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Keep in mind, Tanning is merely the least bad form of sun exposure. Meaning, there is no 'safe tan'.
Generally yes, a lower SPF will allow a more controlled burn leading to a tan. However, you need to know your limits beforehand. Tan 5-10 min MAX per day to see how you react, the rest of the time, stick with the 50.
Also, you can burn in one exposure, but a tan may take 2-3 days to materialize.