The Powerful Effect Of Light On Your Cycle


Women’s cycles are very much connected with the cycle of the moon. Both are roughly 29 days (although a healthy menstrual cycle can range from 25 to 35 days in length). Additionally, with bodies that are made up of a majority of water, the moon exerts a pull on us similarly to the way it effects the tides. Before the advent of electricity and increased night-time night exposure, the majority of women ovulated at the time of the full moon and menstruated at the time of the new moon, when the sky is dark. A proportion of women did the opposite, menstruating on the full moon and ovulating on the new moon.

Women who are not on hormonal contraceptives that dictate their cycle and who limit exposure to light after dark often come into alignment with this lunar rhythm again.

In fact, simply managing the amount of light you are exposed to after dark and while you sleep can be a powerful tool for regulating your cycle and eliminating all sorts of so-called period problems.

Issues Caused By Too Much Light Exposure

According to Joy DeFelice, one of the leading researchers on light exposure and changes in the menstrual cycle, even minimal light exposure at night, particularly while sleeping, can cause cycle irregularities, and irregular cervical fluid patterns in particular.

In one clinical study, she found that the following issues were often triggered, at least in part, by light exposure:

  • No dry cervical fluid days after the period and shortening cycles
  • Fertile cervical fluid takes a long time to reach its peak
  • Cervical fluid presence is patchy and stops and starts again leading up to the peak day
  • Mid cycle spotting
  • Short luteal phase (time between ovulation and the start of the period)
  • Anovulatory cycles (in which ovulation does not occur)
  • Very irregular cycles

Why It’s Important

Irregular cycles and infrequent ovulation are both also the result of and contribute to hormonal imbalances that can compromise fertility, deplete energy, increase the severity of mood swings and the experience of PMS.

In addition, Joy DeFelice has found that women with a history of miscarriages have a greater success rate of bringing a pregnancy to term when limiting exposure to light at night.

How It Works

The menstrual cycle begins in the brain when the hypothalamus tells another part of the brain, the pituitary gland, to produce follicle-stimulating hormone (FSH). FSH acts as the messenger that tells the ovary that it’s time to start maturing an egg, and in turn, the maturing egg follicle begins to produce an increasing amount of estrogen. This estrogen results in fertile-quality cervical fluid and eventually ovulation, when it reaches the right amount.

When the body is exposed to light at night, even while sleeping, the pineal gland (also in the brain) registers the light exposure. One of the pineal gland’s main responsibilities is producing melatonin, which helps to regulate your circadian rhythm. Melatonin is meant to be high at night and low in the morning. When the pineal gland is exposed to light, it makes much less melatonin. Melatonin has an effect on the hypothalamus, so imbalanced melatonin as a result of night-time light exposure can cause a hormone cascade issue that prevents proper communication between the brain and the ovaries.

Ok, we’re done with the hard science part of this (whew!)…

Limiting Light Exposure To Regulate The Cycle

Now that we’ve gone through all that, the good news is that the fix is relatively simple. According to Joy DeFelice, limiting your light exposure for just 2 to 3 cycles will clear up any cycle irregularities that are caused by it.

If light comes in through your windows at night, invest in good blinds or curtains that keep the majority of it out. (The only exception to this is natural moonlight). You may also choose to sleep with an eye mask. Just remember, that the pineal gland can register light through your nostrils and ears as well, so a mask alone is not enough. You should also unplug appliances, or remove them from the bedroom, if they emit light.

If you tend to wake up in the middle of the night to use the bathroom, consider using a red nightlight in the hall or bathroom so you do not have to expose yourself to a light source to navigate around your home.

The trick is to limit as much light as you can—but you don’t have to blacken your windows so much that no light comes in in the morning.


Take It Further

full-moon-lunar-cycleI often recommend that my clients with irregular cycles address the amount of light they are exposed to at night, and use the moon cycle as a guide in the absence of an irregular cycle. Women are very much connected to the lunar cycle, and observing the moon’s various stages can help to regulate the cycle.

I recommend sleeping in complete darkness except for the three days around the full moon (the night before, the night of, and the night after). If you have exposure to natural moonlight, just leave the curtains open. Otherwise you may choose to sleep without your eyemask, crack the curtains or sleep with a nightlight on in the hallway and the door cracked.

This practice is adopted from Louise Lacy’s “Lunaception,” which inspired much of Joy DeFelice’s work. Notably, Joy has found limited benefits to admitting light into the room around the full moon. I still find that this practice helps women with irregular or absent periods to internalize the moon’s cycle in order to regulate their own.

Follow up listening: The Fertility Friday Podcast – Interview with Joy DeFelice

Kara DeDonato helps women get their fertility goddess on. Because fertility is so much more than the ability to bear children. Fertility is healthy, pleasure-seeking, vibrant, productive, creative, sexy, happy and fierce. Afterall, Aphrodite was a fertility goddess. Kara works with women to troubleshoot their monthly cycles and digestion so that they can feel their best and be their best selves. Through her #ditchthepill initiatives, she helps women transition from the pill to fertile as seamlessly as possible. You can find her on Twitter and Instagram @karadedo and

1 Trackbacks & Pingbacks

  1. The Powerful Effect of Light on Your Cycle | Libera Wellness

Leave a comment

Your email address will not be published.