The original 998 SI Combo had CCFL backlighting (which I assume yours is if your unit does not physically have "HD" in the model name and printed on the SD Card slot door) ...
The 998 HD SI Combo had LED backlighting (which was the only change made with the added "HD" designation ... It is easier for sunlight viewing)
The 999 HD SI Combo also has LED backlighting (which is easier for sunlight viewing) ...
Rickie