copper bulb comparator output depends on oxidation level

A "Lit" copper bulb can be read as "15" redstone power with a comparator. This does not change with oxidation level. 

The proposition is that the output level read by the comparator depends on the oxidation level. 

1. Copper bulb: redstone level 14

2. Exposed copper bulb: redstone level  11

3. Weathered copper bulb: 8

4. Oxidized copper bulb: 5

(the proposed value would correspond to the light level the bulb produces, but the values that represent hard to obtain outputs could also be prefered, for example 7 or 9 cannot be obtained from a composter and could be better than 8).