the 803 I used reduces output 20.1%. On a KR1AA the filter can be placed between the glass and the optic. Do not try to clean the filter with alcohol, that removes the pigment and ruins the filter. The glass lens can be used as a template to cut around the filter.
On a Zebra or other lights that cant be opened, and dont have an optic under glass, the filter can be placed on top of the glass. Here is a video about that.
@Boaz sells Lee Zircon filters in large sheets, or you can buy the sample book if you only need a small amount
I dont recommend the Lee non Zircon Filter, it is less heat resistant.
here are the light transmissions for each filter..
Zircon 802: 75% transmission
Lee 248 Half minus green: 71.5%
Zircon 803: 79.9% transmission
Lee 249 -Quarter minus green : 81.5%
Zircon 804: 83.6% transmission
Zircon 805: 86.6% transmission
Lee 279 -Eighth minus green : 87.2%
the filter also lowers the CCT and slightly raises CRI Ra and R9. The filter wont turn a low cri LED into a High CRI LED.
It makes more sense to have an NTG50 4200K with no filter, than to have an SFT70 5000K or XHP50.3 Hi 5000K with filter..
A filter on a Low CRI LED such as the SFT, or on a green tinted 9050 LED such as the XHP, is better than nothing, but a poor substitute for a High CRI LED without green tint.
otoh, if SFT or XHP are the LEDs your light has.. a filter will knock down the green tint.. because the filter is a Pink tinted photo gel.
here is the result of Zircon 803 on the Low CRI SFT-70 5000K:
(duv data is from my Opple 3 at ceiling output (the actual values are not from a calibrated spectrometer, but show relative change)