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Monday, August 15, 2011

••◊ Getting ACTUAL 5500k Out of Promaster Fluorescents

Just an immediate heads up that this is a tech-worthy nerd blog entry for those inclined.  From my last blog entry you probably know that last weekend was my first foray into 48 hour film making.  Fun but challenging.  Also challenging was the budget.  We needed daylight balanced lights, but didn't have the budget to rent Kino's or a set of Arri HMI Frenels.  A couple sets of the Lowel Tota's magically (i.e. tragically) showed up, but I personally never want to deal with the issues they've created for me again.  However we did have our made-somewhere-in-Asia cheap Promaster 3-in-1 fluorescent lights.  Promaster also sells the bulbs rated at 5500k (daylight color temperature), which should have made life easy, kinda-sorta.

Like most cheap Asian products the advertising doesn't quite live up to the promise.  What, you say?  Low cost companies provide misleading specs?  Nah, never happens (sarcasm implied).  The bulbs are nowhere near an accurate 5500k color temperature or any daylight sort of balance.  As DP I knew I needed to move fast on this shoot and not be solving ridiculous color balance issues, so I came up with a reasonable solution - thus the subject of a new tech blog entry.

First, I think I need to show my test setup. I put a Gretag White Balance card in front of my camera lit by the Promaster bulbs with the camera white balance set to 5500k.  The test card should be a completely neutral color when the bulb color temperature matches the camera settings for white balance.  For those curious nerds ...no, the tungsten bulb in the background made no difference.  I turned it on and off to check.

Click on the picture below to see the RGB spectrum of the bulb.  Red is approximately the same as green, but there isn't enough blue.  If the green was mid-way between red and blue then it would just be a matter of adjusting the camera white balance color temperature to match - no luck there. 

The answer to this issue comes in the form of a Rosco #3208 quarter-blue gel.  I actually pre-tested this using the free color swatch book they give away at the dealers.  At first I was at another dealer who sells Lee brand gels and bought quarter-blue with the dealing telling me they were equivalent.  They aren't.  If you hold both up to the light you'll see that the Rosco is more purple-blue and the Lee is more cyan-blue.  So test before you buy.  All I can recommend at the moment is the Rosco gel because I don't know if Lee or GamColor make color spectrum equivalent gels.  They might, dunno.

This was my test setup.  I simply put the gel in front of the lens to ensure complete coverage.  As I mentioned before this was initially done with just the free swatch book sample.  Low cost!  The gels tend to hover around $7/sheet, so they aren't significantly expensive either.

The RGB "fixed" spectrum is shown below.  Notice how the red equals the green equals the blue?  Now that's good white balance!  The added benefit is that if I'm using this light as a key light I can just set the white balance to 5500k on the camera, gel the lights with the Rosco quarter blue, and not have to worry about white balance - i.e. I move like a grasshopper strapped to a bottle rocket from location to location.  Also the lights now better match daylight, making my life of dealing with mixed lighting problems a tiny bit easier.  No more yellow-green lighting to deal with.  Yeah! ...might also mean more time for the craft services table.  The downside? ...well, like with any gel you lose a bit of light.

The real news is that the solution does work and it's battle tested in the field as of last weekend.  It's also an order of magnitude cheaper than the Kino or Arri solution, for lower lighting power needs at least.  Enjoy!

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