Distance, decay and cut-off of a point light
The camera looks straight down. The picture is the pool of light of the light at 2 m. The 3 m cut-off column is the fourth in the table.
three.js has six kinds of light, each with its own unit and cost. You learn what they are for, how a point light fades with distance (the decay), and why twenty point lights is a mistake: each light adds work to every pixel.
Change the code and press Run (Ctrl+Enter). Predict what will happen first, then break it on purpose and read what changes. Your edits are saved and match the lesson page.
Ready for more? This phase has 5 hands-on exercises with automatic checks.
Practice questions
Write the code in the editor, run it, then open the model answer to compare.
Choose lights for the showroom: one that makes a shadow, one that keeps shadows from going black. Write the two lines.
The pool of light must stop 3 m from a lamp, with the default fading. Which property do you set?
Explain it without notes
A point light of 10 cd hangs 4 m above a floor. By what factor does the light on the floor change if it moves to 2 m, and what does decay 0 change?
Why do 20 point lights cost more than one, even if only one mesh is in the scene?
Console
Nothing logged yet.Expected console output
point light, intensity 10 (candela): floor pixel straight below
height decay 2 (default) decay 1 decay 0 decay 2, distance 3
1 m 255 255 255 255
2 m 228 255 255 187
3 m 158 255 255 0
4 m 122 228 255 0
power of a 10 cd point light: 125.7 lm