Paul C. Buff, Inc. Technical Forum

Hi there, Tech support:

It looks like two of my WL10,000 strobes need new flash tubes. :(

I guess I shouldn't be surprised considering that the silver paint that lines the inner circle of the tubes is almost completely gone (I think I have had the same tubes since I bought them new in 1995).

So what are the reasons for the UV coated and the non-UV coated tubes for the old WL10K series lights? Are the UV coated ones at a different color temperture?

and will it make a difference if I am using the strobes in a white umbrella or softlighter type modifier?

also, since I tend to mix my strobes with my speedlights, will that make a difference in which tubes to use?

Thanks in advance.

Very good question. Regular, non UV coated tubes emit light at all visible wavelengths as well as some in the non-visible regions like Ultra Violet and Infrared. Under many circumstances, this will not be a problem, and they would be OK to use.

However, where you will run into problems is when you introduce certain things into the mix, especially white fabrics. Most white fabrics, papers, and some paints these days have been treated with optical brighteners, which will fluoresce, or glow, under UV light. The best way to describe this is white clothing under a black light. This will have a bright blue/purple glow that other items do not have. These optical brighteners are used to "make your whites whiter".

The practical drawback for photographers is if you have non-UV coated tubes, and shoot through softboxes, umbrellas, scrims, etc. that use these brighteners, you will end up with a very weird blue cast across the image, that may not balance well to another light that is using, say, a silver umbrella. This discrepancy can be upwards of 1000K difference.

Also, even if your modifiers are OK, and you are shooting a person with a white shirt, or white wedding dress, that can get a blue tint, or even create a blue glow, that will not match the rest of the scene in color temperature, even those areas lit by the same light.

We work to ensure the fabrics we use are UV light safe, though many inexpensive alternatives on the market (and some "premium branded" items) do not take such care. We cannot control the fabrics used as the subject, however.

The non-coated tubes for the 10K/5K are 5600K, as dictated by the tube gasses and other spcifications. The coated tubes are the same as the non coated, except coated with a substance, which has a yellowish tinge. This tinge will bring the color temperature down to about 5200K.

Speedlites are 5600K to 6000K, depending on the model, and likely the power used, though they can yellow with age. Also, any fabric modifier will alter the color temperature some (usually down).

For most work, it should not be a big problem to mix UV coated tubes and speedlites. However, speedlites are quite easily gel-able to bring them to any color temperature desired.

Thank You, Tech Support.

OK, one more question:

How can I be sure whether the one remaining tube I have currently is UV coated or non UV coated?

I would prefer to match the other tube I have right now.

Thanks in advance.

It will be somewhat hard to tell without a comparison or experience. But, if you place the tube on a white piece of paper, you should be able to tell if there is a yellow cast. I find this easier to judge if I am in daylight.

Most 5K and 10K lights did not ship with UV tubes, but if they did, they would have "UV" in the serial number. This would not account for any replacement tubes that would have been installed.

Thanks.

The building across the street from us is white, so what I did was hold the tube up in front of my eye and looked through the glass of the tube at the white building and it seems that there is no difference in color, so I am guessing I will order that NON UV coated tubes.

Thanks for all your help.