How to shade area under curve between x values

I can't get the area to fill between the dimensions quite right, it keeps shaping wrong area, so far i have this code below

close
clear
clc
r_d = 1.50e11; % distance from Earth to Sun
r_s = (1.39e9)/2; % radius of the sun 
fw =(r_s/r_d)^2;
t_s = 5800; % temp in kelvin
h = 6.626e-34; % in J*s
k_b = 1.381e-23; % in J/K
c = 2.998e8; % in m/s
syms lambda L_sun
lambda = (0.001:0.01:3)*1e-6;
L_sun = fw .* (2*pi*h*c.^2) ./ lambda.^5 .*...
    1./(exp((h*c)./(lambda*k_b*t_s)) -1);
figure(1)
plot(lambda, L_sun, 'b-', 'LineWidth', 2);
xlim([0 3e-6]);
xlabel('Wavelength (um)');
ylabel('Spectral Irradiance (W*m^2/m^-1)');
legend('L_s_u_n')
set(gcf, 'PaperPositionMode', 'manual');
set(gcf, 'PaperUnits', 'inches');
set(gcf, 'PaperPosition', [0 0 6.75 5]);
print('SolarIrradiance.tif', '-dpng', '-r600')
saveas(gcf, 'SolarIrradiance.fig')
%%
% Part 2.
maxL_sun = max(L_sun);
lambda_max = lambda(51);
% i. this falls in the visible region
% ii. uv = 6.4%, vis = 48%, and ir = 45.6%
% the energy for uv = 87, vis = 565, and ir = 623
UV = L_sun(1:38);
Vis = L_sun(39:78);
IR = L_sun(79:300);
UV_Vis_IR_fig = openfig('SolarIrradiance.fig');
hold on

and i need to shade the UV, Vis, and IR regions of a previously made graph and save it as a new one

Answer 1

[Image Analyst]

Try using area() to plot instead of plot().