Heat shield is really effective. If you’ve not used it before though there is one golden rule. There has to be an air gap between the shield and the dark gels/filters you’re protecting, the bigger the better. It can be a few millimetres, say with gel held perfectly tight in frames in separate slots. That will work and you will see an improvement. But if you can increase that gap, ideally by getting the dark colours further from the light source, then you’ll get better results. It’s tricky to do this on profile/lieko type units. On fresnel/pc/flood/parcan type units a good method is to use is to put the heat shield in the normal gel-frame slot and to tape the dark gels to the barn-doors. You have to use much bigger cuts of the colours but they’ll last a lot longer. A lot of tv and film type lighting use this method all the time. Make sure you’ve got heat proof tape though, matt black ‘black-tak’ aluminium tape is perfect but expensive. You can also use cheap plumbers aluminiuminsulation tape, it’s silver so looks ugly but does the job just as well if looks aren’t a concern.
A final trick is to consider how the lights are focused. With fresnel/pc type units you adjust the spot/flood by physically moving the lamp closer to the lens. A fully flooded unit will have the lamp as close to the lens as possible meaning the heat is much much more direct as there’s less of an air gap between the heat source (the lamp) and the gel/filters. Refocusing slightly, moving the lamp back from the lens just a small amount, can have a big impact on gel/filter life time. You won’t be able to light such a wide area of course, but 4x not-quite-full-flood fresnels would be a better option than 3x full-flood fresnels covering the same sized area.
It’s a bit trickier with profile/zoom units as you’re moving the lens rather than the lamp, but the basic principle is try to focus with the lens further from the gel. Here the trick is more that a wider focus helps dissipate the heat over a larger area of the gel.
