showing dashed line in the legend box

edit

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');