PHOT frequency.

@Creepychair (View Post)

 It is the 'wavelength' of the PHOT, which is determined by its .ctype.

The .ctype can change when (btw these things also apply for BRAY):

• They pass thru FILT 
• They collide with certain coloring elements (e.g. URAN)

Yeh. More info about this can be found on the wiki. It is the ability of FILT to change BRAY .ctypes that is behind modern TPT FILT electronics. Cool stuff. Oh, and if you're wondering what the heckles a ctype is:

All particles in the simulation have these thingies called fields. These are just numbers that determine certain stuff that a particle does. Here are the particle fields:

• type: Each element type, say DUST, has an element ID. For DUST, this is 1.
• Particle ID: Not to be confused with element IDs. This determines the order in which particles are updated.
• tmp, tmp2, life, ctype: These do different things for different elements when set to certain values. For example, VIBR with a tmp of over 9000 will explode. To learn what each of these fields does for each particle, look it up on the Wiki, or, if you understand C++ code, look through source code...
• dcolor: Have you seen the deco menu before? It can be accessed by pressing 'B'. This allows you to 'color' elements, and these colors can be turned off or on by pressing Ctrl+B. As you may know, colors are usually represented as hex values (e.g. #FF4C74458) because computers only understand numbers and all other boring stuff that we make it deal with. So dcolor is also a number.
• vx, vy: Velocity fields. Say a particle has vx=4, vy=7. The particle will move 4 pixels to the right and 7 pixels downwards (in TPT, x goes positive to the right, and y goes down.)
• flags: I'm not even sure what these are for. I might search through source code (fun) to find out.

EDIT: erm. uhm. It seems he does know what deco and ctypes are... meh, hopefully the particle fields part helped ;-;