How To Test How Much Sun Your Garden Gets

Someone on a social site asked if anyone knew of a light meter that would measure the amount of light in their garden. I burst out in laughter thinking this was a great joke. Then someone posted a link to just such a product; the Sunlight Calculator. I cried. Are people really buying such a product?

Sunlight Calculator, a product you don't need

Sunlight Calculator – The Claims

The following are taken from the dealers ad.

"The lighting conditions of the micro-climates in your garden aren't always obvious." Yes they are – just hold out your hand and look for shadows.
"This meter measures the duration and intensity of sunlight falling at a given spot over a 12-hour period." It might measure these things but it does not report them. It only reports sun, part sun, part shade or shade. You get neither duration nor intensity readings.
"Though not a panacea for all garden problems, it can help you locate plants where they will grow best." Not really, since light levels are just one of the parameters to consider.

SunCalc® – How It Works

After you turn it on, the meter measure the amount of light for 12 hours and determines how much sun you have. That is simple enough.

What happens if you turn it on at noon?

Sunlight Calculator then measure light for only part of the day, and will give you the wrong readings. So to make this work you need to go outside and turn it on before sunup. Sorry – I am in bed sleeping.

Results

The Sunlight Calculator gives one of four readings which translate into the following.

Full sun: 6+ hours
Partial sun: 4-6 hours
Partial shade: 1.5 – 4 hours
Full shade: less then 1.5 hours

May I suggest that if you go outside 3 or 4 times during a single day, and look up, you can determine these values without a meter. Warning – do not look directly at the sun.

If you are a visual learner, my video will show you how to make a sun map.

If the above video does not play, use this link: https://youtu.be/AAIhO_olcDg

Isolation Level

Two-thirds of the technical brochure deals with something called "isolation level". There are lots of formulas and technical information on this, but it never tells you how you should use the information.

Here is some of it. WARNING: read this only if you want a nap .

The values are generally expressed in kWh/m²/day. This is the amount of solar energy that strikes a square meter of the earth's surface in a single day. Of course, this value is averaged to account for differences in day length. There are several units used throughout the world.

Garden Myths book by Robert Pavlis

The conversions based on surface area are: 1 kWh/m²/day = 317.1 btu/ft²/day = 3.6MJ/m²/day

The raw energy conversions are:1kWh = 3412 Btu = 3.6MJ = 859.8kcal

Do they really believe gardeners are going to do these calculations?

Plants Require Sun or Shade

Some plants prefer sun and some prefer shade. Almost all will grow in part sun/shade. The more I grow things the more I am surprised that so called sun plants do just fine in shade and vice versa. The plants are adaptable.

My shade garden was shaded by two medium sized sugar maples. The two trees had to be removed one winter, and my garden was suddenly a full sun garden. All of the plants did just fine. Some of the shade plants are actually growing better now than before. Admittedly, this garden does get watered a couple of times a season, but it can go several weeks without water.

Stop Buying Unnecessary Products

The Sunlight Calculator is not something you need. You can make a sun map following the procedure in my video in less than an hour and you don't have to buy anything.

Soil Science for Gardeners book by Robert Pavlis

What really bothers me about such products is that they are damaging the environment. The product needs to be manufactured, packaged, and shipped around the country – probably half way around the world. That all takes resources including oil. In the process it adds pollution to the environment and increases global warming. You will use it once, and store it in the shed.

If you care about the environment – don't buy the Sunlight Calculator.

References

Photo source: Incremental Tools