DIY Softbox with TL950 bi-pin T8 bulbs?

[dh003i]

I'm considering making 3 softboxes with 8 TL950 bulbs each. Each TL950 bulb produces 2000 lumens, so each softbox would produce 16,000 lumens (with all 3 making 48,000 lumens). 1000bulbs.com sells a case of 25x 48in TL950's for $100. They also sell ballasts, like this ballast (which with a 1.15 ballast factor would seem capable of driving a 2000 lumen bulb at 2300 lumens).

I've also found Medium bi-pin socket lampholders.

I'd like to have a way to make a portable "fixture" (the softbox) with the 8 TL950's in it, which plugs into an outlet. Does anyone know about wiring T8 bulbs & ballasts? What would I need to to do to make this? (I'd like to avoid buying 12 T8 fixture-ballasts, as that would be $247 + $115 shipping). Although maybe buying Metalux 4-Lamp fixture-ballasts from the local Lowes store would work. In any event, I still have no idea how to get them such that they can be powered by plugging into a wall outlet. Does anyone know how this could be done?

PS: I realize the TL950 or fluorescent bulbs aren't as good as other options, like Solux, for perfect lighting. But they seem like a good compromise for price, power-output, and also importantly heat-output (I don't want people I photograph to drip with sweat).

Also, Kino KF55 bulbs seem like they have a pretty good spectrum distribution, are they going to be substantially better than the TL950's in practice?

Here is a spectral chart of TL950 ("philips tl90") and some other fluorescent bulbs.

[vinny]

You must use t8 ballasts with t8 bulbs. There are other t8 daylight manufactures tha make globes for the movie industry. Kino flos vare t12 and cost much more. Your're looking at a huge, heavy soft box. Why not daylight cfls? Or the biax style tubes like kino barfly fixtures use?

[dh003i]

vinny,

Ahh thanks for telling me that the Kino's are T12's, I hadn't noticed that.

The reason I'm looking at the Philips TL950 T8's is because they have a very high CRI (98). The highest CRI CFL's I've found are 42W Bluemax's, which have a CRI of 93. The BlueMax's have 3.5 times the deviation from a blackbody as does the TL950.

Just looking up high CRI biax tubes, I haven't found any with a very high CRI. The highest CRI ones I've found so-far are these CoolLights ones, at CRI = 87. Its spectral energy distribution seems significantly more "peaky" than that of the TL950.

Are there any biax style tubes with a color-rendering performance as good as the TL950s?

[vinny]

Never heard of tl950's. Every motion picture production I've worked on in the last 10 years has used kino flo tubes and fixtures. If there were better options available, we'd be using them. If u make this giant softbox, how are u going to mount it and tilt up/down? You could mount them on a 4x4 sheet of thin plywood and add some diffusion directly over the tubes. Add some egg crate material over that for spill control and you'll have a large, soft source w/o the huge depth of a typical soft box.

[Jeff Bannow]

Would something like this help? They have a softbox that fits over it as well ...

C-1600 Cool Light

[dh003i]

Never heard of tl950's. Every motion picture production I've worked on in the last 10 years has used kino flo tubes and fixtures. If there were better options available, we'd be using them.

I'm sure they're great bulbs. Their spectral distribution looks similar to GE Sunshine or Philips Natural Sunshine T12's, which "]Steve Kim compared to TL950s. The TL950s also have a good spectral distribution and pass the tests they were put through. Steve Kim says he now uses TL950s in his studio and is happy with them.

It is a trade-off for me. The Kino Flo tubes have a slightly better spectral distribution, perhaps (only 2 major peaks instead of 3), but are significantly more expensive and aren't as efficient in terms of lumens/watt.

A case of 25 Philips TL950s for $102 including shipping (2,000 lumens at 5000K, or probably 1,818 lumens when filtered to 5500K x 24 = 43,632 lumens total). Two 6-packs of the Kino bulbs would cost $276 and produce 39,480 lumens. So I'd be spending more money to get slightly less total lumens from less efficient bulbs.

If u make this giant softbox, how are u going to mount it and tilt up/down? You could mount them on a 4x4 sheet of thin plywood and add some diffusion directly over the tubes. Add some egg crate material over that for spill control and you'll have a large, soft source w/o the huge depth of a typical soft box.

Yea, that's what I was thinking, to mount hem on plywood or something similar. Although maybe mount them on something a little smoother than plywood that won't give splinters.

Your idea about avoiding the huge depth of a typical soft-box is one of the things I was thinking of.

[dh003i]

Would something like this help? They have a softbox that fits over it as well ...

C-1600 Cool Light

I was considering a DIY solution like that too, but with higher CRI bulbs. BlueMax 42W CFLs are 93 CRI. The bulbs that they're selling from the website that has the C-1600 Cool Light are only 85 CRI (I called and asked). Apparently, the Fotodiox fixture can only take 2.35in diameter bulbs at most, which means the BlueMax 42W bulbs are out, along with a host of other other bulbs. In any event, 85 CRI is very low compared to the 98 CRI offered by the T8 bulbs, and is also low vs. 93 CRI of some CFLs.

[erie patsellis]

I'm looking at the 950s as well, if you look at how cool lights mounts theirs, using a yoke, it's not terribly hard to duplicate it on a different scale. If you know somebody that has a shear and brake, you can make an nice enclosure using .040 white aluminum. I'll dig some sources up for the odd bits and pieces off my other computer and post them this evening, the aquarium hobbyists have access to some really efficient reflectors and such that make life easy.

Another option would be a 150 CMH bulb, Cool lights has the bulb for ~$30 and you can buy an electronic ballast for around $100 from several aquarium suppliers as well.
If you want more lumens, the Phillips 575MR bulb is used in most of the HMI lights, the bulb is around $125, ballasts are in the $225 range, and they put out a heck of a lot of light (~ 49k if memory serves me)

I'm doing this conversion to a couple of Broncolor heads I have that are missing the flashtubes (they cost $600 each, so I"m not replacing them) and it will give me the ability to use either continuous light (for my scanback) or strobe with my modifiers interchangeably.

[dh003i]

erie,

The issue for me is figuring out how to get the T8 bulbs wired up to the electronic ballast...

Re the 150W CMH bulbs and Philips 575MR bulbs used in HMI lights (I've been unable to find the 575MR bulbs), these are less efficient, hotter running bulbs than the fluorescents, right? (also, the 150W CMH lists a CRI of 85, although I'm not sure that means it is worse than the Philips TL950, because it may have a smoother spectral distribution without spikes).

Looking at the spectral distribution chart for the best CFL's I've found that produces more than 20W (the BlueMax 42W, 93+ CRI), the I'm a little bit skeptical that they can compete with the TL950 fluorescent tubes:

Attachment 44684

There are 3 fat hums and 3 major spikes in the blue-green range. I would like to comment BlueMax for actually providing a meaningful continuous spectral distribution chart. FarmTek / ValuTek just provides a bar graph for their 125W 93 CRI bulb, which does not show intensity spikes at narrow wavelength bands.

PS: See my comments on a DIY softbox here and also my comments on the DIY Spyderlight (I didn't write the article, my comments are posted under dh003i). At 95% reflective, Behr Premium Plus Ultra Pure White #7050 paint is an excellent reflective material. I've determined that about 43,000 lumens is what I'd like to work with.

These formulas are useful for determining how many lumens you need:

GN = Distance × f/stop

GN = √(0.005 × Lumens × shutter time × Reflector Factor × ISO)

I assume a Reflector Factor of 1.176 for a softbox, calculated from this statement: "just under 10,000 lumens and gets you about 1/60th, f/2.8 on ISO 200 at 5 feet away." Ergo, the Reflector Factor = GN² / (0.005 × Lumens × shutter time × ISO) = (5 × 2.8)² / (0.005 × 10,000 × 1/60 × 200) = 1.176.

Assuming we wanted to shoot at ISO 400 for a 1/60s exposure at f/8, with the soft-box positioned 5 ft away from the subject, here's how many Lumens we'd need:

Lumens = GN² / (0.005 x shutter time x Reflector Factor x ISO)
Lumens = (5 × 8)² / (0.005 × 1/60 × 1.176 × 400)
Lumens = 40,816

Hence, how I figure that I'd need 24 of the TL950 2000 lumen 5000K T8 bulbs, split into 3 soft-boxes with 8 tubes each.

[vinny]

You should be using shiny aluminum for reflector material, especially since you seem to be obsessed with cri graphs and maximum output.