Hopefully they come out with a similar retrofit for the SL4 - you could use it on your delrin backup lights, and flooding aside, never have to worry about them running out during a dive. I wrote to UK about 12 months ago asking if such a product was in development, and they confirmed that they would be releasing LED products in the next 12 months - and it looks like they have! Good news for C4/C8 owners, as LED technology really seems to have taken off in the last year or so - they're no longer the little fuzzy balls of light that you used to get in hobby electronics kits.