it looks like 10hz is about as low as you can go and still have it be invisible (see below). There are several other studies that look at the effects in the Gamma band >30hz. I posted that particular study because it pointed out that the frequency needs to be phase matched to the individuals brain rhythm (maybe a reason why others can use the equipment that effects us without issue)
Critical flicker-fusion frequency as an indicator of human receptive field-like properties.
Campos EC, Bedell HE.
Abstract
A psychophysical function, believed to reflect receptive field-like properties, is described. It is based on the determination of the critical flicker fusion frequency (CFF) of a tiny test target, centered on a round background of fixed luminance, the size of which is varied as the test parameter. Under optimal conditions, the maximal obtained frequency difference is 10 Hz. This function is compared with the so-called sustained-like function, with which it has some common aspects. Additionally, a portion of the flicker-based function apparently derives from a non-sustained-like source.