Book 3 Chapter 10.3: the image (Image 11) is too noisy with `samples_per_pixel = 1000`

[phqb]

In the 3rd book, chapter 10.3, the book outputs this image which is too noisy for such a large samples_per_pixel

raytracing.github.io/books/RayTracingTheRestOfYourLife.html

Lines 3251 to 3257 in 0ab7db4

	<div class='together'>
	Updating `main.cc` to 1000 samples per pixel (not listed) yields:
	![<span class='num'>Image 11:</span> Cornell box, mixture density of cosine and light sampling
	](../images/img-3.11-cosine-and-light.jpg class='pixel')
	</div>

Here is my image with samples_per_pixel = 10 which is the same as the book's image

and with samples_per_pixel = 1000