There are many questions you can ask on CPF but which torch/flashlight is probably not the best one as now you'll be inundated with suggestions!....LOL!
Although not an LEO (I'm a UK paramedic) some of the concerns about firearms that our American cousins have to deal with are substantially different over here. Also it is very unlikely you'll have much to do with firearms in your first two years as a probationer. However, the need to have access to a light depends on what you are doing and for how long. For normal stop & search too powerful a light is neither necessary or desirable. For a prolonged search in a rural or semi-rural area many of the smaller LED lights cant compete with a powerful hand lamp. However, it is likely that your force 'may' provide hand lamps for that purpose anyway. IMHO a reasonably powerful LED light is ideal as it stretches out burn time on a set of primary or rechargeable cells. With the cost of lithium batteries this is not an issue to be taken too lightly. Some of the most important things to think about are reliability, carry ability, access and size. In addition to the above is does the light come with a warranty?
From a personal perspective I would never be without a primary light on my belt and a good but smaller backup for those moments when the light fails or batteries die. Trust me it happens! After years of trying different things I concluded that I needed something that would light up an address at the end of large UK garden or several car lengths away. Throw for my purposes is not as important as spill, unless you are going to be working in the boonies? Battery burn time and reliability mean more to me than anything else and reliability isn't easily come by. Lastly, accessibility and how you carry a light are equally as important issue to consider. If you can't access your light quickly when required you may as well not carry it. If it is not secure when carried it'll get dropped or lost.
My solution was to buy a Surefire G2z and equip it with a Malkoff M60L drop in carried in a Surefire V70 holster. For backup I've got a Surefire E1B Backup. I chose Surefire because they make some of the best and most reliable lights out there and their warranty is second to none. In addition the G2/G3 series of lights are reasonably cheap and pretty near indestructable. Being Nitrolon they don't show cosmetic damage easily once dropped and are comfy to hold in ungloved hands at any time of year. Nitrolon means that G2's/G2z's can be bought for £30-£40 pounds and in a pinch can be held between your teeth without problems. *Don't try that with a aluminum Surefire as the knurling with chip your teeth!*
The Malkoff dropin will provide at least 140 lumens which is ample to illuminate something at approximately 150ft away. In addition it will last for 4-4.5 hours on one set of primary cells or 1-1.5 hours on rechargeables. The V70 holster is without one of the best ways I've ever carried a torch/flashlight. It allows easy and instant access and no fumbling to reholster. It is also in the case of the G2z very, very, secure. In fact I've never had to worry about loosing my light during any activities I've done over the past few years and that includes running,climbing and being perched in some very unusual postions!!
The choice of backup was made because the E1b provides nearly as good a light as the G2z/Malkoff combo except it is a lot smaller and only uses one cell. Whilst this light isn't to be thought of as a primary light you will be able to keep it on your person on or off duty for those times when you really need a light with nearly all the attributes of your main carry.
Of course others will tell you different things and you will have to make your own mind up. Surefire is my personal favourite but there are loads of other brands which have equally as good a reputation if perhaps not so easily found in the UK.
Anyway let us know what you go with and good luck with your new career!
Doug