And that temperature value is about 72 degrees Celsius. That's the melting temperature of the DNA molecule, as shown in the following diagram. So this temperature value describes this point on a curve. And that's essentially the point where exactly half of those DNA molecules or exactly half of a DNA molecule, has associated its double helix structure. Now, as I mentioned earlier, in the double helix, the bases are interacting via non Covalent bonds. And this interferes with the ability of those bases to actually absorb the light.