When a stage lighting desk / Software controls channels for intensity, position, colour etc. it treats them in one of two ways – HTP and LTP. In the days before waggly mirrors and nodding buckets (that’s moving lights BTW) every stage lighting control channel was output on a Highest Takes Precedence (HTP) basis.
Intelligent lighting came along, with all it’s fancy effects and a-wagglin’ about all over the place and HTP channel control was just going to make a mess of all this new information that the lighting desk was spitting out. Latest Takes Precedence (LTP) was born to make it possible to cleanly control intelligent lighting using the traditional lighting control system – channel no. @ channel level ( 0-100%).
HTP (don’t forget – Highest Takes Precedence) means that if you have a light faded up on one fader and the same light in another fader too, the channel level that is highest (nearer 100%) is output to the stage. So, with HTP:
Channel 1 (fader 1) @ 75%
Channel 1 (fader 2) @ 50%
Then the light output on stage would be 75%.
And if you lowered fader 1 to zero the light would fade down to meet the 50% of fader 2 and then stay at 50%. HTP control channels are used for light intensity and simple lighting controls that are for controlling dimmers always use it.
HTP control channel – “Whoever shouts loudest, is right”.
LTP (Latest Takes Precedence) is a handy way of controlling intelligent lighting parameters that don’t related to intensity or colour mixing. It you need a colour wheel to change from blue to red, or a position to move from up to down, you want it to happen as you expect.
LTP control channels send the latest instruction to an intelligent fixture parameter and nothing changes until it sends another one on that channel. No mixing or adding, nothing.
LTP control channels are used in the majority of fixture parameters other than intensity and can be thought of as more of a switch, though it is sometimes possible to fade from one instruction to the next.
LTP control channel – “Whatever was just said – let’s do that !!”