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Thread: Why you should use red light for watching nocturnal animals

  1. #1
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    Default Why you should use red light for watching nocturnal animals

    In 1997 I visited Barna Mia animal sanctuary in the Dryandra woodland WA. My guide supplied me a 50 watt halogen spotlight fitted with a deep red filter to watch at close range a bunch of rare native mammals including Western barred-bandicoots, Woylies, and Bilbies. To my dismay the animals behaved as if they were oblivious to the red light and their pupils remained fully dilated even when my spotlight was only a couple of metres away. More recently I found the same was true when watching Kiwis on Stewart Island in NZ. Some game parks in Africa also use red light exclusively for spotlighting at night.

    My curiosity got the better of me as I had recently paid big money for an infrared viewer to watch owls nesting, only to discover you can view them more clearly without disturbance by using a cheap deep-red light and a pair of binocs. After a fair amount of Googling I discovered why.

    There are two fundamental types of light receptors in the retina of the eye called Cones and Rods. Cones are active in bright light only and because we have three different types of cones, each sensitive to different spectral wavelengths, our brain can combine the signals to enable us to see colours.

    Rods are far more sensitive to light than cones and they allow animals to see at night. Most animals including humans, have only one type of rod which has a peak spectral sensitivity near 505nm (cyan colour) and has virtually no sensitivity to light wavelengths greater than 650nm (deep red). The most important consequence of this for viewing nocturnal animals is that red light does not harm their night vision and they continue to function normally when illuminated with red light.

    Humans have three types of cone cells which have peak sensitivities to blue light(S-cones), green light (M-cones) and red light (L-cones). It is our red sensitive L-cones that enable us to see red when we use red light at night. The retinas of most nocturnal animals however, do not have L-cones which means they are oblivious when we illuminate them using red light.

    I have used red light when spotlighting for several years now and the main disadvantages are that I cannot distinguish colour and cannot identify different species by the colour of their eyeshine. When that happens I turn on the white light.
    Richard Jackson
    http://www.owlphotographer.com/
    your comments and suggestions are welcomed

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    Alan Nicol (11-05-2012), Dan Weller (09-08-2012), Mark Young (12-05-2012)

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    Very interesting Richard.
    I wonder if something as simple as red cellophane over a torch would have the same affect... and if achieving camera focus (auto or manual) would be possible?

    If it would I could see benefit for those spending time hoping for the perfect pose from an owl while reducing the disturbance to the animal.


    Cheers

    Cameron
    Cheers

    Cameron

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    A very interesting read Richard and thanks for sharing.
    View my latest review of the Canon EF400 5.6L View my trip report to Auckland Islands, NZ
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    Thanks for that Richard. I was very much aware that red light is the best (and recommended especially) for nocturnal viewing of animals as it did not affect their night vision; but it's been a while since I learnt the science behind and had forgotten!

    To Cameron - yes, I know quite a few people overseas use the red cellophane trick - never used it myself, but apparently has good results
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    Cameron and Dale,

    You are correct in that red cellophane over your light is far less intrusive than white light.

    If you look at the graph for rod sensitivity below, you will notice that rods are most sensitive to light around 500nm wavelength (cyan). Consequently cyan is the best colour light to spoil night vision! You will also notice that Rod sensitivity decreases with wavelengths above 500nm and at 650nm (deep red) rods are totally insensitive. From this it follows that for watching nocturnal animals yellow light is better than white, orange better than yellow, red better than orange and deep red (650nm) the best.
    Attachment 18299
    Thanks for your comments
    Richard Jackson
    http://www.owlphotographer.com/
    your comments and suggestions are welcomed

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    Dale Mengel (12-05-2012)

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    Thanks Richard. I remember reading an article in Nature magazine about 10 years ago on this very topic warning about the use of white lights on nocturnal animals. I'm a bit sceptical of people who say there is no difference if you use white or red light as they see no change in the subjects behaviour. I know when I've got my telescope out looking at the heavens, and if I use white light to check out star charts either in a book or my laptop, if I don't use red cellophane over the light, or use the red light in the software app, it takes a heck of a lot longer for my eyes to re-adjust to the dark light. I can only imagine how hard it is for nocturnal animals.

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    Well done Richard, I took my new LED headlamp out the other night and felt it was doing no good to the animals I shone it near. So is cellophane the answer or is there something better? As an aside, aircrew illuminate with dull red light when night flying to preserve vision.
    Kind regards Trevor.

    Website: www.trevormurrayphotography.com

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    Hi Trevor,

    The main drawback I see with using filters is that they reduce your light output. You could try using a red photographic filter over the front of your LED headlamp and that would probably be much better than cellophane.

    I have built several very bright Red LED headlamps using 3watt 630nm LEDS and these are excellent. I have not yet found a commercial red headlamp with decent light output although Energizer make several with a weak red LED, for astronomical purposes I think.

    Halogen spotlights or shooters spotlights which have red filters are excellent but they are large, expensive and heavy because they need a big powerful battery.

    If you want to build a very simple bright RED LED light I can send you the circuit diagram and tell you where to buy the bits you need. The cost of the electronics, 3W red LED and focussing optics would be of the order of $50. I cant help you with the hardware or building it.

    My one below has a 3watt Red Led with focussing lens and a 3 Watt white led and is powered by a rechargeable 3.6V lithium cell.

    Cheers
    Attachment 18315
    Richard Jackson
    http://www.owlphotographer.com/
    your comments and suggestions are welcomed

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    Thanks Richard, that would be good if you could send me those details, but only do it when you have time.
    Kind regards Trevor.

    Website: www.trevormurrayphotography.com

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    Quote Originally Posted by TrevorM View Post
    Thanks Richard, that would be good if you could send me those details, but only do it when you have time.
    Trevor, these are the electronics you need as available from Jaycar. As shown it will run the LED at 350ma Current. You can do it cheaper using a tailor made resistor instead of the driver circuit but unless you tinker with electronics it's probably not worth the effort. The circuit below can also be dimmed but you need to look at the Jaycar datasheets.
    Attachment 18339
    Richard Jackson
    http://www.owlphotographer.com/
    your comments and suggestions are welcomed

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    Thanks Richard, I'll show this to my local electronic guru and get it happening.
    Kind regards Trevor.

    Website: www.trevormurrayphotography.com

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    Great info thanks Richard!
    Cheers, Dave

    www.davidstowe.com.au WORKSHOPS

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    Some good scientific information here Richard.

    Having been on many night drives on African safaris I can tell you that most guides do not bother with red lights. In fact the last time I can remember a red light being used was back in the 1990's.

    What I do find disturbing is that even though some may use a red light, when we try for an image we are quite happy to aim our flash at the subject and give them a blast of white light.
    Last edited by Geoff Gates; 18-05-2012 at 08:10 AM. Reason: punctuation
    Cheers,
    Geoff


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    What I do find disturbing is that even though some may use a red light, when we try for an image we are quite happy to aim our flash at the subject and give them a blast of white light.
    Good point Geoff, as I have always wondered what damage it is doing to their eyes.
    The voices in my head may not be real, but they come up with some great ideas..

    Cheers Rev.

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