The effectiveness of a light therapy session mainly depends on three parameters:

Time of exposure: to completely take advantage of the benefits of light therapy, it is recommended to carry out the session upon waking up, that is to say in the morning for someone who works all day. A light therapy session in the daytime will have a boosting effect comparable to that of coffee. A session in the evening is recommended for someone who works at night.
 

Light spectrum: it has been proven for a long time that photoreceptors are particularly sensitive to the blue part of the spectrum. A light therapy lamp whose spectrum has been enriched in blue will require a weaker spectrum for the same effectiveness.

Light intensity: light intensity, generally expressed in lux and measured at a given distance, is a very important parameter to consider when buying a light therapy device. The more powerful the light source, the shorter the session will be for the same effectiveness.
Example of a lamp placed at 30 cm: 500 lux = 2 hours; 10’000 lux = 0.5 hours