difference between mole-richardson and Arri lights

[David Desio]

Yesterday I did a shoot and mixed and matched some lights, namely an Arri 2k tungsten fresnel and a mole richardson of the same type. I was using them both as the key, bouncing them into a 4x8 piece of white (I didn't have the power for anything bigger and had to really budget). Anyway I noticed that the Mole was very different in colortemp and intensity. The arri was bright and had a nice whitish almost neutral color while the mole was very tungsten-y and not as bright. I had to drop a double scrim in the arri to even it out. Anyone else ever noticed a difference or was there something wrong with the mole light?

[Travis Hale]

There is always a chance for color temp differences between lights, even among those of the same make and model. Assuming that the power source for each light is consistent, the problem you are describing might be due to the age of the elements/bulbs. The elements/bulbs can change their color output as they are used. Now, let's say you just picked up your lighting package from the rental company, among your heads one may have 1,000 hours of use, and another 200 hours, and so on. This will mean that each of your heads (even if they are all HMI or tungsten) could produce varying color temps.

 

It's good practice to let your lights warm up, then using a color meter you can determine the differences between each light, and gel them accordingly. If you have ever worked on a big production with lots of lights, you might notice a strip of tape on each head with markings like "1/4 CTO", "1/2 minus green", etc. These are usually the designations for which gels to put on the lights so they are all at at the same temperature.

 

Hope this helps.

 

Yesterday I did a shoot and mixed and matched some lights, namely an Arri 2k tungsten fresnel and a mole richardson of the same type. I was using them both as the key, bouncing them into a 4x8 piece of white (I didn't have the power for anything bigger and had to really budget). Anyway I noticed that the Mole was very different in colortemp and intensity. The arri was bright and had a nice whitish almost neutral color while the mole was very tungsten-y and not as bright. I had to drop a double scrim in the arri to even it out. Anyone else ever noticed a difference or was there something wrong with the mole light?

[David Desio]

I appreciate the input. When I asked the gaffer about this, he said that Arri's are supposedly 20% brighter than other lights, or so they claim.

[Charlie Balch]

Were both lights fairly new? I know the age of the bulb affects the color temperature...

[Chris Keth]

Did you check the cleanliness of the lens on the MR fixture? I've got them before that had enough dust in there to cut a full stop of light.

[Mathew Rudenberg]

Were both lights fairly new? I know the age of the bulb affects the color temperature...

 

 

Arri's do tend to be more efficient (especially their 1200 HMI pars) but a double is a full stop. For that much of a difference something major must be off. I don't thing the age of the tungsten globe alone could do it alone, they're usually fairly consistent. Several other things can affect the brightness and color temperature as well.

 

Did you check the basics?

 

If one light was spotted and one flooded that could easily make a full stop of difference (maybe the mole's mechanism was jammed)

 

Is it possible that one of the lights was on a dimmer?

 

Did you check the actual globes? Sometimes people put smaller globes in units for various reasons.

 

Dust can have a huge impact, if the reflector and the lens are dusty it can significantly reduce your output and warm the color temp, probably not a full stop though...

 

The size of the light matters - the big studio units have bigger lenses and reflectors and so put out more light, the smaller location lights (baby's) put out less. probably not a full stop though...

 

I have seen a severely damaged globe act inconsistently. After a hard knock that causes some of the filaments to cross or break the globe can burn much brighter or dimmer than usual (usually for a short time before failing)

[David Desio]

The arri unit is about 3 years old, the bulb was replaced about 6 months ago or so. I know because it's mine. The M/R is an older unit that lives on a grip truck and works mostly on location while the arri stays in the studio. The arri is not a studio light but a smaller location unit. Both were about half flood. I bet the M/R was knocked around a bit more than the arri and the lens looked like it had seen some better days now that I think about it. Interesting though that arri's are more efficient, I've always tended toward them anyway.

[robert duke]

Mole reflectors can burn esp in older units and units 2k and up. essentially dust gets on the reflector and when heated burns the reflector. Check the reflector next time, units that get exposed to weather, etc can rust as well.

 

all this can affect a lamps output.

 

also the reflector could have been out of focus. the position of the reflector in reference to the filament.

[David Desio]

great info from all you guys, if anything this prompts me to be more thorough when inspecting lights, other than the usual, do they turn on, are they close to thr right color temp, are any of the wires exposed...

[Brian Rose]

I recall David Mullen speaking about this very thing, either on this board, or in the book he co-authored with Malkiewicz. He mentions how tungstens tend to warm up (color tempwise) after a while, so if you've got a bulb that's clocked some hours on it, you may have to put a very mild blue gel to compensate.

 

BR

[John Sprung]

Another thing to look for on an older unit is electrical resistance. As surfaces tarnish, resistance goes up and voltage at the globe goes down. Connectors and switches start running hot when the lamp's been on for a while.

 

 

 

 

-- J.S.

[Hal Smith]

Another possibility is the Mole and the Arri had bulbs with nominally different rated voltages. In some bulb sizes it's possible to buy bulbs with different voltage ratings. A bulb rated at 130 volts will last a lot longer on 120 volts but it also will put out less light and will have a lower color temperature.

 

I'm most familar with the above principle in the HPL series bulbs my Source Four's use. I can get 120 volt HPL575WX's that actually have 130 or so volt filaments and will run 2,000 hours and put out 12,360 lumens at 3050K color temperature. I use them on theatre productions where it's nice to have bulbs that will last for a long run. But obviously I have to design for the reduced lumens per fixture.

 

But for movie and video work I use 120 volt HPL750's that are rated at 300 hours, put out 21900 lumens and have a 3250K CT. I have some true 120 volt HPL575's that last 300 hours, put out 16520 lumens, and have a 3250K CT.

 

Bottom line is I suspect your Mole might have some type of long life bulb in it. See if you can still read the ratings printed on the bulb. If it has an ANSI number it will be easy to research what you've got. http://www.bulbconnection.com is a good place to research bulbs.

[David Desio]

Thanks alot Hal, very insightful stuff. I've bookmarked the site for future reference.

[JD Hartman]

In this comparison it's a location Arri vs. a similar Mole fixture. Photo-metrics should be close if not the same if both fixtures have the same globe, but the Mole probably sees more duty on location. I'd wager that a dirty reflector and lens are reducing the output. It's a good practice to do some maintenance on all your fixtures about one a year. For Fresnel fixtures, removing the lens and running it through a dishwasher is a good idea. Even the globes can acquire a dirty film, an alcohol wipe down will remove that. Clean the reflectors as well. Check for bad sockets and wiring, missing/loose fasteners, before re-installing the globe.

[David Desio]

cool, thanks JD