Intro: Cooling Yourself and Others
Fires and Ices may have the luxury of constant temperature control, but it is also possible, especially during the summer, for Lights to manipulate their surface temperature at will. I will briefly attempt to explain the process here, but the best thing for you to do is continually practice on your own.
We will be utilizing the unique ability of Lights to sense and manipulate wavelengths outside the visible spectrum, specifically infrared light.
Step 1: Being Aware of Infrared Light
Your powers are innate and instinctual in nature, but I've found it very helpful to be aware of the scientific facts behind their usage. Above, you'll find a diagram of the spectrum of light. The average person is only aware of the visible spectrum, though certain devices can utilize other spectrums. We Lights, on the other hand, have the ability to sense, manipulate, and even - to an extent - see light in the ultraviolet and infrared spectrums.
So how do you become aware of infrared light? Go outside, or even near a window, and put your face or arm or even your entire body in the sunlight. You will feel a certain amount of heat, depending on the season and time of day. That heat is infrared light. Many people incorrectly attribute the heat to UVA and UVB radiation (kinds of ultraviolet light not filtered by our atmosphere) but that is false. It is actually infrared light that causes this warmth. (Hence why there are infrared heaters and not UVA heaters.) So your skin, even if you were not a Light, can sense this kind of energy. The rest of you must become aware of it as well.
Practice finding the longer wavelengths that make up the infrared spectrum. It will be moving slower than the visible light you are used to manipulating (but, being light, will still be moving extremely fast!) This will take some time and effort. Do not worry about how long it takes you or how little you feel capable of manipulating the slower wave-lengths. Everything will come in time, and even the strongest Lights on record are not capable of intense feats outside of the visible spectrum.
A note: Though this will not happen for everyone, some of you will switch to viewing things in the infrared spectrum as your awareness increases. If this does occur it will look something like the image below. Do not panic, merely focus your attention back on the visible wavelengths and your eyes should adjust. If this does not occur but you are able to do what you wish with the infrared wavelengths then that is also not a cause for worry. Not every Light is capable of seeing in infrared.
Step 2: Dealing With Warmth
Once you are aware of infrared wavelengths, it will become increasingly apparent how much heat they generate when reflecting off of your skin. A great deal of infrared light from the sun can be absorbed by our skin, and this is what creates heat.
Most Lights I know and have read about automatically reject ultraviolet light and other harmful wavelengths, much in the same way Fires avoid burning and Waters avoid drowning. Infrared light, however, is not inherently harmful, and thus is takes conscious effort to keep it off of your skin.
If you find yourself over-heated, you simply manipulate the wavelengths of infrared light away from you, so that they do not touch your skin. Your body will take some time to release the heat it currently is producing, but you will not accumulate more energy (and therefore more warmth) so you will eventually reach a comfortable temperature. I say this method is simple but it does take a great deal of concentration, especially for those only recently adept at manipulating infrared radiation. Don't worry if it takes you a great deal of practice to be able to accomplish it.
Note: Be very careful to stay within the lower wavelengths and not stray into the visible spectrum. People will most likely become worried, confused, or alarmed if you start changing colors or disappear altogether! (Not that those techniques do not have their uses, but it will be distracting and inefficient if you do so.)
Of course, this method only works if you are gaining warmth from sunlight or an infrared-based heat source. Other sources of warmth will not be solved by this method. It is very useful for summer gatherings and outdoor exercise, though.
Step 3: Cooling Others
Once you are adept at directing infrared light away from yourself, you may find that you wish to help others as well. This is much more difficult, but still possible with intense effort and practice.
The method is the same, direct infrared wavelengths away from the skin of the people you wish to cool. It is, naturally, easier the closer you are to people. Being able to see them is a necessity, since it is much easier to manipulate wavelengths you can physically perceive one way or another. I have not had any luck, and I haven't heard of anyone else who has either, with doing this to someone in another room. Illusions somewhere you can't see are much easier than working with infrared or ultraviolet light somewhere you can't see! However, I have been able to cool someone I could see outdoors while I was indoors by working through a window.
Step 4: The Reverse
It is also, of course, possible to warm yourself and others by increasing the infrared energy that is directed towards them by the sun and other sources. This is simply the reverse of the method outlined above. This is exceptionally useful in winter and when it is cloudy, as the sun still emits light, albeit weaker light.
I would not advise trying either method at night, as it is very easy to become disoriented due to your vision flickering back and forth between the infrared and visible spectrums. The lower levels of light also tend to require more effort at night, and I have heard of people over-exerting themselves and blacking out.
Please always be careful to know your own personal limits in regards to your powers. Never over-exert yourself in an attempt to impress someone or learn a new technique. Everyone's limits and abilities are unique and you should never feel inadequate due to not being able to use your powers in the same fashion as someone else. All techniques presented in this article are learned from personal experience and should be utilized with necessary caution.