A practical approach is usually better than trying to “win” the argument with research. Reassure parents calmly, then visibly make the light gentler: bounce the flash, use a softbox or diffuser, lower the flash power, and keep some ambient light in the room if possible. That makes the setup look and feel less harsh, which often matters more to worried parents than a technical explanation.

A good message is: “I’ll use soft, indirect light so it’s more comfortable.” That is simple, accurate, and client-friendly. Avoid sounding dismissive or telling them they are wrong. If they remain uneasy, don’t push—adapt the setup if you can.

Also remember that parents may react not only to safety concerns, but to whether the baby seems startled or upset. If the child becomes distressed after flashes, parents will likely associate that with your lighting regardless of the science. Using softer, less direct light and lenses/settings that need less added light can help.

In short: reassure briefly, demonstrate care with a softer lighting setup, and prioritize the parents’ comfort as part of the service.