I don't know enough about silent illumination to comment.
Two more distinctions are probably useful for you to understand.
Some make distinctions between Momentary vs access and types of jhana.
U Pandita:There are two types of jhāna: samatha jhāna and vipassanā jhāna. Some of you may have read about the samatha jhānas and wonder why I am talking about them in the context of vipassanā. Samatha jhāna is pure concentration, fixed awareness of a single object — a mental image, for example, such as a colored disk or a light. The mind is fixed on this object without wavering or moving elsewhere.
On momentary concentration, book is Practicing the Jhanas, Pa Auk tradition:Mediators can eventually attain access concentration using either type of momentary concentration practice--samatha or vipassana. However, samatha practices are more likely to lead to access concentration because of their more stable nature. Access concentration is characterized by the significant reduction or complete dropping of the five hindrances. For most people, a period of intensive practice is required to reach access concentration. In access concentration, the meditative experience becomes smoother, easier, and more pleasant because of this lessening of hindrances and the arising of the powerful and blissful sensations of the jhana factors. This allows mediators to meditate longer and progress more easily in the practice. It becomes a positive, self-reinforcing loop.
It is easy to confuse momentary concentration with access concentration. One difference is that with access concentration the mediators continuity with the object is much longer and more stable over time. Another difference is that with access concentration, the object is much more energized and "bright"
The views on what constitutes access concentration seem to vary quite a bit, so depends on who you ask...
For example, patibhaga nimitta marks access.
Or just any level of fixed concentration free from hindrances.
Or perhaps easiest definition, Leigh B writes, "Access Concentration is a state where you are fully with the meditation object (breath) and if there are thoughts, they are wispy and in the background and do not pull you away from the breath"http://www.leighb.com/accesscon.htm
Because the term seems quite ambiguous and vague, probably best not to place too much emphasis on it. There are other things you can place emphasis on such as increase one-pointedness of mind, not being as distracted. Or if you are focusing more on piti-sukkha. Or if you are making use of nimitta. And so on.