MATLAB: Highlight Specific Portion of Graph

highlight curve

I am trying to highlight the visible wavelength that would appear on the curve (0.4-0.7) in figure 2. How do I do this? I.e. I want to highlight the portion of the curve that falls under the wavelength from 0.4-0.7.
clear all; clc
%Since we are working with a blackbody, we assume n=1, which
%then allows us to use Stefan-Boltzmann's constant and law
n=1;
T=1300; %[Kelvin]
sigma = 5.67e-8; %Stefan-Boltzmann constant [W/(m^2*K^4)]
C1=0.59585522e8; %[W*micrometers^4/m^2*Sr]
C2=14357.770; %[micrometer*K]
%Spectral Intensity
lambda=10e-2:0.1:10e2; %[micrometers]

I=(2*C1)./(n^2.*lambda.^5.*(exp(C2./(n.*lambda.*T))-1));
clf;figure(1)
semilogx(lambda,I)
%Emissive Power
wl=10e-2:0.05:10e2;%[micrometers]
E=(2*C1*pi)./(n^2.*wl.^5.*(exp(C2./(n.*wl.*T))-1));
figure(2)
semilogx(wl,E)
hold on

Best Answer

I am not ccertain what you want to highlight, since that region is vanishingly small.
Try this: 
%Emissive Power
wl=10e-2:0.05:10e2;%[micrometers]
E=(2*C1*pi)./(n^2.*wl.^5.*(exp(C2./(n.*wl.*T))-1));
Lv = (wl >= 0.4) & (wl <= 0.7);
figure(2)
plot(wl,E)
hold on
patch([wl(Lv) fliplr(wl(Lv))], [zeros(size(E(Lv))) fliplr(E(Lv))], 'r')
hold off
set(gca, 'XScale','log')
ylim([0 200])
figure(3)
plot(wl,E)
hold on
patch([wl(Lv) fliplr(wl(Lv))], [zeros(size(E(Lv))) ones(1,nnz(Lv))*max(ylim)], 'r', 'FaceAlpha',0.25)
hold off
set(gca, 'XScale','log')
ylim([0 200])
The first plot colourss the area under the curve, and the second plot highlights the entire region to the limits of the y-axis.
I restricted the y-axis limit in order to see the area of interest. With the normal limits, it iis simply not visible.
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