I have been growing a few varieties of chili pepper (incl. Scotch Bonnets) in my garden since April (Spring). Due to trees, other houses, etc., they only get about 6 hours of direct sunlight a day.
Is this amount of sunlight sufficient? Is there anything I can do to help them?
Light is the most important factor along with water, but peppers need higher soil temperatures for larger yields. If there is anything that you can do to make sure that the plants keep their soil temps up (like a good hardwood or rubber mulch), that should help.
I've grown jalapeños on an east-facing, sky-obstructed apartment porch before. The problem is simply that the less sun you have, the smaller yield you're going to get. In my case, I only managed about 4 tiny peppers: enough for a batch of scrambled eggs. Generally with chili plants, the more sun the better!
So depending on your varieties and how many plants you grow, you might be able to get a large enough yield to be worth it, even if they aren't as big as peppers you might buy in store.
As others have said, light is important. The only complete failures I've seen are people trying to grow them inside without enough light. 6hrs sounds great - but by default my growing area gets more (south and west facing, north Texas).
Habeneros are a type I have not tried, primarily because we wouldn't be able to find a use for the fruit. They are cultivars of a different species of pepper to most other types. Most are Capsicum Annuum cultivars. If memory serves me correctly, Habeneros are C.chinensis, so their growing requirements might be a little bit different (eg. see my other question about C.frutescens cultivars). Basically what I'm getting to, is to try and find a good seed supplier (I can recommend the one I use but I'm not sure if the forum should include such commercial references) and try some different varieties. There are pepper types that have been bred for cool weather, high heat, low heat, etc. Some of the northern ones might do well with less sun.
My Habaneros do remarkably less well than other Chili kinds in little sun, moderately cold environments. I've found Lemon Drop, Bell Pepper, and especially Rocotto types to be much more resilient. Some Rocotto types are as hot as Habaneros too.
If you plant in a garden, as opposed to pots like I do, you can try to mulch and/or bury some dead wood around your plants to keep soil temperature high, and plant wide apart so they at least don't have to fight among themselves for sun. On the other hand, I can bring my potted chilis indoors for the final harvest before winter.
