{"product_id":"candelor-candela-683","title":"Candelor – The Candela \/ 683 Lumens per Watt Physics Sticker","description":"\u003cp\u003eCandelor, a lantern-warden monk of The SI Guard, keeps a lantern that burns one pure green, the colour the daylight-adapted eye sees best.\u003c\/p\u003e\u003ch3\u003eThe Physics\u003c\/h3\u003e\u003cp\u003eThe candela, the SI unit of luminous intensity, links watts of light to how bright that light looks to a standard human eye. It is defined by fixing the luminous efficacy of monochromatic radiation at 540 × 10¹² Hz (a green of about 555 nm) at exactly 683 lm\/W. For other wavelengths the watts are weighted by the CIE photopic sensitivity curve V(λ).\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eΦ\u003csub\u003ev\u003c\/sub\u003e = K\u003csub\u003em\u003c\/sub\u003e ∫ V(λ) Φ\u003csub\u003ee,λ\u003c\/sub\u003e dλ,   K\u003csub\u003ecd\u003c\/sub\u003e = 683 lm\/W\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eΦ\u003csub\u003ev\u003c\/sub\u003e: luminous flux (lumen, lm)\u003c\/li\u003e\n\u003cli\u003eK\u003csub\u003ecd\u003c\/sub\u003e: luminous efficacy of 540 THz radiation, 683 lm\/W exactly (defining constant of the 2019 SI)\u003c\/li\u003e\n\u003cli\u003eK\u003csub\u003em\u003c\/sub\u003e: maximum photopic efficacy, ≈ 683 lm\/W\u003c\/li\u003e\n\u003cli\u003eV(λ): CIE photopic luminous efficiency function, peak 1 near 555 nm\u003c\/li\u003e\n\u003cli\u003eΦ\u003csub\u003ee,λ\u003c\/sub\u003e: spectral radiant flux (W\/nm)\u003c\/li\u003e\n\u003cli\u003eλ: wavelength (nm)\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eThe value 683 has been part of the candela definition since 1979; the 2019 SI rewrote the definition in terms of fixing K\u003csub\u003ecd\u003c\/sub\u003e exactly, alongside exact h, c and Δν\u003csub\u003eCs\u003c\/sub\u003e. The vacuum wavelength of 540 THz is about 555.17 nm (about 555.02 nm in standard air).\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e 683 lm\/W is not a law of nature. It is a convention chosen to keep the candela continuous with older standards, and V(λ) is a standardised average human eye. 540 THz sits very close to, but not exactly at, the peak of V(λ), so K\u003csub\u003em\u003c\/sub\u003e is very nearly, but not exactly, 683 lm\/W. Real lamps give far fewer lumens per watt, because not all their light is at the peak.\u003c\/p\u003e\u003ch3\u003eOn the sticker\u003c\/h3\u003e\u003cp\u003eCandelor holds up his lantern of acid-green flame, which lights his face and hood from below. Printed text: \u003cstrong\u003eCANDELOR\u003c\/strong\u003e with the line \u003cstrong\u003e683 lm\/W\u003c\/strong\u003e. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.\u003c\/p\u003e","brand":"Printify","offers":[{"title":"2\" × 2\" \/ White","offer_id":50963728793703,"sku":"90687721477604141739","price":4.99,"currency_code":"USD","in_stock":true},{"title":"3\" × 3\" \/ White","offer_id":50963728826471,"sku":"17095797416911264874","price":6.99,"currency_code":"USD","in_stock":true},{"title":"4\" × 4\" \/ White","offer_id":50963728859239,"sku":"43615170183866527447","price":8.99,"currency_code":"USD","in_stock":true},{"title":"6\" × 6\" \/ White","offer_id":50963728892007,"sku":"21108371953300099959","price":11.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0596\/8746\/9159\/files\/10049910233301038541_1200.jpg?v=1793664809","url":"https:\/\/pixelatedphysics.com\/hi\/products\/candelor-candela-683","provider":"Pixelated Physics","version":"1.0","type":"link"}