http://shop.leefiltersusa.com/Swatch-Book-Designers-Edition-SWB.htm
For heat concerns, Lee makes a Zircon line that is heat resistant:
The 802 Zircon Minus Green reduces lumens by 25, that would be closest to the 1/2 minus Green, that reduces by 28
the following percent numbers are the amount of light transmitted, so 71.5% transmission means 28.5% lumen reduction…
Lee 248 Half minus green: 71.5%
Zircon 802: 75%
Zircon 803: 79.9%
Lee 249 -Quarter minus green : 81.5%
Zircon 804: 83.6%
Zircon 805: 86.6%
Lee 279 -Eighth minus green : 87.2%
Discussed here
Examples of with and without Lee