Bike Light Database

Pros:

• Very cheap; high light-to-dollar ratio.
• Can be fitted with a spot lens (default) or a diffused flood lens (sold separately).
• Rechargeable, although using a separate non-standard adapter, unlike many lights which use USB for charging.
• Adjustable brightness.

Cons:

• Bulky external battery pack.
• Battery pack does not appear to be entirely water proofed – only “water resistant”.
• Not sold directly by a reputable manufacturer – warranty support is unlikely to be available.
• Difficult to remove from the bike, especially due to the position of the plug. The plug is a good 15 inches or so away from the light, so if you wrap the cable around your handlebars or top tube at all, it's not very quick-release friendly.
• Actual output is only half of the claimed 1200 lumens, measured at 610 lumens.
• The beam shape is not very useful - with the standard lens you get an absurdly bright hot spot but little spill. The wide-angle lens is a bit better, but you still end up with a narrow (but wide) band of bright light. The optics are not thought out, they're just thrown together with the simplest parts possible.

This light (and many others like it) are massively popular because you get a lot of light for a low price. And at about $25, it’s hard to argue against the economics. However, the light only actually puts out 600 lumens. The concentrating optics make the light seem bright because all of the light is focused in one place.

Edit, November 2014: I've been getting a lot of inquiries about lights like these lately. The general sentiment from my 2013 review is the same, but here are some more detailed thoughts about this type of generic light.

The main problem with generic lights like this is the wide variation in the quality and performance. It's almost a given that the specs will be overstated, but hard to tell by how much. There are few quality controls, and many different individual manufacturers sell identical-looking lights under the same Amazon listings and with the same eBay product names.

The biggest area of variation is in the batteries. I've purchased a handful of these generic lights to compare, and the batteries have ranged from 4 hours to 15 minutes of output on the highest setting. Sometimes the batteries will keep working for many cycles, other times they die within a month or two of use. It's possible to order replacement batteries online, but you're taking the same gamble, and this adds to the cost over time. I haven't personally heard of anybody experiencing fires or explosions with these batteries, but it's a possibility when dealing with low-quality lithium batteries.

Lumen claims are of course completely bogus on these types of lights. The actual output may be anywhere from 600 - 800 lumens for a light advertised as 1200. More recently, lights have started to pop up claiming anywhere from 5000 to 10000 lumens. Even if those numbers were true, 5k (let alone 10k) lumens is far more than you would ever need and more than enough to blind someone. People like big numbers, but bigger isn't always better. Remember, the average car's headlights put out around 3000 lumens, and the optics spread that light over a much wider area than these bike lights do. Some types of riding may need those levels of output, but most don't.

That brings us to the next big issue: optics. These cheap lights have little thought put into the optics. They tend to dump a very bright spot of light will very little light spilling to the sides. This essentially washes out your vision by over-illuminating the area directly in front of you, making it difficult to see anything to either side. A good bike light focuses the beam evenly and smoothly so that you get a bit more light to the front to penetrate into the distance, but can still see the full width of the road and terrain nearby.

There are diffusing lenses available separately, which improve the situation slightly, but still don't compare to a real bike light. These diffusing lenses create a wide (horizontally) beam of light that is too short (vertically) to evenly illuminate near and far. Compare the beamshots of the Generic T6 light with a cheap diffuser lens to the L&M Taz 1000 with its custom optics. The generic light has a bright strip of light arond 50 feet, but not much light in the foreground. The Taz has a very even amount of light that gradually and smoothly fades out at a long distance. The comparison also gives a good visualization of the difference between "1200 lumens" and 1000 real, tested lumens.

Finally, there are all the features, large and small, that contribute to the convenience and ease of use of a light. The mounts are typically just a simple rubber band. The batteries are external, and the quick-disconnect is located far from the lighthead. This makes it difficult to quickly remove the light and bring it with if you lock your bike up in a theft-prone area. The battery packs are not usually waterproof, and the flimsy velcro case they come in often falls apart after a brief period of use.

These lights are designed to be built as quickly and cheaply as possible. If you need a lot of light and are on a really tight budget, they absolutely give you a lot of light per dollar. However, you get what you pay for. These lights are good at delivering a lot of output, but that's about all they do. It's an LED and a battery wired together with as little in between as possible.

Note: These lights are sold by various different vendors under a variety of names. Most of the lights are identical, but the quality of the battery pack and the included accessories may vary. The price and link displayed above are for the lowest-priced option of those we monitor the prices for, but you may want to search Amazon for "Cree T6 Bike Light" to see other options.