Ultimate light filtering calculator

Version 3 of the calculator is out!

Introduction

The point of this blog post is to provide an accurate examination of light filtering glasses, how light affects melatonin and the boundaries that should be considered when striving to ensure a good circadian health. A calculator is also given out that you can use to calculate the impact of your current dark period setup on your melatonin levels, which will be gone over excessively in this blog post. The purpose of this calculator is to be as newbie-friendly as possible, and the outputs will therefore be as simple as possible.

How to use the program

When you open the spreadsheet, the first thing you need to do is to copy the file and save it on your own drive, as described in cell B1.

Next, there are multiple different settings for you to play around with. It is recommended that you go for the most extreme settings in your environment, which means that distances should be assumed to be minimal etc.

In the current version of the calculator, there’s an option to add up to 5 different light sources, for example if you’re sitting in a room with a light and a computer screen, those would need 2 separate rows to accurately determine the effect that light from those 2 sources have on you.

Inputs

Temperature (B3:B8): Here, you should input the color temperature of the environment you are in. If you are using a screen filtering software on your computer, input that value. Purchased light bulbs also have their temperatures stated on their package.

Distance (C3:C8): Type the distance to the light source.

Power (D3:D8): Type the power output of the light source. If you don’t know what it is, you can find several approximations online.

Light type (E3:E8): Select which type of light you want to see the effects of. Different types of light convert the power to different illuminating rates.

Light distribution (F3:F8): Change in which directions the light being emitted is concentrated. For light bulbs, you can enter 360, for computer screens you can use 120 and so on.

Exposure duration (G3): The longer you expose yourself to light, the more your melatonin is going to be impacted. Here it is recommended for you to use the full duration of your awake dark period, but if you want to see how much removing your glasses for only a short duration will affect your melatonin levels, you can alter this number.

Melatonin suppression boundary (G3): Input at what melatonin suppression percent you want to receive a warning. The exact recommended percentage is not known yet, but based on this study1, a reduction of SWS was noted at this level.

Best filter match (H3): Look at column K and see which color best matches the filtering glasses that you are using, and type the corresponding number on column J into H4. If you are not using glasses, leave H4 empty or as “0”. If you know the filtering specifications of your glasses and they are not available in the list, you can enter the “Behind the scenes” tab and manually input the specifications there.

Outputs

After all information has been inserted, you will see what the expected melatonin suppression percent will be in cell B8. If this number is higher than your melatonin suppression boundary, a warning message will be visible on cell B11. You will also see the expected melatonin phase shift in cell C8, where a smaller number is better.

Unless you want to manually alter something behind the scenes, there is really no reason to access that tab. If you don’t want to bother with it or see the math used, stay on the “Inputs” tab.

Filtering glasses

First, why do different filtering glasses produce different results? Well, different wavelengths of light will affect the melatonin production at different rates. Additionally, different filtering glasses will filter out certain ranges of light more than others. Determining the exact filtering properties of glasses can be very tricky without fancy equipment; to make things simple a picture with different colors is also with the purpose of allowing you to make a visual comparison between your laser filtering glasses and the references, which is applicable to no-brand glasses. The accuracy of this comparison will not be all too high, especially since glasses which appear very similar in color might actually filter out certain ranges of light differently than others. Still, it is the easiest solution available for you, but you should still take the results with a grain of salt..

As one study points out, different wavelengths of light suppress melatonin at different intensities2. Based on this information, the sum of the melatonin suppression from all light emitted from different temperatures can be calculated and used to approximate the total suppression. Note that in this study the baseline for a 2 hour exposure, even in total darkness, results in a reduction of melatonin levels by 7%. This is because of a natural reduction of melatonin, and is not what we are interested in. The purpose of this calculator is only to provide the effects of artificial melatonin reduction, and because of that, the light wavelength suppression reference will be stated as 0% at 0 lux, regardless of the exposure time.

 

The quantum sensitivity of light is also considered, which is the relative effect that different wavelengths of light has on melatonin levels. For example, light at 464 nm has the highest quantum sensitivity at 1.00, compared to 550 nm with a quantum sensitivity of around 0.048. What this means is that exposure to light at 464 nm is going to be more detrimental than light exposure at 550 nm.

Calculations

Because no equation for the relative quantum sensitivity was given in the research paper, it was recreated using pixel counting and Excel’s trendline feature:

The total suppression was calculable by breaking the total lux emitted by a light source into all individual wavelengths and multiplying that with the suppression each wavelength produces. The values are then added together to show how much suppression occurs at certain durations of exposure at certain distances.

The circadian phase shift was calculated with a3 parameter logistic formula3:

, where y=phase shift in hours, a=0.240, b=120, c=-3.00, x=lux.

 

However, because this study only compared the phase shift after a 6.5 hour duration, the whole right side is then divided by 6.5 and multiplied by the exposure duration provided in the spreadsheet. Because no tests were done with different wavelengths of light, only the total lux is accounted for and an uniform phase shift is assumed regardless of the specific light wavelengths.

For light emitters, total black body emitters are presumed. Planck’s law is then used to calculate the proportions of specific intervals of light that are emitted from certain kelvin temperatures of the light source as a proportion of all visible light.

Certain light filters are then applied to these numbers to reduce them by a certain percentage, shown in the picture below. Homogenous, constant melatonin suppression is assumed for the different wavelengths.

(https://glarminy.com/blue-light-blocking-glasses/, accessed 12 Mar 2020).

At this point in time, there are two studies that describe the relation of SWS reduction to light intensity1,4. However, because both studies only compared single light intensity-situations, no conclusions about a relationship between the suppression and light intensity could be drawn here. In the future, the community is going to test this out to draw more specific correlations.

Main author: Crimson
Special thanks to: evg-zhabotinsky and boostmaster
Page last updated: 27 March 2020

1.
Cho, J.R., Joo, E.Y., Koo, D.L. and Hong, S.B. Let there be no light: the effect of bedside light on sleep quality and background electroencephalographic rhythms. Sleep medicine, 2013;14(12);1422-1425. doi:10.1016/j.sleep.2013.09.007
2.
Brainard, G.C., Hanifin, J.P., Greeson, J.M., Byrne, B., Glickman, G., Gerner, E. and Rollag, M.D. Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor. Journal of Neuroscience, 2001;21(16);6405-6412. doi:10.1523/JNEUROSCI.21-16-06405.2001
3.
Zeitzer, J.M., Dijk, D.J., Kronauer, R.E., Brown, E.N. and Czeisler, C.A. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. The Journal of physiology, 2000;526(3);695-702. doi:10.1111/j.1469-7793.2000.00695.x
4.
Munch, M., Kobialka, S., Steiner, R., Oelhafen, P., Wirz-Justice, A. and Cajochen, C. Wavelength-dependent effects of evening light exposure on sleep architecture and sleep EEG power density in men. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2006;290(5);R1421-R1428. doi:10.1152/ajpregu.00478.2005