Candling means shining a light through an egg to watch the embryo develop without opening the shell. It is the simplest way to check fertility, follow growth and pull out dead eggs that could rot and contaminate the whole batch. Done well, it frees up space and improves your hatch rate.
When to candle your eggs
Do a first candling around day 7, when the blood vessels are already clearly visible. Check again around day 14 to confirm the embryo is growing. Avoid candling too often, since every trip out of the incubator cools the egg. For a chicken (21 days), candle on day 7 and day 14, then stop before lockdown on day 18 or 19.
The equipment you need
A simple strong LED candling lamp works, or a focused flashlight held against the large end of the egg. Work in a fully dark room, because contrast is what makes the inside readable. Wash your hands, handle the egg gently and quickly without shaking it, then put it straight back into the incubator.
What you see on day 7
A fertile egg shows a spider-web network of blood vessels radiating from a dark central spot, the embryo. A clear egg, where light passes through with nothing inside, is infertile. A blood ring, meaning a sharp red circle with no living network, signals early embryo death. Remove clear eggs and blood rings.
What you see on day 14
By now the embryo fills much of the egg and looks like a dark mass. You may even see movement and the growing air cell at the large end. An egg that was fertile on day 7 but now looks clear or cloudy with no vessels has stopped developing, so take it out.
Which eggs to remove
- Clear eggs on day 7 (infertile)
- Blood rings (early death)
- Cracked, weeping or foul-smelling eggs
- Eggs with no progress between day 7 and day 14
Common mistakes
Never toss an egg at the first doubt: dark or thick shelled eggs are hard to read, so wait for the next candling. Do not candle after lockdown so you do not disturb hatching. Always turn your eggs at least 2 times a day, ideally 3, until lockdown.