The x*y notation means “x to the power of y”. So, x2 is x squared, x*3 is x cubed, and so on. The “3x the previous mode” shape is a logarithm base 3 with the number of modes chosen to hit a specific ratio.

For example, nine evenly-spaced levels from 0.1 lm to 1000 lm, using a few different curve shapes…

x**2

x**3

x**5

x**9

log 3

0.1

0.1

0.1

0.1

0.1

18

4.5

1.3

0.6

0.3

66

23

6.9

2.8

1.0

145

66

24

10

3.1

255

143

65

31

10

395

265

150

84

31

566

442

307

208

100

768

684

574

472

316

1000

1000

1000

1000

1000

For a light like this, I would probably go with fewer modes and a curve from one of the middle columns. For example, six modes with a x**5 shape it would be: 0.1, 3.8, 30, 128, 398, 1000.