really happens.

[Matthew Robinson]

From that, it sounds like you need a photon to release a photon?

[dave1022]

Sorry, that link is wrong. I'll go back and edit it to a correct one. Here's how I would explain what's happening:

• There are atoms of gas floating around in the lamp
  
• There are also lots of electrons being fired around in the lamp
  
• The electrons get their kinetic energy from the electrical energy going into the lamp
  
• Whilst these electrons are flying around, they might collide with an atom
  
• When an electron collides with an atom, it bumps one of the atom electrons up to a higher energy level
  
• The electron loses some kinetic energy, equal to the energy it takes to bump an atom electron up an energy level
  
• But, the atom with an atom electron at a higher energy is unstable
  
• To become stable again the atom electron drops down to a lower energy level
  
• When it does this, a photon is emitted, which has the same energy as the atom electron loses when it goes down an energy level
  

[Matthew Robinson]

So quite similar to the flurescent tube we learnt about at AS. Ah, ok.

[madorangepanda]

So quite similar to the flurescent tube we learnt about at AS. Ah, ok.

Exactly the same in fact.

 

From the end of the first paragraph here http://en.wikipedia.org/wiki/Gas-discharge_lamp

"The fluorescent lamp is perhaps the best known gas-discharge lamp."

[Jivemaster]

The nicest feature of a discharge lamp is that the filament can't fail because there isn't one! So even when shipped out by truck between gigs the lamps will do around their published life hours.

 

The chemistry isn't readily published but a patent search may be a long way round to find the details. However Electical current passes from electrode to electrode through the fill medium. This excites the atoms which will release the energy as photons. Some lamps are single spectrum such as the yellow low pressure sodium light which uses the very bright sodium D line pair These are fantastically efficient for light output but the colour being a pure spectral yellow makes it useless for anything involving colour. Other chemistries give better approximations to white with a more continuous spectrum but most will be nearly tungsten match or near daylight or some be very blue white. Some lamps will have an aproximate colour temperature, others a colour rendering index, others will be cheap copies from the near or far east.

[Andrew C]

Might be worth asking in your physics dept. to see if they have any demo lamps you can see. We have Hg, Na and H₂ discharge lamps for studying spectral lines.

[dmxtothemax]

Most discharge lamps are just higher power versions of the floro tube.

And work buy using ultra violet light to excite the phospers on the inside of the lamp.

 

So quite similar to the flurescent tube we learnt about at AS. Ah, ok.

Exactly the same in fact.

 

From the end of the first paragraph here http://en.wikipedia.org/wiki/Gas-discharge_lamp

"The fluorescent lamp is perhaps the best known gas-discharge lamp."