What may seem like a simple question is actually the most difficult of all the questions we are asked each and every day. Start with the bulb type: base socket (dozens of variations), input voltage (ranges from 120VAC to 480VAC - US), wattage (8w to over 1,000w), manufacturer and glass (clear or diffused). There are literally over ten thousand different fixtures from hundreds of manufacturers globally so finding a spec sheet on many fixtures can be the proverbial needle in a haystack search. Add to this the technology changes for traditional ballasts, bulb types and fixture modifications and this multiplies the search. Finally, for fluorescent there are several ballast types and varying connection protocols--a simple remove and replace is not as simple as your local retail box store or electrical distributor will explain. The easiest remove and replace is likely incandescent; but then LED quality plays a substantial part in choosing even the simplest of replacements.