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| 4x4 Quasar outside with light rain. Sketchy rigging done in a hurry, but it worked. |
It is awesome that you can dial in the color temperature you want, and dim the lights. The problem that comes up, which any set electrician will tell you, is flicker. Often a DP will have you dimming these tubes until they are barely on. Then they start flickering.
The problem is the load on the dimmer, usually a triac, is well below any threshold that is was designed for. One solution is a phantom load. I did this just last week on a 4x4 Crossfade fixture that was flickering. I added a 40 watt practical bulb--place in another room--and voila! the flicker was gone.
This is an awkward solution. On the 4x4s that I own, I added American DJ LED Dummy plugs which add a load to the circuit. These seemed to fix the problem most of the time using triac dimmers. The downside to these; they are expensive and they keep getting lost.
(I wonder if there is a problem with the American DJ plugs. The product has been discontinued.)
I have heard of variacs being used as Quasar dimmers. I tested this once. It didn't work well. The lights were erratic and still flickered. This makes sense. Generally, electronics do not like low or high voltage.
Which leads us to what this post is really all about.
I recently tried a Lutron CL Credenza Lamp dimmer on a Quasar Crossfade 4x4. Note I'm talking about the CL dimmers and not the standard Credenza dimmers. The Lutron CL dimmer line is specifically for dimming LEDs.
At the low threshold, the performance was amazing. It was possible to have the tubes barely glow with no flicker at any point. Very impressive.
The downside of these dimmers is their low rating for wattage. These dimmers are rated at 100 watts for LEDs and 250 watt resistive (tungsten). Perfect for 1 or 2 four-foot Quasar tubes, but under-rated for 4 tubes.
Testing a dimmer on a 4x4 Quasar, 200 watts total, the dimmer seemed to be getting excessively warm after about an hour. I would expect it to fail at some point with 4 tubes.
It is curious that these dimmers can handle 250 watts resistive, but only 100 watts LED.
I'm planning on keeping some of these dimmers around for dimming 1-2 Quasar tubes, but not using them on 4x4s.
They will be good to keep in my practical kit, too, and use them like they were intended as lamp dimmers.
Keeping with the random stream of dimmer thoughts in this post (bad pun?), I have been occasionally using my Lightronics AS42D DMX dimmer packs to control 4x4 Quasars hung overhead. Usually it is 1 head, 200 watts, per dimmer. Each dimmer is rated at 1200 watts.
I was concerned that flickering could be an issue, but the Lightronics performs well. I have not had any flickering issues when using 4x4s.
PS: Another cause of flickering with the Quasar Crossfade tubes is over-heating.
If
you use these, you know the tubes get surprisingly hot if they are on
for long periods of time like an hour plus. If they over-heat, they can
start erratically flickering.
Each
time I had trouble with flickering, over-heated tubes, they were: in a
Kino Flo 4x4 housing; at full output; had a soft-grid over the housing;
and were on for an hour or more. This is like the perfect storm to trap
the heat and over-heat the tubes.
I found a simple solution.
I
suspected that the reflector in the housing was making the situation
worse by trapping and reflecting heat back to the tubes. The reflector is almost function-less anyhow when used with Quasar tubes.
The
simple fix was to remove the reflectors from my Kino housing. Since
removing the reflectors, voila!, I had no issues with tubes over-heating and
flickering.
PPS: I know a popular modification is to add 6 Quasar tubes to a Kino Flo 4x4 housing. I love the idea. I have not done this becasue I believe the weight of 6 tubes is too much for the housing and especially the back-plate. If I do need more light, it is easy enough to add a second head, and gain a stop at the same time.
I once tried 4 of my Astera AX1 tubes in a 4x4 housing. It was not a good idea. Four Astera tubes are too heavy for the back plate. Two Asteras is the most I will put in housing.
Another option are home-made light boxes. This light-box, one of many, was made for me by the grips on a movie.
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| Coroplast lightbox for Astera or Quasar tubes |
It is simply a 1-inch board with Kino Flo clips with a coroplast skirt. (Coroplast, a brand name, is just corrugated plastic; an inexpensive, durable material.) To hang the box, a baby plate is screwed to the back. It is an easy, light-weight rig. Sometimes, I have taped diffusion inside the box to soften the light.
Update March 2022:
I can't remember the last time I used Kino Flo fluorescent tubes. It's amazing that these went from being ubiquitous on set to entirely replaced by other LED lights.
I've been using Lutron NTCL-250 dimmers for my crossfade tubes. They've worked well for me virtually eliminating dimmer/flicker issues.