ADS-L and ADS-B are like javascript and java.

The name is the same, but they are not compatible in any way or function.

The advantage of ADS-L currently would be very low because the spec was 'just' released (last year) so i doubt it would be in use a lot. But would love to stand corrected on that one!.

The ADS-L Technical Specifications are a subset of the ADS-B Technical Specifications which are laid down in the ICAO Annex 10. The added value of the ADS-L protocol is to accomodate ADS-B but also non-certified devices including Flarm, Neurones, PilotAware, etc. So, the answer is: the ADS-B devices are interoperable and efficient in an ADS-L environment.

My understanding is that ADS.L requires a link from the device to a GPS. This means that a standard transponder with S mode does not comply unless it is equipped with Extended Squitter and GPS connected ( certified?). This requirement could make making current equipment suitable costly…..

Thanks for your answers!
[~121] : I think you are wrong. According to the below linked (maybe outdated) document, it seems that a GA plane equipped with ADS-B is NOT able to see ADS-L traffic and vice versa, because at least of different used frequencies.

Here a re-broadcast of ADS-L traffic via UAT might be the solution to make it visible also in GA cockpits.

Is EASA aware of this? [~33687] : Can you make a statement on this please? How can it be assured, that ADS-B equipped GA-Planes are able to see ADS-L traffic (and vice-versa)?

Here the above mentioned link:
https://www.easa.europa.eu/sites/default/files/dfu/4._iconspicuity_ads-…

Hi Andreas, No ADS-B In on a GA aircraft cannot see ADS-L.
ADS-L is a subset of ADS-B data including position and GNSS altitude transmitted on 860 MHz. You need an extra receiver in your aircraft in order to see ADS-L equiped aircraft.
Therefore we have proposed, for a long time, to stay with the international standard for Electronic Conspicuity just like the UK is doing now. Certified ADS-B transponder or low power ADS-B on 1090 MHZ for manned aviation and ADS-B on 978 MHz (ADS-B UAT frequency) for unmanned BVLOS operations.
Some people already suggested to use the new EASA ADS-L standard only for Remote ID instead of the WIFI/Bluetooth protocol, and follow the UK and the coming ICAO standard “REDUCED CAPABILITY 1090 MHZ ADS-B EQUIPMENT” (i.e. low power ADS-B) for electronic conspicuity on GA aircrafts.