Led lighting. a complex subject where the leds range from really good to absolute crap with seemingly little rhyme or reason. I hope to try and answer some of these questions
First off, you might see leds called '5050' or '5630' or '2835' but what do those model numbers mean? Well they are SMD codes for the size of the led in 0.1mm. so a 5630 is 5.6mm x 3.0mm and a 5050 is 5mm x 5mm.
5050 is going to be generally the biggest LED you find commonly and is a nice square led so tends to fill light strips nicely. Bigger numbers are not always better, as for example the 5630 has less surface area then the 5050 since its rectangular, you have to compare the first two digits and last two separately.
Bigger does not always mean brighter however. Large leds can be made with very low current ratings, so high quality small leds will beat very cheap large leds. The best indicator of led performance is the rated current as most sellers lie about the rated wattage.
About LED Strips
When dealing with light strips, they generally will tell you an 'led/meter' figure that tells you how many leds you'll find per meter. The most common sizes are 30, 60, 120, 144 led/m. 100, 180, 204, 280 and 300 led/m also exist but are rare The highest density you will find for 5050 leds is generally going to be 120 or 144led/m. I believe 120/144 is the highest fill (leds to dark area ratio) you'll find for leds as higher led/m just use much smaller leds. Individually addressable LED strips require a controller to turn on or do anything. You can tell if its individually addressable because they will call it such and often describe it using a control IC like WS2812B. You must match your controller with the control IC. Individually addressable LED strips come in 30, 60 and 144 led/m, while dumb led strips that just require power be applied come in 30, 60, 120, 180, 204, 280 and 300 led/m. Basic and intelligent LED strips often come in 1M/2M/3M/4M/5M lengths, but only the 1M lengths seem to be commonly sold in 120/144 led density, likely due to the high current draw required.
They also make dumb 'RBG' strips where every led of the same color is connected to its own power wire, I believe these you could configure to any color by using a PWM controller or just large resistors in series with individual color inputs. I have noticed these in 30, 60 and 120 led/m, with some 'dual row' RGB+white strips being 120led/m but since its two rows its only as dense as 60led/m.
Led strips are commonly available in bare (PCB only), silicone coated or silicone tube waterproof. They are generally not sealed very well and would need additional sealant on the ends of the tube to become truly water proof.
Next we have COB leds. Or 'chip on board' where the led dies are welded/soldered directly to the PCB and then some goop is put on top of the LED. While these often look like a continuous light panel they are still individual leds, and nobody seems to offer any indication of LED density. Some do still show individual led dots, often due to resistors and other circuity under the goop blocking light. COB are available in all kinds of square/rectangular sizes. up to about 20cm long. They are generally a single fixed color and I have not seen any RGB cob lights or intelligent ones. Note that not all cob leds are designed to run without a heat sink but many are. They seem more suited to stuffing into incandescent fixtures like turn signals. Most are bare boards with solder terminals or wires, but a small number of COB boards prepackaged into a water proof case do exist, most commonly very cheap 14 and 17cm white led strips
Led brightness is a difficult issue. It will be affected by many things such as the viewing angle as if the viewing angle is 2x as wide, the light will be 1/4 as bright because it has to cover 4x as much area with the same amount of light.
Also the wattage of most leds is often extremely exaggerated and is best ignored. What you should do is find out the current draw and multiply it by the rated voltage. so a 0.5A led * 12v = 6W led. You can expect an led watt to be about 7 times as bright as an incandescent bulb, so a 6W led becomes the equivalent of a 42W incandescent bulb. As for efficiency of an led, In general most multiple led products are designed to run multiple leds in series to make it more efficient at 12v, getting about 70% of the power to the leds, or may even have some kind of SMPS that makes running the leds 80 to 90% efficient. But it is possible for them to just run one led in series and you would only get 30% efficiency. This would be rather rare however, so its generally safe to assume that most of the power given to an LED will actually be used to produce light, but that higher quality led products may be 20%+ more efficient then cheap led products, before even taking into account the lens and optics.
Powering lights from E-bikes
As for how to power you lights from your e-bike, while you will find a small range of lighting products designed for 36/48/52/60 and sometimes even 72v batteries, we have had much better success buying a 36~72v to 12v converter off ebay/amazon and just buying 12v automotive/motorcycle lighting and controls as there is a much better section in 12v then 36v+. Most decent lighting designed for e-bike voltages is also rather expensive. You can also get 12v blinkers and brake light flashers very cheaply on ebay.
How many watts do I need?
Incandescent car turn signals are around 27W for turning and another 8W for running light. this translates to about 3.8W for each LED turn signal and 1.1W for each LED running light. While you don't need to be as bright as a car I would highly suggest it is something to aim for and even consider exceeding. Car headlights are typically 50W each or about 7W in LED equivalent watts. LED strip lights come in wattages from 5 to 43W per meter. While led strips make poor headlights, they can be used for rather nice turn signals and running lights. Consider for on road headlights that the optics are of extreme importance to put the light where you need it and not into the eyes of other drivers. Many e-bikers have bought high power LED flood/spot lights expecting them to be good headlights only to find out they don't let you see very well and tend to blind all on coming traffic. Consider DOT or similar rated motorcycle headlights just because they tend to have optics that put the light in the correct direction.