Why did 405 look so good?

[ppppenguin]

In the professional/broadcast TV world one of the standard test waveforms has switched APL (average picture level). So a ramp or staircase on about 1 in 5 lines, the remaining lines switching from black to white every half second or so. This shows up any black level clamping weaknesses quite dramatically. I've never converted it to 405 and fed it to any TVs. Not sure I'd want to see the results