Lighting is a key element of composition at all times, but in the travel, street, and the architectural photography I do while traveling it is a real challenge.  So much so that if one is not prepared to quickly deal with lighting problems as they present themselves images can be utterly ruined.  Many of the images being posted in my Spain series present real difficulty in execution, but by utilizing certain techniques the situation was manageable.  Here is a brief summary of strategies I use.

1.  I always shoot in RAW format.  Why is this important?  Because it is only in this format that the maximum potential of your camera can be realized.  When one shoots JPEGs the images are compressed in your camera with a resulting loss of something on the order of 70% of the information contained in the pixels.  My camera, for instance yields a 12.3mp image.  If I shoot JPEGs I wind up with roughly 3.5mp, a huge reduction in image size.  This has a direct influence on the quality of the image and what can be done with it in post production and output.  If you are not shooting RAW you are "going to bat" with two strikes against you at the outset.

2.  Do as much pre-trip research as possible before leaving home.  With copious information available on the internet these days there is no excuse for going on a photo trip unprepared about the subject matter that will be encountered.  This takes a bit of time and effort but I at least know what type of photos I will be taking, equipment  I will need, and some idea of how I will approach it.  

3.  Try to shoot at optimum times, e.g., early morning and evening.  I am often ridiculed when I talk of civil twilight.  Then the laughter increases when I explain what that means.  That means I'm "out there" (pun intended) and ready to shoot roughly a half hour before sunrise and a half hour after sunset.  That being said, when one is part of a tour that is not going to happen.  More likely one is going to be photographing at the worst possible times, challenged for time, surrounded by crowds, and more than likely under equipped.  On only one occasion on my recent Spain trip was I able to sneak out early in the morning to catch a sunrise.  So one must do the best he can to find compositions, or position one's self where the lighting is at least decent.  This is a real challenge perhaps best met by doing good subject research so one knows what angles might be available or having some idea of what can be done in post production (more about this later).  In any case the trick is to try to find the best composition while not losing your group.  Understand you're probably not going to get the "iconic" shot the National Geographic photographer is going to get.

4.  Don't be afraid to dial up the ISO.  I generally try to shoot with an ISO as low as possible, say 100-200.  The ISO is the sensitivity of your camera sensor; for those still shooting film, the film speed.  Low sensitivity generally translates to low "noise "in your images.  It is also a factor when images are "blown up" to large sizes.  The more noise the more it becomes evident as image size increases.  This becomes an issue in low light conditions, like inside churches and other buildings.  Ideally one should use a tripod to hold the camera steady in long exposure situations.  Unfortunately that is not practical in most situations.  Tripods are often not allowed, and  even if they were not practical because of time involved to set one up and crowds to trip over them.  In such situations one should not hesitate to '"crank up" the ISO.  I would rather do that than risk, or indeed, assure myself of blurred images.  Modern sensors are capable of high ISOs without producing excessive noise.  I have routinely gone up to 800 ISO and even 1600 ISO with acceptable results.  That gives me 3, maybe 4 stops of extra speed, huge in difficult conditions.  It's the difference in getting the shot and getting nothing.  Many people try to overcome low light with built-in flash. Unless your subject is very close to the camera that will be ineffective as built in flash just isn't poweful enough to reach very far.  I'm often reminded of people trying to shoot photos in a darkened stadium with a point and shoot and built-in flash.  They think they are illuminating the scene but all they're really lighting is the back of the head of the guy in front of them.  Additionally I find flash in a darkened interior very unsatisfactory lighting.  It's harsh and uneven.  

5.  Another technique which I find few know about is HDR (even though it's been around awhile), High Dyamic Range photography.  In order to utilize this one needs to have a camera that can be set to produce bursts of at least three images at a high rate of speed.  It is best to do this using a tripod, but again we are assuming such is not available.  The idea is to produce at least three identical images at the same f-stop but using three different shutter speeds 1-stop apart.  To do this in low light the ISO must be set so that the camera can be hand held steadily throughout the three bursts.  I find three bursts sufficient to produce an acceptable image; I doubt if I could hold the camera steady for more.  The resulting images are then combined in HDR software in post production to produce one image.  The idea here is to increase the range of light captured which is then translated into the final image.  It does tend to "flatten" out the lighting but with practice the final image can be quite acceptable.  I not only use this technique in low light but in situations where the contrast, or range of light present in the scene, is beyond that which the camera can capture without blowing out highlights or blocking up shadows, roughly say five f-stops of range.  I don't actually measure the dynamic range because I'm generally on the move, but with experience one will know instantly when HDR is appropriate.  This is generally not a good technique when there are moving people in the scene unless blurring their movement is not a big issue.  I find it a very efficacious technique and use it often.

6.  If your camera has a built-in flash it can be useful as a fill flash technique or where the subject is close to the camera; otherwise forget it.

7.  I always photograph with an eye to post production, what I intend to do with the image once it's uploaded to my computer.  I have a very specific workflow procedure that employs a number of software programs.  Everything starts in my basic program, LIGHTROOM.  I do primary RAW editing there and depending on the type image (for instance, most all architectural images) correct for lens  aberration.  I then move into Photoshop through which I access various special effect filters in plug-in software to finish the image to my taste.  These might include contrast, graduated, polarizing, softening , etc., filters depending on the "look" I am trying to achieve.  Some of the filters I formerly used on camera, e.g., graduated neutral density filters, I now wait until post production (at least for travel photos) because I haven't the time to mess with them or room to pack them around.  This may rub purists who think everything has to be done in camera the wrong way, but my results are the same with less hassle in the field. The point is in travel and street photography to get the job done without a lot of gear and quickly.  One just doesn't have time to stand around and analyze a scene then reach into a deep bag of gear for the proper tool. With this type of photography less is usually more.

8.  One last note with regard to gear, my bag usually consists of one camera body, a single lens (Nikkor 18-300 zoom), a polarizing  filter, perhaps a fisheye lens if I have something specific in mind for it, an extra battery for the camera,  and usually a light weight travel tripod with a ball head.  I also often carry a Lensbaby lens and a couple optics in case I want to do something a bit more artistic.  I have been using a Lensbaby system for two or three years and find it gives me an extra dimension although there is a learning curve to use it effectively.  That's it.

So, those used to lugging around a lot of gear will see this as a pretty sparse setup, but after a lot of trial and error I find this effective in these days of strict baggage limitations where I for one do not want my camera gear out of my sight, and where time and efficiency is critical.  Even more importantly, these lighting tips will solve most challenging situations you're liable to encounter.