We recently received an email from a well-known lighting designer asking a pretty basic question about our Protective Filters. Here is their exact email:
“In Lightwright, we have always put down IRHS (infrared heat shield). Finally, after too many years of the shops and electricians asking “what’s that,” I see the sheets at the back of the Roscolux swatchbook. I use the IRHS to keep the R79 from burning out inside a Source 4-26°. So, what should I be specifiying R-1991 or R-1995 or R-3114?”
We figured that if this designer, who shall remain nameless, didn’t know which filter to use, many others wouldn’t either. Below, we clarify the difference between the Rosco Protective Filters and describe the best way to put them to work.
We have actually blogged about this product before when we talked about how “We Call It SUPER Heat Shield For A Reason.” R1991 is our most popular protective filter. Rosco Super Heat Shield is a proprietary material with a very high melting point that acts as a heat barrier to protect against convective heat – the mass of hot air that develops between the fixture’s lamp and the gel. This convective heat is the leading cause of premature gel failure, and creating a protective heat barrier with Super Heat Shield will make your gels last longer inside hot fixtures.
In the email we received, the designer calls out for an “IRHS (Infrared Heat Shield).” Based on that description, the filter they were looking for was probably R1995 Thermashield – an optical-grade, polyester film that features a proprietary, vacuum-deposited, reflective coating on one side. When placed in front of a lighting instrument, that coating will reflect back the infrared energy from the fixture, effectively reducing the radiant heat, while transmitting 80% of the visible light. The radiant heat present in non-visible light energy can accelerate the breakdown of color molecules inside a gel filter. By using Thermashield to reflect those wavelengths back, you can extend the life of your gels.
It is necessary to install the Thermashield with the coated side facing the lamp. Each sheet of Thermashield is clearly marked so that users can easily identify which side of the clear film should be facing the lamp. If the label becomes detached, or if the sheet is cut so that the label is no longer available, there is an alternative technique. When tested with an ohm meter, only the coated side (the side that must face the lamp) will be conductive.
No matter if you’re using R1991 Super Heat Shield or R1995 Thermashield – make sure that you keep at least a 1″ air-gap in-between the protective filter and the color filter. Otherwise, you’ll end up conducting the heat directly into the gel and render the protective filter useless. Use a gel extender if you can. Otherwise, you can insert the protective filter into the first gel frame slot of a Source 4 or S4 Par, with the color in the second gel frame slot – so long as the light doesn’t have too steep of a downward hanging angle.
Another great way to protect the gels in your Source 4s from infrared energy is to use our Hot Mirror dichroic glass filter. You can order an 86mm cut of the glass and install it using either a glass gobo holder or by inserting it into one of the gobo slots of the Universal Iris Slot Holder.
When it comes to protecting gels from the heat of a Source 4, R3114 isn’t going to be much help. It will, to some degree, serve as a heat barrier similar to the Super Heat Shied (just with a lower max. temperature). Ultraviolet energy most definitely will breakdown the color molecules inside a gel filter, but tungsten fixtures like the Source 4 hardly generate any UV energy in the first place – so there isn’t very much ultraviolet for this UV Filter to filter out.
R3114 is useful, however, on fixtures you may use that are high in UV energy, such as HMIs or fluorescent lights. In fact, the amount of UV concentrated on the bulb of T5 and T8 fluorescent tubes is so high that we make R3114 a standard component of our RoscoSleeves for those particular bulbs.
Hopefully, that helps explain the differences between our protective filters. If you have any further questions, contact Rosco Tech Support and they can help you find the answers you need.