From Destinypedia, the Destiny wiki
Bright Dust is a currency used to buy applicable items from the Eververse store and the Tribute Hall. They may be occasionally rewarded from Seasonal Engrams. Bright Dust is primarily earned from weekly and additional bounties from certain vendors, such as Zavala, Lord Shaxx and the Drifter. If there is a seasonal event ongoing, and Eva Levante is present, she may offer weekly and additional bounties related to the event that rewards Bright Dust upon their completion.
Because bounties are per character, a soft cap of 1,800 (3,000 if Eva is present, whose weekly bounties provide double the normal) Bright Dust can be earned weekly, as 100 is rewarded per weekly bounty, with 6 (8 if Eva is present) weekly bounties available per character. Additional Bright Dust can be earned through the previously mentioned additional bounties. These bounties cost more than daily bounties but allow for the collection of further bright dust. The limit to said bounties is that they only offer 10 Bright Dust upon completion, however, they can be repeated continuously.
With the launch of Beyond Light and the simultaneous launch of Season of the Hunt, the base amount of Bright Dust earnable from the weekly bounties was halved to 100. Though 10,500 was added to the season pass, it has been calculated to be a net loss of earnable Bright Dust by 15,600 to 17,400, or just over 31% less Bright Dust per season. 
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