Measurements of wavelength between 600 and 700 nm with a LED source is possible with all of our LED meters.  It is so close at the specified 660/665nm that there is basically no difference between values when read by the power meter. The reason being because the spectral width (bandwidth) of LED's are very wide. They call LED’s monochrome but unlike lasers that have a real monochrome output (narrow spectral width) LED’s are actually very width. When an LED's wavelength is specified it refers to the center peak of an actual LED like a 660nm/665nm has a spectrum that can be over 100nm in width.

The POF meters have a Silicon detector for lower wavelength. The Silicon detector detects light in a bandwidth from about 400nm to about 900nm.