Conventional Fixtures Using 750 S4 Lamps in a Small Theater

[SalvatoreDelorean]

Hi everybody,

I recently oversaw a pretty substantial gear purchase for my theater which included 20 brand new Source Fours. I meant to order 575s, but some way or another ended up with 750s. We've got our first show of the season coming up quickly, and I don't have time to get my hands on new lamps or exchange them with ETC before we're scheduled to hang. I ordered 575s because it's a relatively small black box and I don't have the need for higher-powered lamps, but I'm thinking about just going with it, at least for this show. Does anyone have any reasons why I shouldn't? My theater has an 18' grid and I usually don't have any throws longer than 30'. I figure too bright is better than too dim, and I can just set levels lower than I usually would, but is there anything I'm missing? Do they have different dimming curves or characteristics?

Thanks!

 

[jglodeklights]

Yes, generally it is better to have some ability to go brighter rather than the lights not being bright enough. However, at an 18' grid height you will run into some problems with 750's with less saturated gels such as L203 and R53 due to the amber shift that occurs as intensity drops. Especially L203. It gets heavy on the green. Very saturated colors such as R80 and L119 will be able to pop more, though. This is all assuming standard life lamps. 750 extended life lamps will be as bright as a standard life 575 lamp. So what did you actually get?

 

[lwinters630]

Is the actual bulb a 750. They may have 750 on the fixture, but check the bulbs.
"Just because it will go full, doesn't mean we have to or should!"
There is a theory (I can't remember the name) that uses no gels, they just use lots of fixtures and very the intensity to shift colors. For example 3 fixtures at 25% is a different color than 1 fixture at 75%.

 

[TDN]

I was going to chime in that if you ordered the long life 750 (which are marked 750x) you get about the same brightness as a 575. It's what I use in my spaces, since things go back and forth between our blackbox with a 15 foot grid and our mainstage, where my trim is normally at 22. I still find in the blackbox I don't run things up past about 70 percent unless it's a really saturated color. I say use the 750s, dim them down a bit and it'll be fine. Things may be a bit more amber, so you may have to shift your blues a touch more saturated (I'm looking at you, R60 at 65%)

 

[JD]

A fast fix, if they are 750's and they are too bright- Dim them to an acceptable level and add come color correction in a second gel frame until you get close to the "white" you want. Once you achieve this, use the new DMX level as your "full on." They will be inefficient as heck, but as long as the lamps don't drop below 80%, they should last a LONG time!

 

[Kelite]

This interesting tidbit has been useful over the years:

Act Voltage-Ave life-total output-Act Watts
85%......... 825% ....... 58%............ 78%
90% ........ 400% ....... 70%............ 85%
95% ........ 200% ........ 84%............ 93%
100% ...... 100% ........ 100%.......... 100%
105% ...... 54% ........... 119% ......... 108%
110% ....... 29% .......... 138%.......... 116%
115% ....... 16% ........... 160%.......... 124%


Additionally,
A 5% change in the voltage applied to the lamp results in:
-Halving or doubling the lamp life
-a 15% change in luminous flux
-an 8% change in power
-a 3% change in current
-a 2% change in color temperature (0.4% change per1% voltage.)

Osram Technology and Application Tungsten halogen Low Voltage Lamps Photo Optics, p.21
http://assets.sylvania.com/assets/documents/ENGR_BLTN9.9eec8e28-950e-4995-a67e-ceddfc343c65.pdf

 

[derekleffew]

This interesting tidbit has been useful over the years:

Act Voltage-Ave life-total output-Act Watts
85%......... 825% ....... 58%............ 78%
90% ........ 400% ....... 70%............ 85%
...

For those who prefer to roll their own,

lumens/LUMENS = (VOLTS/volts)^3.4
life/LIFE = (VOLTS/volts)^13 (I.e., reduce the volts to 90% and the life increases by 393%!)
EFFICIENCY/efficiency = (VOLTS/volts)^1.9
watts/WATTS = (volts/VOLTS)^1.6 (not 'squared' as you would get with a fixed resistance)
coltemp/COLTEMP = (volts/VOLTS)^0.42

Here is the above in a handy Excel spreadsheet: http://www.derekleffew.com/referencedocumentsandwebsites/LampFormulas2.xls?attredirects=0 .

Do we have anyone who can make that into an iPhone/android app?

 

[WooferHound]

Using a 2400 watt dimmer you can put
four 575 watt lights on it for a total of 2300 watts
or three 750 watt lights for a total of 2250 watts

 

[David Ashton]

For those who prefer to roll their own,

Here is the above in a handy Excel spreadsheet: http://www.derekleffew.com/referencedocumentsandwebsites/LampFormulas2.xls?attredirects=0 .

Do we have anyone who can make that into an iPhone/android app?

Caveat, these approximations apply from around 70% to around 110%, too high and the tungsten melts and too low and the halogen cycle stops and the filament becomes a heater but not much of a light emitter, so it's a useful approximation but don't bet your house on it.

 

[hobbsies]

Using a 2400 watt dimmer you can put
four 575 watt lights on it for a total of 2300 watts
or three 750 watt lights for a total of 2250 watts

Based on what I've learned on this forum, you're supposed to leave at least 20% of a dimmer's capacity unused, so for a 2.4k dimmer, you should only use max 2k or 16A. That's three 575's or two 750's. I believe it's due to heat build in cables up causing cable resistance to increase and thus wattage increase. Someone correct me if I'm wrong though.

 

[JD]

Based on what I've learned on this forum, you're supposed to leave at least 20% of a dimmer's capacity unused, so for a 2.4k dimmer, you should only use max 2k or 16A. That's three 575's or two 750's. I believe it's due to heat build in cables up causing cable resistance to increase and thus wattage increase. Someone correct me if I'm wrong though.

Actually, on any resistive load (such as a filament based lamp) any cable resistance will actually lower the load. The resistance of the cable is added to the resistance of the lamp. The line voltage being the same, the current will drop as the resistance goes up.
This often gets confused by the fact that an electronic ballast will increase it's current draw as available line voltage drops due to cable resistance.

As for dimmers, ETC dimmers are rated at 100%. Not so with all dimmers. Many have standard breakers which need the 20% derate.

I always believe in not loading out dimmers to 100%, however if the dimmer is rated at 100% then you can load it all the way. My preference is not to, but it is just that, my preference.

As for the cable capacity, see this thread- http://www.controlbooth.com/posts/202915/

 

[hobbsies]

Actually, on any resistive load (such as a filament based lamp) any cable resistance will actually lower the load. The resistance of the cable is added to the resistance of the lamp. The line voltage being the same, the current will drop as the resistance goes up.
This often gets confused by the fact that an electronic ballast will increase it's current draw as available line voltage drops due to cable resistance.

As for dimmers, ETC dimmers are rated at 100%. Not so with all dimmers. Many have standard breakers which need the 20% derate.

I always believe in not loading out dimmers to 100%, however if the dimmer is rated at 100% then you can load it all the way. My preference is not to, but it is just that, my preference.

As for the cable capacity, see this thread- http://www.controlbooth.com/posts/202915/

Thanks for clarifying

 

[DELO72]

Caveat, these approximations apply from around 70% to around 110%, too high and the tungsten melts and too low and the halogen cycle stops and the filament becomes a heater but not much of a light emitter, so it's a useful approximation but don't bet your house on it.

This is exactly correct.

FYI- the best advice I've seen on here was the one that said to use Color correction gel and profile the dimmer to a lower level. Otherwise your gels will completely put out the wrong color due to the amber shift, and "just use a more saturated color" is NOT a correct solution that will get you anything even CLOSE to the color you are looking for. More Amber wavelength does NOT equal more Total light.

Another side item to note on the "loading up a 2.4K dimmer discussion"- Loading up a dimmer to 100% capacity is bad for one addtional reason-- Lamps (like all products made in the world) are built to tolerances. a 575W lamp is almost NEVER exactly 575W. That is the target spec. it is designed to-- however ALL specs have a tolerance range that the finished product falls within and can still be sold as meeting spec. With Halogen lamps (ANSI) it is typically +/- 7% on wattage, +/- 10% on lumens, etc., for most lamp manufacturers.

WHICH MEANS-- your "575W lamp COULD be at the very high end of the spectrum and be a 612W lamp in reality. Try putting four 612W lamps on a 2400W dimmer and see what happens....

Cheers,

Mark

 

[David Ashton]

At risk of sounding pedantic I think JD meant neutral density gel rather than colour correction. I learned this the hard way trying to get a steel blue at a very low level, dimming down a Lee 117 to 30% gives a warm glow, but running near full and adding n.d. to reduce the intensity worked fine.

 

[Floobydust]

As a side note, there are 115 volt versions of the HPL lamps and 120 volt versions.
The 115's should be used on a dimmer circuit (as others detailed above), and the 120 volt versions should be used when plugging straight into power, bypassing any dimmers.

I found this out the hard way when new bulbs were failing within 10 hours of use. Switched to 120 volt versions with great success.

 

[DELO72]

At risk of sounding pedantic I think JD meant neutral density gel rather than colour correction. I learned this the hard way trying to get a steel blue at a very low level, dimming down a Lee 117 to 30% gives a warm glow, but running near full and adding n.d. to reduce the intensity worked fine.

You know... I didn't even think of ND! This is a perfect idea.

 

[jhochb]

For those who prefer to roll their own,

Here is the above in a handy Excel spreadsheet: http://www.derekleffew.com/referencedocumentsandwebsites/LampFormulas2.xls?attredirects=0 .

This is a great XL , thanks
Can a percent column be added for the math challenged among us?