halogen lamps in a moving head?

[uhhehhahh]

It seems like most moving heads and scanners etc, uses discharge lamps rather than halogen lamps, but are there other obvious reasons except for the fact that discharge lamps seems to have an higher output effect than halogen lamps? It seems like a much more expensive choice, as discharge lamps seems to have a much shorter life span?

 

I might have gotten this wrong, but it seems kinda normal for a discharge lamp to have an average life span of not over 3000 hours?

[ChazHS]

Halogen lamps have fillaments which quite easily break, especially when moving about. Discharge lamps have no fillament. Also, the colour temperatures are considerably different, halogens output a yellow-white where as discharge lamps generally output a blue-white, which looks whiter.

[csg]

there are several reasons for discharge lamps being used more commonly than tungsten lamps in moving lights

 

1) higher output for a given input power

2) the optical centre in discharge lamps is smaller for a given lumen output, which makes designing high performance optical systems easier

3) The higher efficiency of a discharge lamp over a halogen lamp makes thermal managment easier

4) the service life of a discharge lamp is usually longer than for a halogen lamp, particularly when mechanical stresses are taking into account

 

Whilst there are moving heads around which use tungsten sources, these are usually fixture either designed for tungsten balanced television or film applications, or those designed to blend in with conventional rigs ( eg vl5)

[uhhehhahh]

there are several reasons for discharge lamps being used more commonly than tungsten lamps in moving lights

 

1) higher output for a given input power

2) the optical centre in discharge lamps is smaller for a given lumen output, which makes designing high performance optical systems easier

3) The higher efficiency of a discharge lamp over a halogen lamp makes thermal managment easier

4) the service life of a discharge lamp is usually longer than for a halogen lamp, particularly when mechanical stresses are taking into account

 

Whilst there are moving heads around which use tungsten sources, these are usually fixture either designed for tungsten balanced television or film applications, or those designed to blend in with conventional rigs ( eg vl5)

 

 

interesting, so you actually say that halogen lamps usually have shorter life span than a discharge lamp?

[Brian]

interesting, so you actually say that halogen lamps usually have shorter life span than a discharge lamp?

Absolutely, something like the popular ELC, 250W with it's own reflector, is only rated at 50 hours. You can get 300 hour version but at the expense of lower output.

 

Moving up towards 1k lamps you're looking at around 750 hours for a normal output unit.

[uhhehhahh]

interesting, so you actually say that halogen lamps usually have shorter life span than a discharge lamp?

Absolutely, something like the popular ELC, 250W with it's own reflector, is only rated at 50 hours. You can get 300 hour version but at the expense of lower output.

 

Moving up towards 1k lamps you're looking at around 750 hours for a normal output unit.

 

 

What do you think would be a normal/average life span for a discharge lamp used in higher end equipment such as Martin/Robe/Clay Paky moving heads?

[mumbles]

We normally replace at 1000 hours, but they would run way beyond that, its just not nice when they do properly go.

 

Hours do rack up quicker with discharge fixtures though, as they strike at the beginning of the day and then often won't be turned off until the shows come down, whereas a tungsten lamp will only rack up the hours when in use.

[Jivemaster]

For fixed kit you may get 30% rated filament life in moving head applications. For touring, on the road, kit you may get 10% of rated filament life for lamps. Filaments for precision lamps are usually more fragile than GLS lamps.

 

With a discharge lamp there is no fillament so you get the full rated life wherever.

 

Lamp life on a filament is to the failure point -when the fillament breaks! The life of a discharge lamp is calculated to be the point when the light output has fallen to half the initial lumen output. HOWEVER although there may still be light left in the lamp the efficiency and striking characteristics will change and in the end catastrophic failure of the envelope may occur, making a huge bang and mess and shrapnel hazard. Lanterns for discharge lamps should be made to retain the shrapnel and absorb the energy.

[uhhehhahh]

We normally replace at 1000 hours, but they would run way beyond that, its just not nice when they do properly go.

 

Hours do rack up quicker with discharge fixtures though, as they strike at the beginning of the day and then often won't be turned off until the shows come down, whereas a tungsten lamp will only rack up the hours when in use.

 

 

Not sure I understand the difference, when you turn on the light in a discharge and then turn it off, isn´t that the same as when you turn on a halogen and then turn it off?

 

 

 

A concurrent post has been automatically merged from this point on.

 

For fixed kit you may get 30% rated filament life in moving head applications. For touring, on the road, kit you may get 10% of rated filament life for lamps. Filaments for precision lamps are usually more fragile than GLS lamps.

 

With a discharge lamp there is no fillament so you get the full rated life wherever.

 

Lamp life on a filament is to the failure point -when the fillament breaks! The life of a discharge lamp is calculated to be the point when the light output has fallen to half the initial lumen output. HOWEVER although there may still be light left in the lamp the efficiency and striking characteristics will change and in the end catastrophic failure of the envelope may occur, making a huge bang and mess and shrapnel hazard. Lanterns for discharge lamps should be made to retain the shrapnel and absorb the energy.

 

 

Thank you, interesting point about how the life is calculated differently depending on wether its a discharge and a halogen.

 

Do I understand it correct when you say that a halogen lamp used in a moving head will only get 30% of life compared to if it had been used in another context? And only 10% of its regular life span if it is on the road?

[Beachhouse13]

Not sure I understand the difference, when you turn on the light in a discharge and then turn it off, isn´t that the same as when you turn on a halogen and then turn it off?

 

In a discharge lamp you turn the light on before a show and use a shutter system to dim the lamp. So even if there is partial or no output coming from the fixture the lamp is still on. In a halogen you generally vary the intensity of the light by an electronic dimmer like you would any other halogen static fixture so that when there is no output the lamp is off and not eating up it's life time. Although there are some that have a mechanical diming system as well (i.e. Mac TW1)

[niclights]

As I understand, the discharge lamp will produce metal deposits during striking. These occur at decreasing rate until the gas has reached full temperature. I believe this is also why it is generally not recommended to run at reduced power for too long and why many manufacturers will recommend lamps are always allowed to reach full operating temperature for a few minutes before dousing/dimming.

 

This would result in loss of ouput, but I'm sure there is more to the subject. Perhaps the properties of the gas change too, making it increasingly harder to strike.

 

Obviously tungsten filament also suffers from degradation in use too but not in a way that would reduce output like this. Eventually the filament simply breaks.