showing dashed line in the legend box

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Could anyone let me know how you can change the style of the line in the legend box? I'm struggling with this for 2 hours. I can only change the fontsize of legend_label and color and etc. Please help me!

This is a part of my code for the plot

Lg1=plot(f1, (x, 1, 100),  ticks=[None, [0.000005, 1/5, 10^-5, 10^-4, 10^-3, 10^-2, 10^-1]], scale=('loglog', 10), ymin=0, ymax=1, axes_labels=['Distance between led and camera [m]','Illuminace on camera sensor[lux]'],axes=None, axes_pad=False, legend_label='$I=2cd$, $L_s=50m$', frame=True, color='blue');