There are four distinct periods of incubation when embryos can die, and I provide common reasons for these losses in my incubation troubleshooting guide. Most candlers today use light-emitting diodes (LED’s) rather than electric bulbs. The advantage of LED is that it produces a bright white light without much heat. We expect to see either fertile eggs or clear eggs, as shown in our first candling after seven days, but occasionally the embryo starts to develop in a fertile egg and then dies. We call this “ early embryonic death” or sometimes just “early death”. After a week of incubation, place your egg onto your egg candler in a darkened room and turn on the light. You should be able to see shadows from inside the egg. With practice, you will identify fertile eggs by the dark dot, the embryo and the spider-like blood veins spreading out around the egg.

To be honest, a small ultra-bright torch is all you need, you can use your hand between the egg and torch to make a good seal.A thin ring around the inside of the egg indicates an early death. The embryo died at the start of incubation, usually within a couple of hours. These eggs are easy to identify and remove, and I have included a photo below.

I have tested several egg candlers, and in summary, I would not waste money on some of the cheap imported versions. The seal between the light source and the egg is not as good and doesn’t last. The LED is not usually very bright. After a week of incubation, you can be reasonably precise about the viability of the embryo. At 14 days, you can remove any eggs with embryos that have died and lessen the risk of a rotten egg exploding. Egg candlers can be mains powered or battery operated. They tend to come in two varieties: The first is like a torch with a rubber seal around the end, and the second is a table-top unit with a place to sit the egg.

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This ultra bright, LED Torch. I found normal LED torches with batteries go dim as the batteries age, this one is rechargeable and you can top it up from time to time to keep it super bright.