Those 8x30's of Warren's are great binoculars. I would use them for general hunting conditions. When comparing one bino to another, Physics helps. Logic would tell you that a larger ocular lens, i.e. higher mm number for the forward lens system (be it a single riflescope lens or dual binocular lenses) will transmit more light. That is partially true. "Transmit", by the way. is the proper term. It is absolutely impossible for a lens system to "gather" light! Optics reflect existing light.
The human eye cannot absorb (or is not capable of) processing more light (optical factor) than 7cm of "exit" (pupil) light. To compute the exit light factor you divide the objective lens by the power rating of your optics. This formula has been used for decades and is the main reason for certain (old school, if you will) optic acceptance. Examples: Ever heard of a fixed power scope? Sure you have. They are still the most superb for clarity, although not as well accepted as a few years ago. The standards were 6X42mm and 8x56mm. Fine European scopes, such as Kahles, Swarovski, Schmidt & Bender and Zeiss used these power ranges (and still do) for decades! Divide the mm (Lens diameter) by the power of the scope...Wallah: 7cms !!
8x56mm binoculars transmit the most light. 7x42 a little less. 8x30mm even less, especially at very low light when transmission is more difficult to achieve. The 10 power Pentax binos I use as a general bino are 10x42mm. The maximum amount of light that can pass through to your eye is 4.2cm..."BUT"...it's just fine for general conditions, just as Warren's will be.
OK: I'll shut up. It's just a simple barometer to compare one to another...that's all.
Best, Capt. Chris