Red Gel on HMI light?

J

jonliz

Member
Hope this isn't a stupid question. I've been googling for weeks and still can't seem to find the answer. Is it simply not possible to gel a HMI bulb to output strong red? I have a bunch of different colored gels, my green gel works really well and strong on my HMI but when I put my red gel on it seems to have almost no effect. By contrast, when I put this same gel on my 1k Tungsten Fresnel it comes out as a really really strong red.

I know one is going from 3200 to red, while the other would be starting at something closer to 5600 or 6000... I just can't seem to figure out a solution. Does that mean I have to double gel, go from 5600 to 3200, then put on the red filter?

This is really a question more for learning purposes, I know I can just rent a skypanel or DS1 etc, but I just wanna know. Does it have something to do with the science behind the HMI bulbs?

Thanks.
 
There is a mired calculator on the Lee Filters site which might help in dtermining the exact filtration to use. As for the spectral compsition of your source order a $7 spectroscope from Amazon and take a look.
 
Whether a tungsten light or an HMI, pretty much all the colors of the rainbow are present. But a tungsten lamp has a lot more on the red end of the spectrum while an HMI has a lot more on the blue end. A gel doesn't actually color light, it prevents other colors from passing through. So your red gel is stopping most of the blue and allowing most of the red to pass through. Note that it's not an absolute, and some stuff from throughout the spectrum makes it through anyway. But in general, on the tungsten there will be a lot of the red to get through whereas on the HMI there won't be very much in comparison. And that's why your red gelled HMI doesn't look very red. Doubling up on gels will simply block more light. It will narrow the range of colors that the gels allow to pass. This may mean a redder color but will also mean less brightness overall. In fact you could simply double the layers of your red gel.
 
If you're after really saturated colours, LEDs are your friend.

If you don't want good white light quality, they're cheap and easy.
 
You also don't mention the wattage of your fixtures or how the gels are mounted. Saturated colors can fade very quickly on a lamp, especially something like a fresnel at full spot
 
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