Are mirrors in sunny gardens a fire risk?

[Guest Gardener with Query]

Lots of people have mirrors in gardens.  I have one and would like to hang a couple more as my garden is very small.   However, I am worried about triggering a wildfire.

 

I don't understand the science - if one can use a mirror to light a fire from dry leaves etc when one is playing at survival, why don't mirrors in gardens cause problems?

 

Thanks for any advice you can offer.

[green-foam]

Hello, you have answered your own question. "if one can use a mirror to light a fire from dry leaves etc when one is playing at survival"

A normal mirror in a garden does not "play at survival" whereby you hold a magnifying glass or convex mirror at a specific angle for the sole purpose of igniting previously dried material. You need to focus the heat on a specific point to start a fire, your average mirror is flat, you need a convex (or parabolic) mirror to focus the suns rays to a small point. Even then, what you are pointing it at must already be dry and combustible. Since mirrors are mostly flat, that is why you do not hear of fires in gardens caused by mirrors.

Mirrors can be quite good at making a garden look bigger than it actually is, they should be mounted at the opposite end of the garden entrance, so anyone entering the garden sees the reflection of the garden before they realise they are infact looking in a mirror. It has been done for centuries with no problems.

[Guest Guest Gardener with Query]

Thank you very much for your very clear explanation of the science. I wondered whether mirrors for deliberately starting fires had to be concave, so I'm glad to hear that this is the case. I'm glad to be able to go ahead with my plans.

It was also kind of you to give additional advice about where to position the mirrors.  Unfortunately, this does not work for my very small very rectangular garden, as the last thing I would want would be to see myself and the back of my house reflected whenever I look out of the window or go into the garden.  But they work very well in gaps on the side fences, so that I am looking diagonally further down the garden when I sit at the top of the garden. But your advice on this may be useful to others.

Thanks again for your help.