Wavelengths are stored in the ctype field and determine the colour of the elements (e.g. PHOT, FILT, BRAY, BIZR, BIZS and BIZG.) They can be used as storage by setting the wavelengths to a certain amount and read that info by filtering out some wavelengths and letting others through. https://powdertoy.co.uk/Browse/View.html?ID=2332971 shows that use. Wavelengths are displayed at the HUD on top of the element name. In a full spectrum, the wavelengths on the left are red, and on the right they are blue. In between are the colours of the rainbow. When it isn't a full spectrum, then some colours will be missing. To set a wavelength, you need to set the ctype to get different wavelength. The wavelengths are: Wave NO . Ctype

--Blue wavelengths Rightmost) 1.1 2.2 3.4 4.8 5.16 6.32 7.64 8.128 9.256 10.512 11.1024 12.2048 13.4096 14.8192 15.16384 16.32768 17.65536 18.131072 19.262144 20.524288 21.1048576 22.2097152 23.4194304 24.8388608 25.16777216 26.33554432 27.67108864 28.134217728 29.268435456 30.536870912 Red Wavelengths Leftmost)

You can add them together, e.g. to get both wavelengths, 30 (the leftmost and the reddest wavelength) and 1 (the rightmost and the bluest wavelength) in the same spectra, you need to add the corresponding ctypes in the chart. 30.536870912 ctype for wave 30 = 536870912 1.1 ctype for wave 1 = 1 536870912 + 1 = 536870913, so set the ctype of the PHOT or FILT or whatever to 536870913 to get both wavelengths 30 and 1.