Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014


Watts it all about

©2001 Melissa Kaplan


If it were possible to simply tell herpers to "use a 100 watt household bulb" to attain and maintain the temps the iguanas or any other herp species requires, I would state specific wattages in my articles.

The problem is that the temperatures in the room, in the house, and outside the house all affect the temperature inside an enclosure, as do the material(s) from which the enclosure is constructed. When you are talking about a free-roaming animal, the ambient room, house and outside temperatures have an even greater impact on your heating equipment.

The impact of ambient inside and outside temperatures and materials is why we also stay away from using concepts such as "room temperature." The temperature of a room will vary from room to room in a house, depending on:

  • how well insulated the house is;

  • where the outside wall of the room is facing (north, south, east, west);

  • the time of day;

  • the time of year;

  • presence of vines or trellised plants on the outside wall;

  • any trees or other buildings near enough to block full sun part or all of the day.

At the time of this writing, it is 7:49 AM in Sonoma County, California, on the 5th of October. The thermometer in my den reads 64 F. Come December, assuming that this coming December is going to be similar in rain, winds, etc., as the last couple of La Niña Decembers, the ambient room air temperature at noon in this same den will, if I'm lucky, be around 53 F. At this same time of the morning in July-August, the temp is generally 68-70, depending on how much of a marine layer we had during the night and that morning.

Now, if I use a 100 watt bulb during the summer, when the ambient room air temperature can rise to 90+ F in the afternoons in my den, the enclosure may get too hot for the lizard. I have a couple of options, depending on which, through trial and error, I find works for that particular enclosure in that particular place in that particular room: I can use a lamp dimmer device to decrease the bulb's output during the days when the ambient room air temp is such that it gets too hot in there, or I can switch to a lower wattage bulb (the actual wattage to be determined through trying out a couple of different bulbs, such as a 60 watt and a 40 watt) during the summer, reinstalling the 100 watt bulb during the winter.

For winter, I may need two 100 watt bulbs, or a 100 watt and a 100-250 watt CHE, again, depending on what I find that works to enable me to make sure that that enclosure maintains the tropical temperatures required by the lizard. An enclosure made from different materials, or of a different size, may require more - or less - heat. Moving that enclosure from one side of the room to another, say from next to an inside wall to next to an outside wall, can also affect the ability of that 100 watt bulb to attain and maintain the necessary temperatures.

Fall Into Heating Problems
Fall is the time of year when reptile forums and my email starts to blossom with messages reading "my reptile isn't eating like it used to" and "my reptile is blowing bubbles out its nose and wheezing when it breathes". The vast majority of these reports are from owners who haven't figured out that, as the temperatures outside their homes gets cooler during the day and the night mean the building - and individual rooms - and enclosures in those rooms - within their homes are losing more heat during the night, making them all colder in the morning. This in turn means that the heating equipment and settings they were using during the summer are no longer able to attain or maintain the temperatures they did during the summer. That's why I wrote my Winter Advisory article several years ago, which actually grew out of my answering the same types of questions every Fall.

So, while a 100 - or 60 or 250 - watt bulb may work great for someone else, that doesn't mean it will work that way for you. That is why the articles I and others write - and the responses of so many posts - stress is on the need to use thermometers and monitor the actual temperatures, adding or subtracting watts or heat sources as required to attain and maintain the temps each species needs, rather than simply stating specific watts.

Related Articles

Lighting & Heating

Winter Advisory

Microclimates: Dealing with Summer Heat and Low Ambient Humidity

Emergency Preparedness

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